[Freetel-codec2] Tuning Aid 700B mode

Maybe have a tune mode, where a center carrier transmits at 1500 Hz
with a di-dah-di-dah-di-dah... for 700B and di-di-di-dah-di-di-di-dah
for 700(whatever)...

------------------------------------------------------------------------------

glen english

2015-09-15 03:02:17 UTC

some sort of low level CW buried in there would be nice anyway- callsign
and mode+version.

Post by Steve
Maybe have a tune mode, where a center carrier transmits at 1500 Hz
with a di-dah-di-dah-di-dah... for 700B and di-di-di-dah-di-di-di-dah
for 700(whatever)...
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David Rowe

2015-09-15 03:06:44 UTC

Yes I'll add some "sights" to the graticule some time. An additional
complication is that the 700B carrier spacing is non-uniform, a little
trick to reduce PAPR.

- David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode and there is an absence of a distinct central carrier then a couple of extra tick marks on the FreedDV GUI showing the edges of the signal, when correctly tuned, as well as the centre would provide easier tuning of signals using coherent psk modes. Note this is compounded by having an even numbers of carriers where correct tuning is with the centre tick mark between the 7th and 8th carriers,not aligned with a carrier. It is easy to select the mid point between the wrong carrier pair.
regards
Peter VK5APR
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Bruce Perens

2015-09-15 03:30:23 UTC

How difficult would it be to widen your software PLL? That might make the
rest moot.

Post by David Rowe
Yes I'll add some "sights" to the graticule some time. An additional
complication is that the 700B carrier spacing is non-uniform, a little
trick to reduce PAPR.
- David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode

and there is an absence of a distinct central carrier then a couple of
extra tick marks on the FreedDV GUI showing the edges of the signal, when
correctly tuned, as well as the centre would provide easier tuning of
signals using coherent psk modes. Note this is compounded by having an even
numbers of carriers where correct tuning is with the centre tick mark
between the 7th and 8th carriers,not aligned with a carrier. It is easy to
select the mid point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

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Post by Peter Reichelt
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David Rowe

2015-09-15 08:42:14 UTC

The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real problem.

Post by Bruce Perens
How difficult would it be to widen your software PLL? That might make
the rest moot.
Yes I'll add some "sights" to the graticule some time. An additional
complication is that the 700B carrier spacing is non-uniform, a little
trick to reduce PAPR.
- David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the

1600 mode and there is an absence of a distinct central carrier then
a couple of extra tick marks on the FreedDV GUI showing the edges of
the signal, when correctly tuned, as well as the centre would
provide easier tuning of signals using coherent psk modes. Note this
is compounded by having an even numbers of carriers where correct
tuning is with the centre tick mark between the 7th and 8th
carriers,not aligned with a carrier. It is easy to select the mid
point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

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Stuart Longland

2015-09-21 22:39:38 UTC

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real problem.

Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.

--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.

David Rowe

2015-09-21 23:09:38 UTC

People have been tuning SSB by ear for years. I suspect we will get
used to the sound of the 700-ish waveforms (in analog mode) and be able
to get close enough by ear so the demod clicks in.

If not, no biggie to make the freq off estimation range wider.

- David

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real problem.

Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.
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Bruce Perens

2015-09-22 00:02:02 UTC

Hi David,

Having a low barrier to entry will make it more likely that users will
stick with the program long enough to learn more about it. So, if the
program could start out with a wider frequency estimation range, that would
probably be best. If there is any reason to reduce that range, the user can
do that once they have learned what the waveform should look like.

Thanks

Bruce

Post by David Rowe
People have been tuning SSB by ear for years. I suspect we will get
used to the sound of the 700-ish waveforms (in analog mode) and be able
to get close enough by ear so the demod clicks in.
If not, no biggie to make the freq off estimation range wider.
- David

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real

problem.

Post by Stuart Longland
Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.

------------------------------------------------------------------------------

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glen english

2015-09-22 00:26:09 UTC

------------------------------------------------------------------------------

David Rowe

2015-09-22 00:38:56 UTC

Just curious - have any of you actually tried 700B OTA?

how about a modulated output or something from the speaker to assist
tuning- IE a variable tone, or a series of clicks at some frequency as
to provide tuning direction feedback.
maybe fallng chirps when you are too low, and rising chirps when you are
too high... etc ?

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real problem.

--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
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Bruce Perens

2015-09-22 01:54:21 UTC

Nope. I need to make audio recordings of it because I am doing the paper on
700B at Pacificon. Nobody else could be persuaded to promote it there (or
indeed anywhere in the U.S. but Hamvention and Hamcation, where Mel and
Gerry will do it). Thursday might work. If I find that tuning is brain dead
I'll tell you then.

Post by David Rowe
Just curious - have any of you actually tried 700B OTA?

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real

problem.

Post by Stuart Longland
Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.

------------------------------------------------------------------------------

Post by Stuart Longland
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--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077

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Walter Holmes

2015-09-22 02:44:20 UTC

I guess I must really be missing something here. :)

I have been using 700 and 700B since it was first released in early beta
many weeks ago and have NEVER had an issue with tuning, as long as the
person at the other end WAS also on frequency.

As long as my radio is on the right frequency it locks on very well.

It almost sounds like we're trying to solve a problem that doesn't really
exist on the air in everyday use.

Of course with the Waterfall on a computer it will be many times easier. And
use of the QSO Finder to let people know WHAT frequency you're on, it's a no
brainer.

When you see the carriers and the bandpass filter set to 1.5k, just center
it in the waterfall screen, and done.

Since we have not had the code to try it on an SM1000 just yet, that may be
slightly more difficult, but even still, I would use the dial of the radio
to set it to either a known frequency or center up on the sound.

Just my 2 cents.. :)

Walter/K5WH

-----Original Message-----
From: David Rowe [mailto:***@rowetel.com]
Sent: Monday, September 21, 2015 7:39 PM
To: freetel-***@lists.sourceforge.net
Subject: Re: [Freetel-codec2] Tuning Aid 700B mode

Just curious - have any of you actually tried 700B OTA?

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real problem.

Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.
---------------------------------------------------------------------
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--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
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wully

2015-09-22 19:58:02 UTC

Hi all

Helmut, dc6ny, and I have done some more tests yesterday. The band
starts opening again (wonderful: we always want to test 700B).
As stated earlier, we never had any problem with the 700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the impression we get
from our experiences. Yesterday, I started to reduce my power (measured
by an LP-100A just before the antenna coupler) when txing in 700B.
Helmut detected the signal and I reported about my power seting: Full
drive started with 58Watts peak. Then I reduced the power to 100mW peak
(reading the quickly changing "average" of LP-100A). This was the last
setting, that I could read on the LP-100A, my relative powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4, to 3, to 2. After
this experiment, Helmut reported, that he could fully decode the signal
at 6, but at 5 only about 50% and lower no decoding anymore. We
estimated, that setting 6 was about 50 mWatt.

We both are very impressed by this result!

Unfortunately, during our experiment at higher power there were some
people trying to destroy our signal: I have to say, that they were
sucessful. In this respect, the 1600 was a little less critical.
But I think that this is just a remark. Against bad guys, one can not fight.

700B is realy a very good mode. I try to convince more people, to make
experiments. but it is not so easy, because amateurs today seem to sit
in their chair and enjoy not to experiment! What a difference to what we
heard from the amateurs in the twenties!

Great, to hear, that there will be presentations in conferences!

73, hb9epu

Post by Walter Holmes
I guess I must really be missing something here. :)
I have been using 700 and 700B since it was first released in early beta
many weeks ago and have NEVER had an issue with tuning, as long as the
person at the other end WAS also on frequency.
As long as my radio is on the right frequency it locks on very well.
It almost sounds like we're trying to solve a problem that doesn't really
exist on the air in everyday use.
Of course with the Waterfall on a computer it will be many times easier. And
use of the QSO Finder to let people know WHAT frequency you're on, it's a no
brainer.
When you see the carriers and the bandpass filter set to 1.5k, just center
it in the waterfall screen, and done.
Since we have not had the code to try it on an SM1000 just yet, that may be
slightly more difficult, but even still, I would use the dial of the radio
to set it to either a known frequency or center up on the sound.
Just my 2 cents.. :)
Walter/K5WH
-----Original Message-----
Sent: Monday, September 21, 2015 7:39 PM
Subject: Re: [Freetel-codec2] Tuning Aid 700B mode
Just curious - have any of you actually tried 700B OTA?

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real

problem.

Post by Stuart Longland
Tuning accuracy is likely to be an issue on headless systems or for
visually impaired operators.
---------------------------------------------------------------------
---------
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--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
----------------------------------------------------------------------
--------
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------------------------------------------------------------------------------

glen english

2015-09-22 23:26:04 UTC

Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.

something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.

73

------------------------------------------------------------------------------

Helmut

2015-09-23 08:34:59 UTC

Hi Glen,

Very difficult question, hi! I left the commercial arena more than 12 years
ago, so that have to use my old mixed surplus test equipment, certainly not
competitive with today's requirements, but good enough for ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The feedback
loop for the pre-distortion delivers an exact and well defined portion of
the TX power to the RX input in real-time. As the ADC is driven to full
scale or in minimum 15 dB below the failure is within +/- 0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling how capable
freeDV at small SNRs is, I always watch the displayed spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means that a signal is
still visible, but no longer audible after processing in the phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.

73, Helmut

p.s. No experience with AD8362. Boonton (Wireless Telecom Group) offers a
nice USB Peak Power Sensor.

-----Ursprüngliche Nachricht-----
Von: glen english [mailto:***@cortexrf.com.au]
Gesendet: Mittwoch, 23. September 2015 01:26
An: freetel-***@lists.sourceforge.net
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode

Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.

something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.

73

David Rowe

2015-09-23 20:16:02 UTC

Nice work on the power measurement Helmut :-)

I wanted to say a little about 0dB SNR and below operation. In the
attached plot, the lower three curves show the performance of modems in
AWGN channel - a channel that just has additive noise (like a very slow
fading HF channel or VHF).

These curves show how much energy/bit (Eb/No) we need for a certain Bit
Error Rate (BER).

The Blue curve just above the Red (ideal QPSK) perf is our modem in a
AWGN channel. Time for some math:

The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz) multiplied by
the bandwidth B, N=NoB

Re-arranging a bit we get:

SNR = S/N = EbRb/NoB

or in dB:

SNR(db) = Eb/No(dB) + 10log10(Rb/B)

Now Rb = 700, B = 3000 Hz (for SNR in a 3000Hz bandwidth) so we get:

SNR = Eb/No - 6.3

Now, say we need a BER of 2% or 0.02 for speech, the lower blue curve
says we need an Eb/No = 4dB, so we get:

SNR = 4 - 6.3 = -2.3dB

So if the modem is working down to "just" 0dB we are about 2dB worse
than theoretical. This is due to the extra bandwidth taken by the pilot
symbols (which translates to 1.5dB) and some implementation loss in the
sync algorithms, and non linearities in the system.

I thought it worth explaining this a little more. These skills will be
just as important to Hams of the 21st century as Ohms law was in the 20th.

Cheers,

David

Post by Helmut
Hi Glen,
Very difficult question, hi! I left the commercial arena more than 12 years
ago, so that have to use my old mixed surplus test equipment, certainly not
competitive with today's requirements, but good enough for ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The feedback
loop for the pre-distortion delivers an exact and well defined portion of
the TX power to the RX input in real-time. As the ADC is driven to full
scale or in minimum 15 dB below the failure is within +/- 0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling how capable
freeDV at small SNRs is, I always watch the displayed spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means that a signal is
still visible, but no longer audible after processing in the phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group) offers a
nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73

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Matthew Cook

2015-09-24 00:49:21 UTC

David,

Why can I see a discussion paper or magazine article entitled "do you know
your Eb/No?" *grin*.

