ADC1 Overload

w9mdb
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ADC1 Overload

Postby w9mdb » Fri Dec 15, 2017 3:38 pm

Running WSJT-X quite successfully for a long while on < 25W.
Been testing more power and find the most I can get is about 50W and then "ADC1 Overload" in red starts showing up.

Is this the 30W limit mentioned in the manual coming into effect?

de Mike W9MDB
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Re: ADC1 Overload

Postby w-u-2-o » Fri Dec 15, 2017 7:20 pm

Mike,

The 30W limit in the manual is the thermal limit of the RF power amplifier design without any additional cooling provisions when it is used in high duty cycle operations. What exactly constitutes a "high duty cycle" is not well defined. However, 60 seconds of continuous operation such as that which occurs when using JT-65 or JT-9 probably meets that definition.

However, this has zero relationship to ADC overload. That indication is only given when the input to ADC1 is higher than it has dynamic range for. If it is occurring during JT mode transmissions (or any transmissions for that matter) it is most likely due to RFI from some part of your system impinging on the ADC1 (aka RX1) input, or inappropriate PureSignal setup.

What is your antenna setup? Which radio do you have? Are you running PureSignal?

73,

Scott
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Re: ADC1 Overload

Postby w9mdb » Fri Dec 15, 2017 8:54 pm

Should have mentions I'm using FT8 right now so just 15-second intervals...

No Pure Signal.
ADC1 overloads with the combination of VAC1 TX Gain and Power Level from WSJT-X. So if I drop WSJT-X's power level and increase TX Gain I get the ADC1 indicator agai at the same power level. I assume when the ADC1 message is red is worse than when it's yellow.

Should I be able to get 100W without overloading the ADC?

de Mike W9MDB
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Re: ADC1 Overload

Postby w-u-2-o » Fri Dec 15, 2017 10:42 pm

Minor tangent: A single FT8 sequence at 100W would be very unlikely to overheat the radio. However a number of them in quick succession might.

Back on point. The methodology to correctly set gain and drive settings in openHPSDR architecture radios is a little different than it is in more conventional radios. This is because the RF Drive control actually controls the DAC output level, the TX RF gain after the DAC is fixed, and therefore the entire headroom of the amplifier is always available regardless of the RF Drive setting.

1. You should run 0dB TX gain and no TX processing at all in PowerSDR. It's easy to do that, just select DIGU and all processing will automatically disabled.

2. Also set the audio drive level in WSJT-X to maximum. This, combined with (1) above, will ensure that audio drive is exactly at the 0dB level, and, most importantly, not over that level.

3. Using the TUNE button in WSJT-X, set your PowerSDR RF Drive control to obtain the power output you want. Since you set your audio drive to 0dB in (1) and (2) above, this will ensure that the entire DAC dynamic range is always utilized, and thereby obtain the cleanest drive signal into the amplifier possible (all DAC bits used, not just a few of them).

This should work at any RF Drive level. If you still have ADC overload indications, then there is either some sort of RFI in your station or there is something wrong with your radio. In both cases the problem can be "band-aided" by setting the radio to switch in some amount of Step Attenuator during TX.

You never said what kind of antenna you were using?

73,

Scott
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Re: ADC1 Overload

Postby w9mdb » Fri Dec 15, 2017 11:48 pm

I've got two transmit antennas. One 61ft dipole in my attic on a tuner and a 15M vertical delta loop outside that I'm testing right now.

If I set 0dB on VAC1 TX Gain the most I can get is 25W out.

I do notice that on the virtual cable control panel it appears that the level meter doesn't go very high (3rd bar) so maybe that's the problem?
Is there some was to see what signal is coming in to PowerSDR since I assume it should be a full signed 16-bit value close to 32767 maximum?

If I capture the output audio channel on another instance of WSJT-X I see a waveform of -.7V to +.7V.
I went back into the PA Gain and started turning down the Gain By Band and around 50W I started seeing ADC1 Overload again.
I had already calibrated my rig but I'll do that again I guess -- ANAN100.

If I record in PowerSDR the captured wav shows -0.5V to +0.5V

de Mike W9MDB
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Re: ADC1 Overload

Postby w-u-2-o » Sat Dec 16, 2017 2:45 am

The "voltage" readings are academic and not really of interest.

Select DIGU. Select a VAC TX gain of 0dB. Switch your TX Meter to Mic. With the level control in WSJT-X set to max., hitting the WSJT-X TUNE button should result in a Mic Level of 0dB exactly. If it does not, then there is something wrong with the VAC device setup (assuming you are using Muzychenko VAC). Make sure all VAC devices for both playback and recording are set to 48KHz, stereo, 16 bit, maximum level in the Windows Sound Control Panel. Make sure that all relevant Windows Mixer levels are at max.

Once you solve that audio level problem, then you must calibrate the radio for TX power. This is done with TUN in PowerSDR. Calibrate first at 50W, just to be safe, then at 100W. Note that the RF Drive level control is not linear. It will only be accurate at the level you have calibrated it. So if you calibrate at 100W and then try 50W and you see only 40W (for example) on the power meter, this is, unfortunately, normal. The good news is that it is reasonably linear when measured in dB, and can generally be expected to be linear within +/-1dB (understand that 50W + 1dB is 63W, 50W - 1dB is 40W.

