(tr)uSDX Forum

Hi,
I just finished the build from a kit from new diy tech. (tr)uSDX worked fine the first try. I've made 10 contacts with it and a common comment is the transmit audio is scratchy. I've monitored my audio while connected to a dummy load. The transmit audio is bad. I've changed the noise gate and Tx Drive parameters to no avail. I've used both the built in and an external mic and no difference there.

There is a YouTube video by Kevin Loughlin also describing the modulation problems. It's a great little radio, but poor transmit audio is a no go for me. Is the mic audio overdriving the Xmit RF? HELP

I'm stuck, any help?

Kindest regards,
Tim KO4ELL

Have you tried this:
https://www.youtube.com/watch?v=dHttnDdADqo

It is a response given by Manuel to Kevin's problem... ?

I'm not sure what you mean by scratchy but I found the reason for my (tr)uSDX's bad audio:
http://ae5x.blogspot.com/2022/11/video- ... rusdx.html

With 5 bands for $86, I'm happy with the rig (and recently bought a 2nd one) but I'm a CW op.

73,
John AE5X

I have the same issue with my rig. None of the suggested fixes help me. Does enabling your VOX create a lot of RX noise?

I measured the voltage going into the Atmega pin PC2 for the microphone and found the peak voltage to be around 5mv and the low around -3mv when yelling into the microphone. I suspect I shouldn't see negative voltages on that pin. Does anyone know the valid range of voltages I should see on pin PC2?

I was able to resolve my poor transmit audio. I had a bad resistor leading into the microphone input circuit. Replacing R9 resolved my poor transmit audio. If you check the voltage after c17 it should be around 0.5v. KO4ELL, you may want to check your PC2 input voltage as well and report back.

KO4ELL wrote: ↑06 Nov 2022, 14:02 Hi,
I just finished the build from a kit from new diy tech. (tr)uSDX worked fine the first try. I've made 10 contacts with it and a common comment is the transmit audio is scratchy. I've monitored my audio while connected to a dummy load. The transmit audio is bad. I've changed the noise gate and Tx Drive parameters to no avail. I've used both the built in and an external mic and no difference there.

There is a YouTube video by Kevin Loughlin also describing the modulation problems. It's a great little radio, but poor transmit audio is a no go for me. Is the mic audio overdriving the Xmit RF? HELP

I'm stuck, any help?

Kindest regards,
Tim KO4ELL

Here is a sample of my audio before and after replacing R9 on my mainboard.

Before: https://drive.google.com/file/d/1Jk2RM4 ... sp=sharing
After: https://drive.google.com/file/d/1v_0XDJ ... sp=sharing

That sounds like you didn't make the adjustment in menu 8.3

Strikingly better transmit audio!
How did you ever figure out and isolate the problem to a bad R9?
And what was wrong with it?
Tnx

Ohwenzelph wrote: ↑10 Jan 2023, 17:51 Strikingly better transmit audio!
How did you ever figure out and isolate the problem to a bad R9?
And what was wrong with it?
Tnx

I ended up loading the original uSDX firmware onto my (tr)uSDX with the DIAG flag enabled. This does some basic startup checks of the board. It was throwing an error about 0v for Vadc2 when it expected values between 3.2 and 1.8. I was able to verify the nearly 0v with a multimeter on the Atmega pin PC2. I also noticed checking resistant across R9 was giving 20k ohms instead of the expected 10k ohms. I added a 10k ohm resistor right onto of R9 in parallel and the problem went away. That gave me the confidence to remove R9 and just replace it.

I'm not sure what was wrong with it. From visual inspection it looked fine. Even after determining it was the problem re-flowing the solder had no impact. Maybe just a bad part?