73

Matthew
VK5ZM

Post by David Rowe
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In the
attached plot, the lower three curves show the performance of modems in
AWGN channel - a channel that just has additive noise (like a very slow
fading HF channel or VHF).
These curves show how much energy/bit (Eb/No) we need for a certain Bit
Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem in a AWGN
The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz) multiplied by
the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue curve says
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB worse than
theoretical. This is due to the extra bandwidth taken by the pilot symbols
(which translates to 1.5dB) and some implementation loss in the sync
algorithms, and non linearities in the system.
I thought it worth explaining this a little more. These skills will be
just as important to Hams of the 21st century as Ohms law was in the 20th.
Cheers,
David

Post by Helmut
Hi Glen,
Very difficult question, hi! I left the commercial arena more than 12 years
ago, so that have to use my old mixed surplus test equipment, certainly not
competitive with today's requirements, but good enough for ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The feedback
loop for the pre-distortion delivers an exact and well defined portion of
the TX power to the RX input in real-time. As the ADC is driven to full
scale or in minimum 15 dB below the failure is within +/- 0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling how capable
freeDV at small SNRs is, I always watch the displayed spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means that a signal is
still visible, but no longer audible after processing in the phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group) offers a
nice USB Peak Power Sensor.
-----UrsprÃŒngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73

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David Rowe

2015-09-24 00:56:22 UTC

Yep, I thought it worth blogging on as I keep forgetting it myself:

http://www.rowetel.com/blog/?p=4621

Have some other ideas for more later....

- David

Post by Helmut
David,
Why can I see a discussion paper or magazine article entitled "do you
know your Eb/No?" *grin*.
73
Matthew
VK5ZM
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In the
attached plot, the lower three curves show the performance of modems
in AWGN channel - a channel that just has additive noise (like a
very slow fading HF channel or VHF).
These curves show how much energy/bit (Eb/No) we need for a certain
Bit Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem in
The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz) multiplied
by the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB worse
than theoretical. This is due to the extra bandwidth taken by the
pilot symbols (which translates to 1.5dB) and some implementation
loss in the sync algorithms, and non linearities in the system.
I thought it worth explaining this a little more. These skills will
be just as important to Hams of the 21st century as Ohms law was in
the 20th.
Cheers,
David
Hi Glen,
Very difficult question, hi! I left the commercial arena more than 12 years
ago, so that have to use my old mixed surplus test equipment, certainly not
competitive with today's requirements, but good enough for ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The feedback
loop for the pre-distortion delivers an exact and well defined portion of
the TX power to the RX input in real-time. As the ADC is driven to full
scale or in minimum 15 dB below the failure is within +/- 0.3 dB
for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling how capable
freeDV at small SNRs is, I always watch the displayed spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means that a signal is
still visible, but no longer audible after processing in the phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group) offers a
nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73
Hi all
Helmut, dc6ny, and I have done some more tests yesterday. The band
starts opening again (wonderful: we always want to test 700B).
As stated earlier, we never had any problem with the
700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the
impression we get
from our experiences. Yesterday, I started to reduce my
power (measured
by an LP-100A just before the antenna coupler) when txing in 700B.
Helmut detected the signal and I reported about my power
seting: Full
drive started with 58Watts peak. Then I reduced the power to
100mW peak
(reading the quickly changing "average" of LP-100A). This
was the last
setting, that I could read on the LP-100A, my relative
powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4, to 3,
to 2. After
this experiment, Helmut reported, that he could fully decode
the signal
at 6, but at 5 only about 50% and lower no decoding anymore. We
estimated, that setting 6 was about 50 mWatt.
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Matthew Cook

2015-09-24 01:03:22 UTC

Bookmarked tnx David !

73

/M.

Post by David Rowe
http://www.rowetel.com/blog/?p=4621
Have some other ideas for more later....
- David

phones.

Post by Helmut
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group)
offers a
nice USB Peak Power Sensor.
-----UrsprÃŒngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73
Hi all
Helmut, dc6ny, and I have done some more tests yesterday.
The band
starts opening again (wonderful: we always want to test

700B).

Post by Helmut
As stated earlier, we never had any problem with the
700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the
impression we get
from our experiences. Yesterday, I started to reduce my
power (measured
by an LP-100A just before the antenna coupler) when txing in
700B.
Helmut detected the signal and I reported about my power
seting: Full
drive started with 58Watts peak. Then I reduced the power to
100mW peak
(reading the quickly changing "average" of LP-100A). This
was the last
setting, that I could read on the LP-100A, my relative
powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4, to 3,
to 2. After
this experiment, Helmut reported, that he could fully decode
the signal
at 6, but at 5 only about 50% and lower no decoding anymore.

Post by Helmut
estimated, that setting 6 was about 50 mWatt.

----------------------------------------------------------------------------

Post by Helmut
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now!

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Bruce Perens

2015-09-24 01:32:57 UTC

I was thinking, for my Pacificon talk on 700B next month, of doing a
take-off on the QST column "The World Above 50 MHz" called "The World Below
0 dB S/N".

Post by Helmut
David,
Why can I see a discussion paper or magazine article entitled "do you know
your Eb/No?" *grin*.
73
Matthew
VK5ZM

Post by David Rowe
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In the
attached plot, the lower three curves show the performance of modems in
AWGN channel - a channel that just has additive noise (like a very slow
fading HF channel or VHF).
These curves show how much energy/bit (Eb/No) we need for a certain Bit
Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem in a
The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz) multiplied by
the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue curve
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB worse than
theoretical. This is due to the extra bandwidth taken by the pilot symbols
(which translates to 1.5dB) and some implementation loss in the sync
algorithms, and non linearities in the system.
I thought it worth explaining this a little more. These skills will be
just as important to Hams of the 21st century as Ohms law was in the 20th.
Cheers,
David

Post by Helmut
Hi Glen,
Very difficult question, hi! I left the commercial arena more than 12 years
ago, so that have to use my old mixed surplus test equipment, certainly not
competitive with today's requirements, but good enough for ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The feedback
loop for the pre-distortion delivers an exact and well defined portion of
the TX power to the RX input in real-time. As the ADC is driven to full
scale or in minimum 15 dB below the failure is within +/- 0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling how capable
freeDV at small SNRs is, I always watch the displayed spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means that a signal is
still visible, but no longer audible after processing in the phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group) offers a
nice USB Peak Power Sensor.
-----UrsprÃŒngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average signals,
IE faithfully measuring peak and PEP ? I've been involved in this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73