Once you've got the audio levels correct, and the calibration correct, then you should be able to have WSJT-X drive the radio to whatever power level you have selected on the RF Drive control without fussing with any audio gain settings.

More to the point of your ADC overload: how are you antennas attached to the radio, and what kind of VSWRs are you getting? If you have a lot of reverse power on TX that can cause an RFI condition. If you are transmitting on one antenna and receiving on another that can also cause a problem.

73,

Scott
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Re: ADC1 Overload

Postby w9mdb » Sat Dec 16, 2017 4:57 am

2 channel 48kHz on the line
TX Gain=0 and MIC shows -6dB on the scale.

So I guess that means something in the audio chain....I'm using Muzychenko's VAC. I'll try another....

de Mike W9MDB
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Re: ADC1 Overload

Postby w9mdb » Sat Dec 16, 2017 5:00 am

VSWR varies by band but typically around 1.2 on the bands using now.
I do have a receive only antenna on Rx 2. I'll test with that yanked out too but that shouldn't cause a change in output power level, should it?
de MIke W9MDB
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Re: ADC1 Overload

Postby DL2XY » Sat Dec 16, 2017 10:58 am

Mike,

did you check the "ATT on TX" setting?

73 Walter
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Re: ADC1 Overload

Postby w-u-2-o » Sat Dec 16, 2017 12:04 pm

w9mdb wrote:VSWR varies by band but typically around 1.2 on the bands using now.
I do have a receive only antenna on Rx 2. I'll test with that yanked out too but that shouldn't cause a change in output power level, should it?
de MIke W9MDB

No, it will not affect output power level, but it very well might be the source of your ADC overload. This is an ANAN-100 or 100D? You had said 100, but double checking.

In the meantime you have a level problem with Muzychhenko VAC. Turn on "Stereo" in VAC setup if it's not already on, not sure if that will help, but it won't hurt.
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Re: ADC1 Overload

Postby K9RX » Sat Dec 16, 2017 2:03 pm

Mike,

you mention an antenna connected to ADC2. Are you sure its ADC1 and not 2 that is showing the overload?! If you have ADC2 set so that its not grounded on TX it can be overloaded.

Note I don't think there's anything "special" about DIG mode re ADC1 overload. Its transmit period that would cause it - are you seeing it on SSB peaks and/or on CW?

Gary
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Re: ADC1 Overload

Postby w9mdb » Tue Dec 19, 2017 2:24 pm

I figured this out. I had the audio output channel in Windows set to 1-channel instead of 2.
So I guess those two channels are added together instead of averaged. Not sure why one would need to do that in the digital realm but I guess some may be using analog connections? Even the I assume it's being converted to a float so averaging would still work and then it wouldn't matter if input is 1 or 2 channel.

de Mike W9MDB
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Re: ADC1 Overload

Postby K9RX » Tue Dec 19, 2017 3:34 pm

Mike,

HUH? How would a Windows setting play in to ADC1 overload?!

Gary
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Re: ADC1 Overload

Postby w9mdb » Tue Dec 19, 2017 3:41 pm

What apparently is happening is that using only 1 channel only gives PowerSDR half-value data.
So...50W is as much as can be put out without overdriving the ADC,
Once I enabled 2-channel power output doubled.

de Mike W9MDB
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Re: ADC1 Overload

Postby w-u-2-o » Tue Dec 19, 2017 4:32 pm

That's not exactly correct. The standard among most digi mode software is to use the left channel only for audio. If you use something like Fldigi or WSJT-X, they only put out audio on the left channel. It will be correctly carried by a single channel audio device, for instance a single VAC mono cable. So that is not the root cause of your problem.

If you are using a stereo virtual cable pair, and have PowerSDR set up for stereo in VAC, this will work fine. Setting a 0dB level in the digi app will resolve as a 0dB level in PowerSDR. If you are using a mono cable then you need to set VAC to mono.

Where you are more likely to accidentally screw it up is when using VAC for phone. The various software applications, including Windows itself and app's like Voicemeeter Banana, will often default to stereo, and that causes your voice audio to be duplicated on both the left and right channels, thereby resulting in a 6dB increase in drive even though you've got everything set to 0dB, because PowerSDR will add both channels together when set for stereo.

If you add two audio channels carrying the exact same information, in phase, together, then you will get a 6dB increase in audio level (it's a voltage thing, not a power thing). If you ever see a +6dB discrepancy in your audio, it is inevitably caused by the left and right channels being summed somewhere in your sound system, real or virtual.

73,

Scott
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Re: ADC1 Overload

Postby w9mdb » Tue Dec 19, 2017 5:10 pm

I didn't have the Stereo checked in PowerSDR. So PowerSdr seems to be summing for Mono also.

If I change WSJT-X's audio to Left channel I see the 6dB drop. In Mono it goes back up 6dB.

If I turn on Stereo in PowerSDR then both show 0dB for either Mono or Left in WSJT-X. i.e.no change.

Does this sound right?

de Mike W9MDB
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Re: ADC1 Overload

Postby w-u-2-o » Tue Dec 19, 2017 5:50 pm

Sounds perfect, Mike. And now you are aware of these little gotcha's where audio levels are concerned. :)

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