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Thanks Dave! Do you mean that RX_BPF_SEL does not change state?

Can you point me to the source of the 66.4 code you're running? I want to try to figure out why this is the case.

On Tuesday, March 25th, 2025 at 9:48 AM, D Solt via <davesolt=[email protected]> wrote:

In ver 50.0 in SSB and CW modes, TX_BPF_SEL and TR_BPF_SEL both switch states when PTT or Key engaged

In ver 66.4 in CW mode, TX_BPF_SEL and TR_BPF_SEL both switch states when Key engaged. In SSB mode, only TX_BPF_SEL switches state.

I am going to sweep the RX and TX paths to try to find blown MASWSS0179's

dave, n3ds

On Tue, Mar 25, 2025 at 6:44?AM Oliver KI3P via <oliver=[email protected]> wrote:

By comparing your final plot (Isolation PA Out to PA In, LPF Cntl SN1, 25 MHz SSB, ver 50.0) to the plot of the same configuration with oscillating software loaded (Isolation PA Out to PA In, LPF Cntl SN1, 25 MHz SSB, ver 66.4), we see that the isolation is different between these two versions even though they have nominally identical configurations. Are you able to probe the control signals on the LPF board to see how they might differ?

I did notice that the Ver 66.4 CW isolation (which does not oscillate, IIRC) is identical to the Ver 50.0 SSB isolation (which also does not oscillate). So that is the configuration we should be seeking to replicate.

Regardless, the isolation is a lot worse than it should be, regardless of the configuration. Something is not right. We should expect about 48 dB of isolation from the MASWSS0179 switch alone:

This makes it seem like the TR switch is not working -- we should measure the TR switch performance on its own outside of the control board circuit.

On Monday, March 24th, 2025 at 3:55 PM, D Solt via <davesolt=[email protected]> wrote:

I ran some isolation tests today. Below is the first page of my report (attached).

I have had an oscillation at ~35MHz in the K9HZ 20-watt power amp in my T41 V12 (SW ver 66.4) when I press PTT in the higher bands. It appears to be caused by low isolation between the PA Output, J8 and PA Input, J7, on the LPF-Control board. Below are several plots from my NanoVNA showing the isolation between 21MHz and 25MHz. On my two systems, the feedback oscillations only occur above 22MHz.

The first plot shows the isolation with C18 removed from the PCB. This capacitor is the path between the transmit and receive RF switching circuits on the LPF-Control board. So is C7, but I didn’t bother removing that. Isolation is better than 65dB with C18 removed.

The next two plots show the isolation at 25MHz in the CW mode (key down) and SSB mode (PTT) engaged. Isolation is in the 35dB range. Additionally, the poor return loss in the SSB mode indicates that the LPF is not being connected properly.

The next plot shows isolation at 50MHz in SSB mode with PTT engaged. This is so bad (<25dB) that I must have a bad RF switch.

The final two plots are done with version 50.0 at 21 and 25MHz. Performance in CW and SSB is identical.

Conclusions:

· I may have a hardware problem or a test equipment problem. Could someone else duplicate this test?

· There is a software change in how CW and SSB are controlled between version 50.0 and 66.4, but that bug doesn’t seem to affect isolation.

On Sun, Mar 23, 2025 at 7:36?AM Oliver KI3P via <oliver=[email protected]> wrote:

I found that the 25 MHz and 30 MHz bands oscillate, but the lower bands don't, matching what others have found.

To figure out why I measured the insertion loss from the output of the PA to the input of the PA. i.e., I connect port 0 of my NanoVNA to J8, and port 1 to J7. What this measures is the magnitude of the feedback loop.

What I found is that this is a lot higher than it should be, particularly at the higher bands.

| 7 MHz | 14 MHz | 21 MHz | 24 MHz | 28 MHz |
|-------|--------|--------|--------|--------|
|<-80dB | -63 dB | -53 dB | -48 dB | -47 dB |

I would expect roughly 40dB of insertion loss each through the T/R switch and the BPF selection switch U8. Clearly, I'm not getting that. It seems that the feedback amplitude is getting high enough at the higher bands to cause oscillations. What I would like to do next is:

1) Repeat this measurement for a known-good version of the code as identified by Jerry. Is this feedback path amplitude different?

2) Find the reason for the change in the feedback amplitude path by examining the LPF control signals between known-good and known-bad code.

Unfortunately, I am tied up for the week and won't be able to do this until next weekend.