David Rowe

2015-09-24 19:14:24 UTC

It's an challenging area to play in, I worked out the theoretical limits
for DV here:

http://www.rowetel.com/blog/?p=4053

Post by Bruce Perens
I was thinking, for my Pacificon talk on 700B next month, of doing a
take-off on the QST column "The World Above 50 MHz" called "The World
Below 0 dB S/N".
David,
Why can I see a discussion paper or magazine article entitled "do
you know your Eb/No?" *grin*.
73
Matthew
VK5ZM
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In
the attached plot, the lower three curves show the performance
of modems in AWGN channel - a channel that just has additive
noise (like a very slow fading HF channel or VHF).
These curves show how much energy/bit (Eb/No) we need for a
certain Bit Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem
The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz)
multiplied by the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB
worse than theoretical. This is due to the extra bandwidth
taken by the pilot symbols (which translates to 1.5dB) and some
implementation loss in the sync algorithms, and non linearities
in the system.
I thought it worth explaining this a little more. These skills
will be just as important to Hams of the 21st century as Ohms
law was in the 20th.
Cheers,
David
Hi Glen,
Very difficult question, hi! I left the commercial arena
more than 12 years
ago, so that have to use my old mixed surplus test
equipment, certainly not
competitive with today's requirements, but good enough for
ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a
nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar
accuracy for
sinusoidal waveforms. From time to time I check the R&S
meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup.
The feedback
loop for the pre-distortion delivers an exact and well
defined portion of
the TX power to the RX input in real-time. As the ADC is
driven to full
scale or in minimum 15 dB below the failure is within +/-
0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling
how capable
freeDV at small SNRs is, I always watch the displayed
spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means
that a signal is
still visible, but no longer audible after processing in the
phones.
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom
Group) offers a
nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to
average signals,
IE faithfully measuring peak and PEP ? I've been involved in
this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73
Hi all
Helmut, dc6ny, and I have done some more tests
yesterday. The band
starts opening again (wonderful: we always want to test
700B).
As stated earlier, we never had any problem with the
700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the
impression we get
from our experiences. Yesterday, I started to reduce my
power (measured
by an LP-100A just before the antenna coupler) when
txing in 700B.
Helmut detected the signal and I reported about my power
seting: Full
drive started with 58Watts peak. Then I reduced the
power to 100mW peak
(reading the quickly changing "average" of LP-100A).
This was the last
setting, that I could read on the LP-100A, my relative
powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4,
to 3, to 2. After
this experiment, Helmut reported, that he could fully
decode the signal
at 6, but at 5 only about 50% and lower no decoding
anymore. We
estimated, that setting 6 was about 50 mWatt.
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David Rowe

2015-09-24 20:33:01 UTC

... have just been released. I've added a "News" section to freedv.org
with brief notes on the changes.

Thanks Richard for pushing these releases out there!

- David

Post by David Rowe
It's an challenging area to play in, I worked out the theoretical limits
http://www.rowetel.com/blog/?p=4053

Post by Bruce Perens
I was thinking, for my Pacificon talk on 700B next month, of doing a
take-off on the QST column "The World Above 50 MHz" called "The World
Below 0 dB S/N".
David,
Why can I see a discussion paper or magazine article entitled "do
you know your Eb/No?" *grin*.
73
Matthew
VK5ZM
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In
the attached plot, the lower three curves show the performance
of modems in AWGN channel - a channel that just has additive
noise (like a very slow fading HF channel or VHF).
These curves show how much energy/bit (Eb/No) we need for a
certain Bit Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem
The energy/bit Eb = power/bit rate = S/Rb
The total noise the demod sees is No (noise power in 1Hz)
multiplied by the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB
worse than theoretical. This is due to the extra bandwidth
taken by the pilot symbols (which translates to 1.5dB) and some
implementation loss in the sync algorithms, and non linearities
in the system.
I thought it worth explaining this a little more. These skills
will be just as important to Hams of the 21st century as Ohms
law was in the 20th.
Cheers,
David
Hi Glen,
Very difficult question, hi! I left the commercial arena
more than 12 years
ago, so that have to use my old mixed surplus test
equipment, certainly not
competitive with today's requirements, but good enough for
ham radio.
The old R&S RMS-Powermeter with a tru-sensor provides a
nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar
accuracy for
sinusoidal waveforms. From time to time I check the R&S
meter with my (old)
HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup.
The feedback
loop for the pre-distortion delivers an exact and well
defined portion of
the TX power to the RX input in real-time. As the ADC is
driven to full
scale or in minimum 15 dB below the failure is within +/-
0.3 dB for average
or PEP indication (total dynamic range > 120 dB).
For the exciting tests with Alfred, HB9EPU, to get a feeling
how capable
freeDV at small SNRs is, I always watch the displayed
spectrum of the
incoming signal. The FFT bin width is 2,93 Hz, that means
that a signal is
still visible, but no longer audible after processing in the
phones.
Therefore it was amazing, that freeDV seems to produce
reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom
Group) offers a
nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to
average signals,
IE faithfully measuring peak and PEP ? I've been involved in
this with
DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73
Hi all
Helmut, dc6ny, and I have done some more tests
yesterday. The band
starts opening again (wonderful: we always want to test
700B).
As stated earlier, we never had any problem with the
700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the
impression we get
from our experiences. Yesterday, I started to reduce my
power (measured
by an LP-100A just before the antenna coupler) when
txing in 700B.
Helmut detected the signal and I reported about my power
seting: Full
drive started with 58Watts peak. Then I reduced the
power to 100mW peak
(reading the quickly changing "average" of LP-100A).
This was the last
setting, that I could read on the LP-100A, my relative
powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4,
to 3, to 2. After
this experiment, Helmut reported, that he could fully
decode the signal
at 6, but at 5 only about 50% and lower no decoding
anymore. We
estimated, that setting 6 was about 50 mWatt.
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Helmut

2015-09-24 06:23:25 UTC

Hi David,

many thanks for your tutorial, but I can assure you that definitions and
terms like SNR, PSNR, C/N, NPR etc. were already known and used in the 20th
century, when the majority of the communication channels were not wireless.
We only used the term SNR for our tests as it is displayed in the freeDV
window - indeed without any dimension- but as a certain benchmark to
determine the limit of readability. I learnt that this display seems to show
only tendency, but not a fix value, as freeDV doesn't know the current
bandwidth of the used channel. We e.g. can't calculate with a standard BW of
3 kHz as we reduce BW to the absolutely necessary width to keep willful
interference of some ignorant guys out of channel.

