Just put a common mode choke 10 feet from your rig in the antenna coax line. ?I have had RFI cause all kinds of strange interference with my experimenting with all my QRP rigs. ?I have found that a CMC at 10 feet has “cured” many strange problems I have had in the past 10 years.?

On the WSJT-X I have birdies or whatever they are, which I don't have in CW mode I do have this continuous tone over the whole band as reported before.

?

What can that be?

?

--

Martin

DK3UW

I have yet to try the K6ARK microphone that I assembled using this mic as well.? Good to know that if it isn't performing quite well enough that it might just be a swap to get better performance.? Thanks for that tidbit Erik and Stan!

?

I also have a QRPGuys mic to try out soon too.? Just finished printing a case for mine as I'm not particularly fond of a PVC fitting.

?

73,

?

Stan,

Thanks for the tip on using the QMX at 1/4 power to set the tuner after a band change. That works and now I don't get the dreaded "S" after the frequency.

?

I don't intend to use the QMX in the shack but I wanted to do something to see if it worked before I introduce more variables in the field. Probably use a Wolf River Coil in the field. I also have an EFHW to try.

?

I am learning more each day.

Jim W0RLD

Stan, as requested, here is Jeff Moore's summary of his findings on my rig that was exhibiting wildly fluctuating bias current and simultaneous fluctuating output power.

?

Jeff found under microscopic exam, that the Q516 transistor had been damaged either in manufacturing or shipping. He also found and replaced a faulty TCXO.

?

I commend Jeff (W1NC) for his amazing skill and generous support of our QRP Labs community.? For the mere price of parts, postage, and a voluntary donation so he can assist other hams, a rig sent to Jeff is returned in the best possible operating condition.

?

Here, in Jeff's words, with his permission, are his findings on my radio:

?

" ?

Here is what I found and did:

?

1) Disassembled all boards, scraped off old flux, cleaned with 99% IPA

The reason I do this on every rig is that it forces me to look closely under the microscope at every solder joint and component. ?

Often solder splashes or cold joints can be hidden by the dried up old flux.

2) Inspected under 10x - 20X microscope

Display / Control board

Nice job!

The Main PCB had no issues seen

3) Powered up at 6.1V and installed rev 27 of firmware

Factory reset - all good

The reason I use 6.1 volts is because it’s the lowest voltage that will allow the rig to operate (except for TX) and will minimize damage is something is terribly amiss.

4) Tested on bench at 6.1 V Controls, buttons, encoders, AF, image scan, A/D scan and rf scan functions - all found to be good

5) Shut down rig and increased voltage to 12v.? Tested LPF & TX functions on all bands at 12V.?

Power out fluctuated and bias current all over the place

Diagnosed to a faulty Q516 transistor - You can see a crack in it under the microscope.

Replaced Q516

Now power out is constant and bias current steady at 30ma

LPF shapes and cutoff frequencies all good

TX bias current is correct for every band (30ma)

TX power reduction (to about 1-2 watts) works well for LPF scans - This is an important test

SWR bridge works well for all bands

6) Measured minimum discernible signal on all bands - < .02 microvolts - very good

7) Measured frequency accuracy - not close to setting

Measure TCXO output - found a very odd and varying waveform

Replaced TCXO - This is a tough chip to replace

Now frequency accurate to within 1 Hz

8) Measure spectral purity on all bands - easily exceeds FCC requirements and meets QMX design goals

9) reassembled into case and retested everything one last time - now 100% RX, TX all modes, all bands

?

Total time spent - about 3 hours"

?

I hope this info sharing helps others who may encounter this bias current misbehavior.

?

?

72 and 73,

Bill? W3WJ

Ian,

I've been running my QRP rigs at 12V from a number of PD sources using multiple trigger cables, batteries and power bricks, some for up to 2 years now with no difficulties. Glad to hear you are enjoying USB-C PD.

73 Rick K8BMA

Stan,

Thank you so much for your detailed reply. You are an important part of my education.

Jim W0RLD

You and I are in the same club Bill.?

?

Jim W0RLD

Bruce,

?

I do encourage people to know what they are doing.

It's good we have this conversation to alert them of the dangers of large batteries.

?

Most of us think nothing of barrelling down the road at 70mph wrapped up in a steel cocoon

with 15 gallons of gasoline and a lead acid battery.? A battery protected by automotive fuses.

That's considerably more dangerous than anything we've discussed here.

?

I'm sure many in the forum have a lead acid battery sitting under the desk for backup power.

An LiFePO4 battery is a better choice, for both safety and performance.

I remain convinced that an automotive fuse inline with 16awg wire is sufficient

to safely power a QMX from a large 12v battery.

?

Jerry, KE7ER

?

?

?

?

Jerry Gaffke

9:38am???#143163???

Let's not get too carried away with special $150 fuses and such, that only discourages the use of these batteries.

Large high current batteries should be treated with respect, but are very useful for the amateur.

