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Hello;
A newbie to QMX question. Will AGC be added to QMX functions in the near future? Also sidetone volume? I¡¯m a long time CW op and those 2 functions would go a long way.
Thanks and ¡®73
Jim WX8J
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Yes for both. Many people pointed out those things. I think Hans is working on those.
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Until AGC is available, it's best to avoid headphones to avoid hearing damage. I use an Oonts Angle speaker, setting the QMX volume to the minimum and using the speaker's volume controls. I have tinnitus and I really felt one blast from this rig.?
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Good advice! I had the blast in my phones as you did. I too have had tinnitus for 50 years. Too much time in front of an elementary band! ¡®73
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On Oct 22, 2023, at 8:56 AM, K9NUD-Steve <k9nud@...> wrote:
?Until AGC is available, it's best to avoid headphones to avoid hearing damage. I use an Oonts Angle speaker, setting the QMX volume to the minimum and using the speaker's volume controls. I have tinnitus and I really felt one blast from this rig.?
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I'm ok with keeping one hand on the volume but I did think about making a simple passive AGC circuit. If I use a LND150 (depletion + enhancement mode MOSFET, normally halfway on when VGS=0V) and a Schottky diode to make a passive AF shunt AGC, I just need a simple audio amp to complete the whole thing. It's similar to QCX AGC module but the gate bias circuit becomes unnecessary.
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After nearly blowing my ear drums, I'm successfully using two?reverse-parallel silicon switching diodes as described here.?
I assume that the implementation of the AGC in the firmware is a lot more difficult than assumed, otherwise we would surely have it already....
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> I assume that the implementation of the AGC in the firmware >? is a lot more difficult than assumed, otherwise we would?
> surely have it already....
Negative, Simon. It's just that I have been a lot more busy than you assumed, otherwise you would surely have it already.
After nearly blowing my ear drums, I'm successfully using two?reverse-parallel silicon switching diodes as described here.?
I assume that the implementation of the AGC in the firmware is a lot more difficult than assumed, otherwise we would surely have it already....
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Simon,
Thanks for the suggestion. I just implemented the diode 'fix' for the lack of AGC. It's not perfect, but it works well enough for me to go back to actually using my QMX. I'm hoping to use it for an upcoming trip and some SOTA/POTA activations.?
--
73, Dan? NM3A
There are moments when everything turns out right .... Don't let them alarm you; they pass.?
-Jules Renard
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Dan,
Did you try this with one diode in each direction first, and then decide to double up based on the results - or just go large from the start?
I'm curious about the difference between one pair vs two.
Tnx &,72.
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I did one POTA activation with my QMX when I got it working and it was great but these two features are a must.
The signals were so strong my external speaker would get very distorted (even with volume turned way down).
I'm glad I heeded the advice to not use headphones.
When AGC is implemented a nice to have feature request would be: save AGC state (on/off) by mode. AGC ON a must for CW but kind of nice to have off for FT#.
Nic
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Ted, ?I did not try a single diode. Since this is an AC audio signal, I believe you need both diodes. I used diodes I had pulled from a dead commercial circuit, but no reason why you can't use ordinary 1N4148 or equivalent. You just need to make sure they will fit in the space. You may be able to just use two between tip and ring, but I opted to use both sides to ground. I have used the QMX for MST and just tuning around and I can confirm it works well to reduce the volume peaks to non-painful levels. Large signals still overload and distort, but are tolerable until I can get the volume turned down.? -- 73, Dan? NM3A There are moments when everything turns out right .... Don't let them alarm you; they pass.?
-Jules Renard
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Hi Nic
Why is there ever a need for AGC on FT8?
On Wed, Oct 25, 2023, 5:38 AM Nic Heath < nicheath@...> wrote: I did one POTA activation with my QMX when I got it working and it was great but these two features are a must.
The signals were so strong my external speaker would get very distorted (even with volume turned way down).
I'm glad I heeded the advice to not use headphones.
When AGC is implemented a nice to have feature request would be: save AGC state (on/off) by mode. AGC ON a must for CW but kind of nice to have off for FT#.
Nic
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The QMX has higher integer precision than wsjtx uses. On a quiet band with only very weak signals present, wouldn't AGC give wsjtx more bits of signal to work with (i.e., higher SNR)?
73, Mike KK7ER?
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Hello Mike
Yes OK I see... yes true, QMX outputs 24-bit audio, but WSJT-X only consumes the most significant 16-bits. So perhaps you could argue for a slow AGC even for Digi. Certainly a lot less critical than for CW though. QMX does have a per-band gain setting, that can be used to equalize across bands for antenna, filter etc differences. I think this would normally be enough.
On Wed, Oct 25, 2023 at 8:09?AM Mike KK7ER < groupio@...> wrote: The QMX has higher integer precision than wsjtx uses. On a quiet band with only very weak signals present, wouldn't AGC give wsjtx more bits of signal to work with (i.e., higher SNR)?
73, Mike KK7ER?
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I would not use AGC for FT# or other digital narrow band signals, one strong signal on the channel ruins the rest of the incoming weak signals.