Thanks and greetings to down under.

Helmut

-----Ursprüngliche Nachricht-----
Von: David Rowe [mailto:***@rowetel.com]
Gesendet: Mittwoch, 23. September 2015 22:16
An: freetel-***@lists.sourceforge.net
Betreff: [Freetel-codec2] 0dB and below

Nice work on the power measurement Helmut :-)

I wanted to say a little about 0dB SNR and below operation. In the attached
plot, the lower three curves show the performance of modems in AWGN channel
- a channel that just has additive noise (like a very slow fading HF channel
or VHF).

These curves show how much energy/bit (Eb/No) we need for a certain Bit
Error Rate (BER).

The Blue curve just above the Red (ideal QPSK) perf is our modem in a AWGN
channel. Time for some math:

The energy/bit Eb = power/bit rate = S/Rb The total noise the demod sees is
No (noise power in 1Hz) multiplied by the bandwidth B, N=NoB

Re-arranging a bit we get:

SNR = S/N = EbRb/NoB

or in dB:

SNR(db) = Eb/No(dB) + 10log10(Rb/B)

Now Rb = 700, B = 3000 Hz (for SNR in a 3000Hz bandwidth) so we get:

SNR = Eb/No - 6.3

Now, say we need a BER of 2% or 0.02 for speech, the lower blue curve says
we need an Eb/No = 4dB, so we get:

SNR = 4 - 6.3 = -2.3dB

So if the modem is working down to "just" 0dB we are about 2dB worse than
theoretical. This is due to the extra bandwidth taken by the pilot symbols
(which translates to 1.5dB) and some implementation loss in the sync
algorithms, and non linearities in the system.

I thought it worth explaining this a little more. These skills will be just
as important to Hams of the 21st century as Ohms law was in the 20th.

Cheers,

David

ham radio.

Post by Helmut
The old R&S RMS-Powermeter with a tru-sensor provides a nominal accuracy of
+/- 5 %. A PEP- module for this RMS meter offers similar accuracy for
sinusoidal waveforms. From time to time I check the R&S meter with my
(old) HP 435A and a reference circuit.
The most accurate test equipment is finally my HPSDR setup. The
feedback loop for the pre-distortion delivers an exact and well
defined portion of the TX power to the RX input in real-time. As the
ADC is driven to full scale or in minimum 15 dB below the failure is
within +/- 0.3 dB for average or PEP indication (total dynamic range > 120

dB).

Post by Helmut
For the exciting tests with Alfred, HB9EPU, to get a feeling how
capable freeDV at small SNRs is, I always watch the displayed spectrum
of the incoming signal. The FFT bin width is 2,93 Hz, that means that
a signal is still visible, but no longer audible after processing in the

phones.

Post by Helmut
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group)
offers a nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average
signals, IE faithfully measuring peak and PEP ? I've been involved in
this with DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73

Post by wully
Hi all
Helmut, dc6ny, and I have done some more tests yesterday. The band
starts opening again (wonderful: we always want to test 700B).
cohpsk locks quicker than the fdmdv, at least, this is the impression
we get from our experiences. Yesterday, I started to reduce my power
(measured by an LP-100A just before the antenna coupler) when txing in

700B.

Post by Helmut

Post by wully
Helmut detected the signal and I reported about my power seting: Full
drive started with 58Watts peak. Then I reduced the power to 100mW
peak (reading the quickly changing "average" of LP-100A). This was
the last setting, that I could read on the LP-100A, my relative
powerseting was at 7 out of 256. Then I reduced to 6, then to 5, to
4, to 3, to 2. After this experiment, Helmut reported, that he could
fully decode the signal at 6, but at 5 only about 50% and lower no
decoding anymore. We estimated, that setting 6 was about 50 mWatt.

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David Rowe

2015-09-24 08:31:14 UTC

Hi Helmut,

My experience is that many Hams (including myself at times!) are
unfamiliar with the digital communications concepts I discussed below,
e.g. the relationship between SNR we commonly use for SSB and Eb/No for
a given BER. This is becoming more and more relevant as the world moves
to digital modes.

The SNR estimated by FreeDV shouldn't be affected by filtering prior to
FreeDV (as long as the FreeDV carriers are not filtered).

FreeDV works out the SNR in 3kHz based on estimates of the Eb/No for
each carrier, then normalises the SNR to 3000Hz using calculations
similar to those below.

I think the algorithm stops working properly at a few dB - it's tricky
to estimate SNR from off air signals, especially at low SNRs and when
the channel is time varying, and at low symbols rates (as you get few
samples).

Cheers,

David

Post by Helmut
Hi David,
many thanks for your tutorial, but I can assure you that definitions and
terms like SNR, PSNR, C/N, NPR etc. were already known and used in the 20th
century, when the majority of the communication channels were not wireless.
We only used the term SNR for our tests as it is displayed in the freeDV
window - indeed without any dimension- but as a certain benchmark to
determine the limit of readability. I learnt that this display seems to show
only tendency, but not a fix value, as freeDV doesn't know the current
bandwidth of the used channel. We e.g. can't calculate with a standard BW of
3 kHz as we reduce BW to the absolutely necessary width to keep willful
interference of some ignorant guys out of channel.
Thanks and greetings to down under.
Helmut
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 22:16
Betreff: [Freetel-codec2] 0dB and below
Nice work on the power measurement Helmut :-)
I wanted to say a little about 0dB SNR and below operation. In the attached
plot, the lower three curves show the performance of modems in AWGN channel
- a channel that just has additive noise (like a very slow fading HF channel
or VHF).
These curves show how much energy/bit (Eb/No) we need for a certain Bit
Error Rate (BER).
The Blue curve just above the Red (ideal QPSK) perf is our modem in a AWGN
The energy/bit Eb = power/bit rate = S/Rb The total noise the demod sees is
No (noise power in 1Hz) multiplied by the bandwidth B, N=NoB
SNR = S/N = EbRb/NoB
SNR(db) = Eb/No(dB) + 10log10(Rb/B)
SNR = Eb/No - 6.3
Now, say we need a BER of 2% or 0.02 for speech, the lower blue curve says
SNR = 4 - 6.3 = -2.3dB
So if the modem is working down to "just" 0dB we are about 2dB worse than
theoretical. This is due to the extra bandwidth taken by the pilot symbols
(which translates to 1.5dB) and some implementation loss in the sync
algorithms, and non linearities in the system.
I thought it worth explaining this a little more. These skills will be just
as important to Hams of the 21st century as Ohms law was in the 20th.
Cheers,
David

ham radio.

