Guidelines For Best Transmitted Signal Quality With Digi Modes

User avatar
w-u-2-o
Posts: 1172
Joined: Fri Mar 10, 2017 1:47 pm

Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w-u-2-o » Sat Feb 17, 2018 2:52 pm

1. Follow the guidelines here to ensure that you are "48KHz clean" throughout all of your audio setttings:

https://apache-labs.com/community/viewtopic.php?f=13&t=2655

2. Always use DIGU or DIGL (almost always DIGU except for you RTTY types ;) ). This will automatically remove all of the audio processing stages from the audio path, thereby ensuring a clean and un-distorted digi mode waveform.

3. Keep your ALC < 0dB. -1dB is fine. The ALC is an awesome, look-ahead, intelligent soft limiting algorithm, but you don't want or need any compression of your digi mode signal, as in this case compression = distortion. This is as opposed to phone operations, where the compression offered by the ALC may be seen as a desirable feature.

4. Contrary to what is recommended for conventional radios, always set your audio drive level from your digi mode software (WSJT-X, Fldigi, etc.) to -1dB, then set your desired RF output power level with the Drive slider. This is backwards from conventional rigs because in the ANAN series radios the gain in the PA and driver sections is fixed and therefore the entire dynamic range of the amp is always available. The Drive slider merely controls the output from the DAC into the fixed gain of the driver amp and PA sections.

5. Use the Single Calibrate mode of PureSignal to set your linearization prior to commencing operations. I.e. once you have your RF drive where you want it (using "tune" in WSJT-X or Fldigi, for example), use the two-tone feature (set to use drive power) and click the Single Calibrate button a few times until you get a good solution. Be sure to use DUP mode on the panadapter so you can see what is actually being transmitted for IMD. Note that the reason you can't use the automatic mode is because you are not hitting 0dB ALC where PureSignal kicks off automatic measurements, and also because the digi mode waveforms are not kind to the automatic algorithm.

6. If you are not working an entire sub-band a la FT8, i.e. if you know you are always going to center up on the 1500Hz sweet spot and then work a PSK, Olivia or RTTY signal or the like, then set your transmit passband to match your transmitted waveform bandwidth.

Do all of the above and you'll have a squeaky clean digi mode signal.

Special note: you will see noise "bursts" on the waterfall when digital modulations switch instantaneously from one tone to the next. This is normal and is a side effect of the FFT process used to display the panadapter and waterfall. These are particularly evident and noticeable when using one-tone-at-a-time modes like JT and FT modes. There is generally no need for concern about this.
w9mdb
Posts: 57
Joined: Sun Apr 09, 2017 5:53 pm

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w9mdb » Sat Feb 17, 2018 3:50 pm

Thanks a lot for posting this....

Couple questions
#1 Where is the ALC setting?
#2 Where is the "Single Calibrate mode of PureSignal"?

I'm probably blind but can't find either of these.

de Mike W9MDB
User avatar
w-u-2-o
Posts: 1172
Joined: Fri Mar 10, 2017 1:47 pm

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w-u-2-o » Sat Feb 17, 2018 4:09 pm

w9mdb wrote:Thanks a lot for posting this....

Couple questions
#1 Where is the ALC setting?
There is no ALC control per se. Switch the meter to ALC during transmit. Adjust the audio drive level from your digi mode program upwards until you see -1dB. There are many ways to adjust the audio drive level. In some digi mode programs there is an adjustment right in the program. Depending on what sort of virtual audio cable software you are using there may be adjustments in that software and the Windows Mixer may also be involved. In PowerSDR you can adjust VAC TX gain. My recommendation is to set everything to 0dB (usually the maximum setting), then back off the digi mode program control, if available, by 1dB. If not available there, then back off VAC TX gain by 1dB. This keeps things obvious and avoids potential confusion because it is easy to forget about hidden Windows and VAC software settings.
#2 Where is the "Single Calibrate mode of PureSignal"?
When you click on the Linearity menu the PureSignal control window opens. You will see a button that says "Single Calibrate". If you hit that button PureSignal makes a single calibration and the PS-A button goes dark. To get back to automatic use the PS-A button.
w9mdb
Posts: 57
Joined: Sun Apr 09, 2017 5:53 pm

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w9mdb » Sat Feb 17, 2018 4:46 pm

Couple more questions.
What is a "good solution" for Single Calibrate? How does one know?

And I guess the "Correcting" means Pure SIgnal is doing it's thing?

Is this appropriate then for all digital modes?

I'm showing the highest harmonic 50dB down on an FT8 tranmissions which sounds pretty good.

de Mike W9MDB
User avatar
w-u-2-o
Posts: 1172
Joined: Fri Mar 10, 2017 1:47 pm

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w-u-2-o » Sat Feb 17, 2018 5:05 pm

w9mdb wrote:Couple more questions.
What is a "good solution" for Single Calibrate? How does one know?
In DUP mode look at your IMD products. If the close in ones are down -50dB or more, then it is good.
And I guess the "Correcting" means Pure SIgnal is doing it's thing?
Yes.
Is this appropriate then for all digital modes?
IMHO, yes.
I'm showing the highest harmonic 50dB down on an FT8 tranmissions which sounds pretty good.
If that's in DUP display mode, then it sure does.
User avatar
Tony EI7BMB
Posts: 164
Joined: Sun Apr 09, 2017 2:31 pm
Location: Dublin
Contact:

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby Tony EI7BMB » Mon Jul 09, 2018 7:39 pm

Just curious as to what guys generally set the level of RX1 AF to when using WSJT X for best signal to noise ratio on receive ?
Last edited by Tony EI7BMB on Mon Jul 09, 2018 9:42 pm, edited 1 time in total.
User avatar
w-u-2-o
Posts: 1172
Joined: Fri Mar 10, 2017 1:47 pm

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby w-u-2-o » Mon Jul 09, 2018 8:00 pm

Great question, Tony, but perhaps worthy of it's own topic, since this one is about transmitted signal quality, not received signal quality. Would you mind starting another topic, please?
User avatar
Tony EI7BMB
Posts: 164
Joined: Sun Apr 09, 2017 2:31 pm
Location: Dublin
Contact:

Re: Guidelines For Best Transmitted Signal Quality With Digi Modes

Postby Tony EI7BMB » Mon Jul 09, 2018 9:34 pm

You are right Scott, it does not sit well with this topic on reflection. I'll start a new one.

Return to “Digital Mode & Logging Software”