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Hello everyone,

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I've seen in different topics that T507 solder joints should be checked & reflowed in the event of a high SWR spike on SSB transmit... a problem that several of us have mentioned, and in my case, makes the rig completely unusable on SSB. I do understand, looking at the schematic, how this could cause the protection circuit to trigger.?

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What I do not (yet) understand is why this would be a problem that I see on SSB only, and not on CW. I have not witnessed this on CW. A theory I have is that maybe if the joint is just on the edge of continuity, then a higher duty cycle CW signal would temporarily "anneal" the bad joint, but that on SSB you don't have that effect.

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I am a skeptic about my theory...in any case, I do plan on trying reflowing T507 and associated circuitry. This was a factory assembled unit so I was hoping to avoid this, but I appreciate all that Hans is doing. I'm not complaining at all... just looking for guidance and thoughts so I can get this amazing rig on SSB.

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God bless,

Joel W9JFK

It is only my (educated) opinion, but I don't think the swr 'spike' at the beginning of SSB transmission has anything to do with T507 soldering (at least if CW and Digi mode behave correctly).

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I think it is instead due to the fact that when first pressing PTT in SSB mode, there is zero (or near 0) power being output, until the microphone signal is present, and maybe firmware is not handling that as well as it should.? When there is near-zero power output, the calculation for SWR has a divide-by-zero problem, which could generate an invalid result.

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Note that pressing PTT (engaging transmit) cannot change the actual SWR - that can only be done by changing the impedance match at the BNC jack.? So this issue is just a cosmetic problem, unless it triggers SWR protect due to some false calculation.? I have never seen it trigger SWR protect on my QMXs, including during the hundreds of PTT events during my recent SSB POTA activations.

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Stan KC7XE

Stan,

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That makes a great deal of sense to me, and I would not be surprised at all of that ends up being the case. But why some, and not others observing this issue? That is a question I have. In my case, SWR protection consistently triggers in 90% of the times I engage the microphone.

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We'll figure this out eventually. I just want to have fun like everyone else LOL...

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Joel W9JFK

On Sat, May 10, 2025 at 06:55 AM, Joel W9JFK wrote:

But why some, and not others observing this issue?

Perhaps it depends upon which channel, forward or reflected, has a slightly higher noise level with no signal.?

If the forward channel has higher noise it will consistently show a lower VSWR under no-signal conditions, if the reflected has more noise it will show a higher VSWR, perhaps enough to trip the protection.??

73, Don N2VGU

Not a bad thought...makes sense.

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I did reflow all of the transformer joints pretty significantly with no impact on what I am observing, so it doesn't seem like that was the cause of the problem. Just another data point of evidence.

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Back to the drawing board!

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Joel W9JFK

This could be tested if the SSB generation could be caused to have a very small amount of carrier available, as a pilot carrier. Then there should never be a divide-by-zero (which I have no doubt that Hans will have trapped) or a divide-by-near-zero that he may not have trapped.?

just a thought.?

Hi,

I am having this problem as well but on 40m and not on 20m. Ive had no problems operating SSB on 20m since Beta 0 through 3 and just updated to production firmware with the same results.?

on 40m the SWR protection kicks in just by keying the PTT, no voice input at all. I will try re-calibration today and see if changing mic gain has any impact. This is with kit built QMX using my low SWR QTH dipole so real SWR is not the issue.?

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i would love to know what is happening so we can fix and I can try 40m. I’ll test the other bands with a dummy load.

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I’ve tried other mics but the same brand. I’ll also try digi to see if it triggers then. Not sure if it could be a mic issue.

KF0OUH

Perhaps feed a small DC current into the forward diode's output node, so that there is always a non-zero signal there, to avoid dividing by zero.

73, Don N2VGU

There are several things I'd suggest:

None of these is difficult, it's only software.

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Chris

On Sun, May 11, 2025 at 01:09 PM, Chris, G5CTH wrote:

First don't trigger the SWR protection unless the forward voltage/power is greater than some threshold.

I did exactly this, only in hardware, for my current client project's AD5519-based VSWR protection circuit.?

I wired the forward power comparator and the VSWR comparator outputs so that both needed to be satisfied to shut down the amp.? Pots adjust the power and VSWR trip points? An SCR provides a latching function when triggered

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73, Don N2VGU

Hello everyone!

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I am happy to report that although the problem with initial SWR on my QMX+ being too high, and sometimes triggering the protection, is still there, I have managed to mitigate the problem until it is addressed in firmware to make it even better.

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First, I raised the SWR protection threshold from 3 to 4. I make a special effort to pre-tune with the tune feature, and am waiting with anticipation when the firmware is edited to default to the current frequency. I realized that THIS was why the problem was worse on 80 meters than the other bands. It's because my SWR tune is much sharper on 80 than on other bands (antenna is not optimized for 80 by any means). So the tune function found the tune at the default frequency, but I could not assume that the SWR was reasonable at my actual operating frequency.

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Now, I am able to use SSB without triggering protection. The procedure I use to tune is...

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(1) Use the SWR / tune function to rough tune the band and get as close as I am able without risking finals

(2) Use a CW carrier to fine tune at the actual frequency I am on

(3) When I first start transmitting on SSB, I activate the PTT without speaking... with the safety threshold at 4, this seems to be fine. The initial SWR problem corrects, and I am able to transmit from there on out with good SWR, at least for the length of a normal QSO. If it;'s been a while since I transmitted, I quick repeat the PTT without talking step...

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With this procedure, I am getting very good SSB reports. I am using the specified Digikey mic wired up on a protoboard. I use a mic gain of 50 and a mic compression of 5. Everything else is at factory default. I have received no complaints and a few compliments on my audio.

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I also have managed to successfully integrate an old Ten Tec 405 amp to get 50 watts out, using a Pacific Antenna 11 dB variable attenuator between the rig and the amp to limit the input to result in <= 50 watts out (per the Ten Tec amp requirements). Eventually I plan on integrating the attenuator inside the amp only in the transmit chain so that it doesn't affect my receive at all.

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Just checked into the OMISS 40 meter net and waiting for my turn. A picture or two of my setup is attached here.

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I am having fun... finally LOL...

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73,

Joel W9JFK

There's a hidden diagnostic menu, start the terminal and from the main Menu type 'd'.

This shows a lot of raw data, ADC values for example and? at the top left are BIAS, FWD and REVS.

FWD and REVS seem to be the raw DAC values for the power/SWR meter, I see values of 4x FWD and 2x REVS with the QMX in Rx mode.? The x values are changing too fast to read.

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I connected a PTT and microphone, set? SSB mode, started the terminal in the 'd' mode and transmitted. With no sound FWD went to about 80 and REVS barely changed.? With sound FWD went to 1000 or so and REVS to about 80.? This is all with a dummy load so as expected.

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I wonder what values a system that's prone to the SWR trigger will show.

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Chris