dB).

phones.

Post by Helmut
Therefore it was amazing, that freeDV seems to produce reasonable
readability still with SNR =0 dB.
73, Helmut
p.s. No experience with AD8362. Boonton (Wireless Telecom Group)
offers a nice USB Peak Power Sensor.
-----Ursprüngliche Nachricht-----
Gesendet: Mittwoch, 23. September 2015 01:26
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode
Helmut
How well does your power meter respond to high peak to average
signals, IE faithfully measuring peak and PEP ? I've been involved in
this with DRM and DVB.
something to watch, anyway.
Maybe use a TRUPWR (R) device like the AD8362 to measure it.
73

700B.

Post by Helmut

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David Rowe

2015-09-22 23:29:34 UTC

Hi,

Wow 50mW is amazing. Once nice feature about digital voice - once you
have enough power any further increases don't help.

I have managed to get 0 BER over NVIS paths at my radios minimum power
(0.5W). It was annoying as I wanted errors but I couldn't get any!

How far apart are you and Helmut in km?

As FreeDV matures over the next few years we will see more Hams using it
even for armchair conversations. The open source API will help - very
low cost for anyone to incorporate in their SDR.

We have the pleasure of being the pioneers - like the 1920's or 1950s
(AM to SSB) all over again. These transitions only come once every 50
years. It's nice to be a part of it.

Cheers,

David

Post by wully
Hi all
Helmut, dc6ny, and I have done some more tests yesterday. The band
starts opening again (wonderful: we always want to test 700B).
As stated earlier, we never had any problem with the 700B-tuning: cohpsk
locks quicker than the fdmdv, at least, this is the impression we get
from our experiences. Yesterday, I started to reduce my power (measured
by an LP-100A just before the antenna coupler) when txing in 700B.
Helmut detected the signal and I reported about my power seting: Full
drive started with 58Watts peak. Then I reduced the power to 100mW peak
(reading the quickly changing "average" of LP-100A). This was the last
setting, that I could read on the LP-100A, my relative powerseting was
at 7 out of 256. Then I reduced to 6, then to 5, to 4, to 3, to 2. After
this experiment, Helmut reported, that he could fully decode the signal
at 6, but at 5 only about 50% and lower no decoding anymore. We
estimated, that setting 6 was about 50 mWatt.
We both are very impressed by this result!
Unfortunately, during our experiment at higher power there were some
people trying to destroy our signal: I have to say, that they were
sucessful. In this respect, the 1600 was a little less critical.
But I think that this is just a remark. Against bad guys, one can not fight.
700B is realy a very good mode. I try to convince more people, to make
experiments. but it is not so easy, because amateurs today seem to sit
in their chair and enjoy not to experiment! What a difference to what we
heard from the amateurs in the twenties!
Great, to hear, that there will be presentations in conferences!
73, hb9epu

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real

problem.

--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
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------------------------------------------------------------------------------

wully

2015-09-23 06:14:55 UTC

Hi David

I am 275 km air distance awav from Helmut (what is claimed by Google Maps).

I should be capable of measuring the power much better by gauging my sdr
TRX. When in TX, I present my TX-signal on the screen (spectrum display)
to watch the effects of predistortion. But I have been somewhat lazy
about a correct gauging. I will clean up this. Then, I can report
exactly the used power for the next 700B-experiments.

I seem to remember, that Helmut told me, not to see the signal anymore
on the spectrum, but I am not shure. He can comment on that.

I am very happy to make use of your advanced techniques! Software is the
future!

73, hb9epu, Alfred

Post by David Rowe
Hi,
Wow 50mW is amazing. Once nice feature about digital voice - once you
have enough power any further increases don't help.
I have managed to get 0 BER over NVIS paths at my radios minimum power
(0.5W). It was annoying as I wanted errors but I couldn't get any!
How far apart are you and Helmut in km?
As FreeDV matures over the next few years we will see more Hams using it
even for armchair conversations. The open source API will help - very
low cost for anyone to incorporate in their SDR.
We have the pleasure of being the pioneers - like the 1920's or 1950s
(AM to SSB) all over again. These transitions only come once every 50
years. It's nice to be a part of it.
Cheers,
David

Post by David Rowe
The CPU load is proportional to the initial freq offset estimation
bandwidth. I'm inclined to wait a little and see if this is a real

problem.

--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
----------------------------------------------------------------------
--------
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Stuart Longland

2015-09-23 07:36:56 UTC

Post by David Rowe
Wow 50mW is amazing. Once nice feature about digital voice - once you
have enough power any further increases don't help.
I have managed to get 0 BER over NVIS paths at my radios minimum power
(0.5W). It was annoying as I wanted errors but I couldn't get any!

Indeed, the biggest limit to QRP is QRM at the receiver station.

Where I am here in The Gap, I don't get a noise floor below S7 on 40m.
QRP would struggle big time. On the bicycle, some areas are fine,
others are real bad.

--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.

David Rowe

2015-09-23 07:50:06 UTC

Post by Stuart Longland
Where I am here in The Gap, I don't get a noise floor below S7 on 40m.
QRP would struggle big time. On the bicycle, some areas are fine,
others are real bad.

The urban noise floor problem needs to be fixed.