Used properly and with some understanding of what's going on, they are not dangerous.

Jerry.?
To save you any more Arc welding experiments :? The maximum breaking capacity I've ever seen quoted for ATO fuses is 1kA at 32V..? ? Which is a lot ... surprisingly so . . but in some cases, close to a battery,? not enough..

For the record I really cannot agree that safety should be put aside to encourage those less experienced (aka no idea 'what's going on') to use large battery storage without proper protective devices but it's up to you for you I guess.?
As I was saying the T fuses are the expensive way to do it properly and it's already identified that there are several better cheaper ones that also do the job safely and properly and/or even better.?

You are correct (as always), Ludwig.? I didn't think of that.

In this case I don't see any risk in removing the 3V smps, so that you can measure the voltage on PWR_HOLD without the processor intervening.

?

[Since we know that the 5V and 3V smps regulators are working, and that there is no short between +12 or VCC with VDD, then there is no risk in removing the 3.3V protection diode.]

?

Thanks for making me think outside of the box again, Ludwig.

Stan KC7XE

On Mon, Apr 14, 2025 at 02:30 PM, Jim Brown wrote:

After making several contacts on WSJT-X, the S appeared after the frequency.

I select Hardware tests/ Tune SWR and I get an SWR of 1.00 but when I transmit in WSJT-X, the S appears after the frequency and I get no output.

?

This is likely due to your use of the antenna tuner while transmitting at full power.?

When that ATU switches its relays to find a match, it presents momentary 'high SWR' to the QMX, causing it to go into SWR protect.? [Depending on your ATU, this may also happen even if it doesn't 'tune', when it switches to its tune memory settings for the current frequency.]

?

What I recommend doing is disabling the 'auto' on your ATU during normal operation, and when you change bands/frequencies and need to tune again, turn back on the 'auto', and use the QMX Hardware tests -> Tune SWR feature to give a reduced-power signal to activate the tuner auto-tune.? The SWR protect is automatically disabled in this mode, and the reduced power will remove risk of blowing your finals due to high SWR.? The default setting is 50% (voltage), 1/4 power.?? If this is too low for your tuner, turn it higher, maybe up to 75% (Protection menu -> Tune %).? This is how the QMX was designed to adjust tuning.

?

Some others don't like to do that, so they disable SWR protection, or set its threshold very high, so it won't trip when the ATU switches.? But do this at your own risk: it will likely work fine for a good while - but the momentary high SWR events may eventually wear down your finals and blow them.? There have been a few posts in this forum in the past about blown finals due to ATU switching.

?

Or just use an antenna that already has an SWR of about 1.7 or less - and don't use a tuner.? There is almost no functional difference in tuning an SWR of 1.7 down to 1.0 vs. not using a tuner.? The small loss in the tuner inductors is about the same penalty as a bit higher SWR.

?

Stan KC7XE

On Mon, Apr 14, 2025 at 01:59 PM, Jim Brown wrote:

The WSJT-X Rx max is about 50db. Normally I like to have that at about 70 db.

Is there a setting on the QMX that I can increase that?

?

Yes, you can change it using the audio level control in the Band configuration screen (via the terminal interface). It is set on a per-band basis.

But I don't think you should.? WSJT-X authors recommend 60 or below, and raising it won't improve your receive performance.

?

Stan KC7XE.

After making several contacts on WSJT-X, the S appeared after the frequency.

?

I select Hardware tests/ Tune SWR and I get an SWR of 1.00 but when I transmit in WSJT-X, the S appears after the frequency and I get no output.

Stan,

There was an S after the frequency at one point but I have eliminated it.? I have disabled the B and Split VFO. Thank you for your suggestions!

?

I removed a Heathkit Power Meter between the antenna tuner (LDG AT100proII). The antenna tuner was getting its power from my IC-7300 and there was a control cable from the 7300 as well. I disconnected the control cable. The auto tune of the antenna tuner can be activated by as little as 1w.?

?

I tried to make WSJT-X contacts again. First contact was Nova Scotia and a second Georgia on 20m. So I guess I have things working now.

?

I do have a question on the attached screenshot.

?

The WSJT-X Rx max is about 50db. Normally I like to have that at about 70 db.

?

Is there a setting on the QMX that I can increase that?

On Mon, Apr 14, 2025 at 10:27 PM, Stan Dye wrote:

PWR_HOLD is harder to measure - you may need an oscilloscope: when the QMX processor boots, within about 1/2 second it will assert the PWR_HOLD voltage high, and you want to see the voltage on it before this.

Stan, could it be there is a way without an oscilloscope? When the 3.3V SMPS is removed the controller couldn't boot and you may check PWR_HOLD using a DMM. What do you think? Is there a reason not to "start" with the 3.3V board removed, maybe a risk causedby the missing SMPS?

?

73 Ludwig

Thanks Ludwig, I must have skipped a step in the math...