73 Ton PA0ARR
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I totally agree with Tom. I also have an Icom 7300 which is a very good radio. It has an AGC that is normally on for all modes, SSB, CW and digital. I found that turning AGC off for digital was much better for that reason. A strong signal does not hide the weak ones with AGC OFF, especially digital modes.
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I would not use AGC for FT# or other digital narrow band signals, one strong signal on the channel ruins the rest of the incoming weak signals.
73 Ton PA0ARR
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Same AGC discussion has existed among CW operators, too, especially for pileup conditions. Strong AGC is easier to operate but softer AGC or no AGC is better for picking up weaker signals adjacent to strong ones but requires adjusting RF gain all the time. Some rigs allow fine tuning of the AGC characteristics/parameters while others give just fast/slow.
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Hi all
I both agree, and disagree, and with everyone.?
I do see what Mike's saying. QMX has a 24-bit USB soundcard, and WSJT-X uses only the top 16-bits. It's a 16-bit sound device and the Windows/Linux/Mac OS will do the necessary conversion which means dropping the 8 least significant bits. If you want to be able to manage a quiet band, without losing the weak signals to those 8 least significant bits.?
On the other hand yes, having AGC means if you got a strong signal, it would cut back the gain and then those weak signals you want, could get reduced down into the noise, by going into those lowest 8 bits.?
I think really, 16 bits (as WSJT-X uses) is probably plenty for the normally observed in-band signals. FT8 works down to what, -22dB? And WSPR down to -32dB? And what's the strongest signal you ever saw? I don't think I've seen higher than?+20dB on JS8Call or WSJT-X. That's my experience, covers 52dB. But 16-bits is 96dB. So it should be easily possible to set up the gain on a band such that weak signals don't get lost and strong signals don't overload anything, and no AGC required??
96dB should be enough in-band dynamic range for WSJT-X.?
The point of a higher out-of-band dynamic range such as QMX has, is to avoid overload and intermodulation products from strong out of band signals or the summation of strong out of band signals.?
I totally agree with Tom. I also have an Icom 7300 which is a very good radio. It has an AGC that is normally on for all modes, SSB, CW and digital. I found that turning AGC off for digital was much better for that reason. A strong signal does not hide the weak ones with AGC OFF, especially digital modes.
I would not use AGC for FT# or other digital narrow band signals, one strong signal on the channel ruins the rest of the incoming weak signals.
73 Ton PA0ARR
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My impression is, we are expecting too much from a "24bit USB soundcard". The PCM1804 is a very good audio ADC, nonetheless it has a dynamic range of 112dB, equivalent to "only" 18.7bit resolution in ideal situation. This means, the lower 5 bits are all filled with noise. So its only 3bits difference to a 16bit device.And this is only if the gain of the OP amps is perfectly calibrated to match the FullScale max of the ADC, if not, it is even less than 18bit. Additionally, I have never seen an antenna situation where the noise floor is so low, that a Ham Radio signal signal is higher than 96dB above the noise. But that may be different, if your QTH is in a very low-noise situation.
So, in my opinion, it is not worth developing a software solution to match a "24dB" audio card to a 16dB WSJT-X input. But YMMV.
73 de Frank DD4WH?
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Hello Frank
It's a different thing. Firstly, the PCM1804 has a spurious-free dynamic range of 112dB. Practically, one can argue that the usable dynamic range exceeds 112dB because the spurs don't occur where we are using the response (across the bandwidth). On the other hand other components such as switching noise floor also affect the dynamic range.?
The input dynamic range is not just important for how many dB exist between the strongest ham band signal and the noise floor; but also for avoiding intermodulation from any other signals entering the receiver, out of band, including 100kW AM stations 1MHz away, for example.?
In any event? - this is the 48ksps sampling at the I and Q outputs of the QSD. This is NOT the same thing as the? demodulated SSB 24-bit audio provided to the PC over the Virtual USB sound card. You can overdrive the USB sound card by selecting a too high DSP gain; or underdrive it (pushing the signals down into the lower bits of the 24-bit range) by using a too-low gain.?
But I do agree generally, I think, that 96dB afforded by a 16-bit transfer to WSJT-X is likely sufficient for any scenario of in-band relative signal strengths. Anyway I can add AGC, for people to play with, which can be switched off of course, but I think it is not likely to be a useful thing.?
My impression is, we are expecting too much from a "24bit USB soundcard". The PCM1804 is a very good audio ADC, nonetheless it has a dynamic range of 112dB, equivalent to "only" 18.7bit resolution in ideal situation. This means, the lower 5 bits are all filled with noise. So its only 3bits difference to a 16bit device.And this is only if the gain of the OP amps is perfectly calibrated to match the FullScale max of the ADC, if not, it is even less than 18bit. Additionally, I have never seen an antenna situation where the noise floor is so low, that a Ham Radio signal signal is higher than 96dB above the noise. But that may be different, if your QTH is in a very low-noise situation.
So, in my opinion, it is not worth developing a software solution to match a "24dB" audio card to a 16dB WSJT-X input. But YMMV.
73 de Frank DD4WH?
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Ryuji Suzuki AB1WX
K9NUD-Steve
DD4WH