I have some ideas for DSP schemes using two (or more) receivers and
automatic cancellation. I've worked on echo cancellation before, and
this feels similar.

If anyone would like to work on this with me pls let me know.

- David

David Rowe

2015-09-15 03:08:24 UTC

Couple of new blog posts:

http://www.rowetel.com/blog/?p=4584
http://www.rowetel.com/blog/?p=4593

Cheers,

David

------------------------------------------------------------------------------

wully

2015-09-15 07:20:13 UTC

I have not noticed any problem tuning the 700B mode. I am using a narrow
filter from 700 to 2400 Hz in the SSB-passband. From the very few
experiments we could do with dc6ny we noticed, that the locking to the
700B is faster than it was with the 1600 mode (just qualitatively, not
measured).

73, hb9epu, Alfred

------------------------------------------------------------------------------

Helmut

2015-09-15 08:48:32 UTC

Hi,

I agree with Alfred and can't see any necessity for tuning. Mode 700B
provides a constant offset of 700Hz starting from zero beat and everybody
should be able to control the frequency of his radio with a deviation of
some Hz. It's also clear that the SSB channel should be at least 2400Hz wide
and the frequency response flat, i.e. no usage of equalizer, compander,
compressor etc. Where is the problem?

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: wully [mailto:***@bluewin.ch]
Gesendet: Dienstag, 15. September 2015 09:20
An: freetel-***@lists.sourceforge.net
Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode

I have not noticed any problem tuning the 700B mode. I am using a narrow
filter from 700 to 2400 Hz in the SSB-passband. From the very few
experiments we could do with dc6ny we noticed, that the locking to the
700B is faster than it was with the 1600 mode (just qualitatively, not
measured).

73, hb9epu, Alfred

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode

and there is an absence of a distinct central carrier then a couple of extra
tick marks on the FreedDV GUI showing the edges of the signal, when
correctly tuned, as well as the centre would provide easier tuning of
signals using coherent psk modes. Note this is compounded by having an even
numbers of carriers where correct tuning is with the centre tick mark
between the 7th and 8th carriers,not aligned with a carrier. It is easy to
select the mid point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

----------------------------------------------------------------------------
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David Rowe

2015-09-15 08:52:57 UTC

Hello,

I have been testing 700B on my IC7200 with a nearby FT817 connected to a
laptop running FreeDV as a test receiver.

I had to disconnect the FT817 from any antenna and put it in a separate
room, and wind back the RF gain to get good SNR results. Rx overload
and/or pick up from the leads I guess. However I managed to get a
healthy 18dB SNR on the link using FreeDV 700B.

I wound up the IC7200 power and "USB Level" (buried in am IC7200 menu)
all the way and still had a 18dB SNR. Unfortunately I am running off a
12V battery, not 13.8V, so can't get the rated 100W PEP even on SSB.
The IC7200 internal power meter is hitting 60W. An external power meter
(which has a long time constant) is reading 12W average (ie a measured
8dB peak/average).

Has anyone else experimented with SNR while hammering your PA with 700B?

The PAPR (crest factor) of 700B is just 8.5dB, which might actually be
better than analog speech, or similar to running a SSB compressor.

Thanks,

David

Post by wully
I have not noticed any problem tuning the 700B mode. I am using a narrow
filter from 700 to 2400 Hz in the SSB-passband. From the very few
experiments we could do with dc6ny we noticed, that the locking to the
700B is faster than it was with the 1600 mode (just qualitatively, not
measured).
73, hb9epu, Alfred

------------------------------------------------------------------------------

Helmut

2015-09-15 09:20:37 UTC

Hi David,

My results: PAPR Mode 700B : 8 dB (200W PEP, 31W Average)
Analog SSB without compression: PAPR 9,1 dB (200W PEP, 24W Average)

Accuracy: +/-5% (older R&S Meter)

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: David Rowe [mailto:***@rowetel.com]
Gesendet: Dienstag, 15. September 2015 10:53
An: freetel-***@lists.sourceforge.net
Betreff: [Freetel-codec2] (over) driving 700B

Hello,

I have been testing 700B on my IC7200 with a nearby FT817 connected to a
laptop running FreeDV as a test receiver.

I had to disconnect the FT817 from any antenna and put it in a separate
room, and wind back the RF gain to get good SNR results. Rx overload
and/or pick up from the leads I guess. However I managed to get a
healthy 18dB SNR on the link using FreeDV 700B.

I wound up the IC7200 power and "USB Level" (buried in am IC7200 menu)
all the way and still had a 18dB SNR. Unfortunately I am running off a
12V battery, not 13.8V, so can't get the rated 100W PEP even on SSB.
The IC7200 internal power meter is hitting 60W. An external power meter
(which has a long time constant) is reading 12W average (ie a measured
8dB peak/average).

Has anyone else experimented with SNR while hammering your PA with 700B?

The PAPR (crest factor) of 700B is just 8.5dB, which might actually be
better than analog speech, or similar to running a SSB compressor.

Thanks,

David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode

and there is an absence of a distinct central carrier then a couple of extra
tick marks on the FreedDV GUI showing the edges of the signal, when
correctly tuned, as well as the centre would provide easier tuning of
signals using coherent psk modes. Note this is compounded by having an even
numbers of carriers where correct tuning is with the centre tick mark
between the 7th and 8th carriers,not aligned with a carrier. It is easy to
select the mid point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

----------------------------------------------------------------------------
--

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David Rowe

2015-09-15 09:28:46 UTC

Thank you Helmut,

Is it possible for you to measure received SNR as you increase the drive
to your PA, for example at 6dB, how does the SNR look compared to 8dB?

