Usdx+ and Digirig + Baofeng cable

I have a usdx+ radio, digirig 1.9, digirig (black) Baofeng cable. Receive works fine, RTS keys the radio upon testing from within JS8. However output power goes to max with no audio input. Testing the setup with cable plugged in a Baofeng radio, it functions perfectly. Plugging the usdx+ factory mic into the Baofeng works perfectly. Plugging a Baofeng factory mic into the usdx works perfectly. I’ve checked the wiring diagrams for usdx and digirig baofeng cable and they appear to be exactly correct. I should have zero or very low wattage out when simply keying via rts, with no audio generated. I have this exact same issue on a Trusdx with the digirig trusdx cable and digirig 1.9 at another location. I have several digirigs and have tried them on other setups and they all work fine with my anytone rigs. Scratching my head on this one as to where the max drive is coming from.

How do you trigger PTT by RTS without audio?
Usually in software it’s done with “Tune” function or similar which also sends the tone.

With Baofeng how do you know if you are sending power?

I have a watt meter in line to monitor output. In both JS8Call and Wsjtx under radio tab in settings there is a test PTT button which only keys the radio but does not send audio. I like to use that function first to look at output, before using the tune button on the main interface and adjusting audio level out to radio. On my other setups I am used to seeing the radio switch to tx mode but have no power out or maybe 1 watt when using the test ptt function. The usdx however produces full power under those conditions.

Edit: I am using the Baofeng digirig cable plugged into the k1 jack on rear of the usdx.

You can remove Digirig out of equation by just simulating the PTT - short sleeve to nearest ring on the Digirig’s side of the cable as shown here. Do you still get power on the air?

That test yielded 0.7 watts, which is the same output I get with a baofeng microphone keyed up without speaking. I get 3.1 watts keying it via the digirig (which is the same output as cw for this radio on this band). So it seems like the radio is seeing some kind of audio from the digirig, however if I unplug the cable going to usdx from the digirig and plug in the cable going to my anytone radio and do the same ptt test in wsjt there is zero audio coming from digirig. Plug usdx in and it sees audio, yet shorting the sleeve to the ring on the cable to key the usdx it behaves normally with minimal power out.

It would take a scope to see if there is some signal. Could be some artifact of digital side of things that gets filtered out by one radio but not the other. Are you using Digirig 1.9?

Yes, they are 1.9. One of them is the smaller form factor Digirig, the last one I ordered. It has a metal case, but is smaller than my other digirigs. I didn’t see it on the website but assumed it was a revised case design. I meant to ask about that as I havnt seen anything online about a smaller digirig other than the light version.

That one is 1.10 - mostly a cosmetic change but a bit more of the RF filtering. Do you get the same result with a smaller unit?

Yes. I tried two of the larger digirig and the newest smaller one and all seem the same. I also just tried connecting the usdx to a digipi with the digirigs to see if maybe the raspberry pi zerow2 might have less noise on usb bus, same results. I will test the audio circuit with a scope coming from trrs plug to bare leads connected to audio on digirig and see what is there on rts ptt with no audio from program.
I appreciate your help and advise with this.

I checked signal present across ring #1 and sleeve audio/ground in three states. First was with no ptt activation, second was with rts ptt activation without audio, third was rts ptt activation with tuning audio tone. I will attach images of the scope.

I also tried powering the digirig from my phone with a usb-c to usb-c cable and the scope results were identical.

I have seen youtube videos of people using a digirig with a trusdx (I have this same issue on a trusdx as the usdx+). That makes me curious if the noise is present but the digital audio is stronger and still transmits clear enough to work digital modes? I also think about is the noise overdriving the radio, as adjusting the tune level would have no effect if the radio is at full output upon rts ptt.

Does the noise interact with the usdx/trusdx processor in some way that other radios have no issue with? I think I will make up a cat control cable and key the radio via cat and then I have more options to bring audio in and see what happens. I can’t be the only one to run into this. If I find a definitive solution I will post it here.

Thank you for the info. I’ll be looking into it.
If systematic, this wasn’t reported before because the noise is outside of audio band and radios are likely ignore or filter it out. Do you get the same frequency and amplitude across different Digirigs?

I had tested the smaller digirig first, but I just tested the other two larger digirigs. The voltage is zero when it should be zero, and a pretty sine wave when sending a test tone. I had noticed the smaller one was warm to the touch earlier so I checked the current draw across all the digirigs and found the larger 1.9’s draw .082 amps on average and the smaller 1.10 is drawing 0.124 amps on average.

I’m thinking the smaller 1.10 digirig is defective, as it draws a lot more current, gets warm and produces noise all the time on the audio line. I will attach pics of the scope from one of the other digirigs on ptt no audio, and ptt with test tune. The usdx has the same issue with all the digirigs but it looks like I found the newest digirig is defective.

I looked into this further and I believe I found a solution, though it’s not clear why there is a problem in a first place. It’s this cap:

My models showed that it’s a good value for filtering RF while not loading AF, but somehow codec doesn’t appreciate the capacitive load and oscillates. Removing it things down:

Give it a try if this is something you are comfortable with. I’ll handle the replacement if you prefer not to deal with it or if your attempt fails in any way.

I removed the cap you circled, and ran the tests again. It is now very clean on the audio line with zero voltage present at idle. The sine wave is clean on rts ptt with audio tone. I checked the current draw and it has dropped down to normal like the other units. I am attaching scope & ammeter pics of tests after modification. Looks to me like your mod fixed the digirig. Thank you!

Thank you for confirming the fix as well as all your help diagnosing the issue.
I’ll work on correcting the current stock.

If others encounter the same issue, then the same offer stands: fix it at home if comfortable trying or I’ll replace it if not comfortable or unsuccessful.