Thanks,

David

Post by Helmut
Hi David,
My results: PAPR Mode 700B : 8 dB (200W PEP, 31W Average)
Analog SSB without compression: PAPR 9,1 dB (200W PEP, 24W Average)
Accuracy: +/-5% (older R&S Meter)
73, Helmut, DC6NY
-----Ursprüngliche Nachricht-----
Gesendet: Dienstag, 15. September 2015 10:53
Betreff: [Freetel-codec2] (over) driving 700B
Hello,
I have been testing 700B on my IC7200 with a nearby FT817 connected to a
laptop running FreeDV as a test receiver.
I had to disconnect the FT817 from any antenna and put it in a separate
room, and wind back the RF gain to get good SNR results. Rx overload
and/or pick up from the leads I guess. However I managed to get a
healthy 18dB SNR on the link using FreeDV 700B.
I wound up the IC7200 power and "USB Level" (buried in am IC7200 menu)
all the way and still had a 18dB SNR. Unfortunately I am running off a
12V battery, not 13.8V, so can't get the rated 100W PEP even on SSB.
The IC7200 internal power meter is hitting 60W. An external power meter
(which has a long time constant) is reading 12W average (ie a measured
8dB peak/average).
Has anyone else experimented with SNR while hammering your PA with 700B?
The PAPR (crest factor) of 700B is just 8.5dB, which might actually be
better than analog speech, or similar to running a SSB compressor.
Thanks,
David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode

and there is an absence of a distinct central carrier then a couple of extra
tick marks on the FreedDV GUI showing the edges of the signal, when
correctly tuned, as well as the centre would provide easier tuning of
signals using coherent psk modes. Note this is compounded by having an even
numbers of carriers where correct tuning is with the centre tick mark
between the 7th and 8th carriers,not aligned with a carrier. It is easy to
select the mid point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

----------------------------------------------------------------------------
--

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Helmut

2015-09-15 10:04:11 UTC

Yes it is, but it takes some time to install and calibrate my second SDR
system. I'll report. As appetizer I attached a screenshot showing the beauty
of the mode 700B signal. Excuse me for bandwidth.

73, Helmut

-----Ursprüngliche Nachricht-----
Von: David Rowe [mailto:***@rowetel.com]
Gesendet: Dienstag, 15. September 2015 11:29
An: freetel-***@lists.sourceforge.net
Betreff: Re: [Freetel-codec2] (over) driving 700B

Thank you Helmut,

Is it possible for you to measure received SNR as you increase the drive
to your PA, for example at 6dB, how does the SNR look compared to 8dB?

Thanks,

David

Post by Peter Reichelt
David and list
As tuning is more critical on the 700 mode as compared to the 1600 mode

and there is an absence of a distinct central carrier then a couple of extra
tick marks on the FreedDV GUI showing the edges of the signal, when
correctly tuned, as well as the centre would provide easier tuning of
signals using coherent psk modes. Note this is compounded by having an even
numbers of carriers where correct tuning is with the centre tick mark
between the 7th and 8th carriers,not aligned with a carrier. It is easy to
select the mid point between the wrong carrier pair.

Post by Peter Reichelt
regards
Peter VK5APR

----------------------------------------------------------------------------

Post by Helmut
--

Post by Peter Reichelt
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----------------------------------------------------------------------------

Post by Helmut
--

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Post by Helmut
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Helmut

2015-09-15 13:29:55 UTC

Hi David,

here the report of some tests this afternoon (sorry, screenshots can't be
packed more w/o heavy quality reduction). Moreover I'm not sure whether the
SNR on the FreeDV display is calibrated in dB.
First I checked the 'mean discernible signal' of mode 700B offering
reasonable readability: SNR -1 (dB?), signal in SSB channel -130 dBm,
visiable in the noise on the panadapter. I very impressive result!!!
Then I increased signal up to -123 dBm, + 7 (dB?) on freeDv display,
comfortable readability. In a further step I raised TX PEP power by 6 dB. My
calibrated S-Meter followed, while SNR display shows 5 (dB?) more. The
proven accuracy of the HPSDR S-Meter is +/- 0.5 dB. I think that's a good
compliance with the SNR show on the freeDV window.

David, I hope this quick test helps a bit.

73, Helmut

David Rowe

2015-09-15 23:57:10 UTC

Thank you Helmut, nice to have independent verification of the SNR
estimation algorithm in the cohpsk modem. The MDS results are also
quite exciting!

Would it be possible please to test the effect of FreeDV 700B SNR, when
the transmitter power amplifier is driven harder? On my simple tests
here, I couldn't drive my IC7200 hard enough to cause any problems, so I
am wondering where the limit is for 700B.

For example if the peak/average ratio of the tx signal is 4 or 6dB, what
is the SNR degradation as measured by FreeDV 700B?

Thanks,

David

Post by Helmut
Hi David,
here the report of some tests this afternoon (sorry, screenshots can't be
packed more w/o heavy quality reduction). Moreover I'm not sure whether the
SNR on the FreeDV display is calibrated in dB.
First I checked the 'mean discernible signal' of mode 700B offering
reasonable readability: SNR -1 (dB?), signal in SSB channel -130 dBm,
visiable in the noise on the panadapter. I very impressive result!!!
Then I increased signal up to -123 dBm, + 7 (dB?) on freeDv display,
comfortable readability. In a further step I raised TX PEP power by 6 dB. My
calibrated S-Meter followed, while SNR display shows 5 (dB?) more. The
proven accuracy of the HPSDR S-Meter is +/- 0.5 dB. I think that's a good
compliance with the SNR show on the freeDV window.
David, I hope this quick test helps a bit.
73, Helmut
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glen english

2015-09-16 05:08:47 UTC

Hi David
My experience with low SNR high PAPR OFDM systems , say around 3-4.5dB
SNR requirement, is that the signal can be driven into a wall before
the SNR reduction causes an issue- the spectral splatter is a big
problem first before the SNR deteriorates to affect the performance...

But that depends on the behaviour of PAs. For PAs that exhibit a high
degree of incidental phase when compressed heavily, that may upset it.

glen.

Post by David Rowe
Thank you Helmut, nice to have independent verification of the SNR
estimation algorithm in the cohpsk modem. The MDS results are also
quite exciting!
Would it be possible please to test the effect of FreeDV 700B SNR, when
the transmitter power amplifier is driven harder? On my simple tests
here, I couldn't drive my IC7200 hard enough to cause any problems, so I
am wondering where the limit is for 700B.
For example if the peak/average ratio of the tx signal is 4 or 6dB, what
is the SNR degradation as measured by FreeDV 700B?
Thanks,
David

Helmut

2015-09-16 06:49:03 UTC