Re: QMX SWR measurement is not correct while using with PA
Correction:? You also need to know the phase difference between the voltage and current.? That's why you need two oscilloscope channels.
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>? If you find the magnitude of the voltage? and the current at the amp input port
>? using a two channel oscilloscope? and a series resistor to help measure the current,
<? then you have all the information you need to compute the complex impedance and the swr.?
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On Sat, May 24, 2025 at 11:17 AM, Jerry Gaffke wrote:
If you find the magnitude of the voltage? and the current at the amp input port using a two channel oscilloscope and a series resistor to help measure the current, then you have all the information you need to compute the complex impedance and the swr.?
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Re: Solder pot for toroid leads
I wantched a youtube on the "$20 Amazon solder pot" and it looks like he had to fill the solder pot with almost a complete 1 lb(?) bar of solder, which seems to be about $30.
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So, I went looking a bit more and I found some google articles on building a small solder pot using a spare soldering iron (I know we all have those) and using a copper or brass cap with a copper bolt thru it. As a proof of concept, I built one. Cost for a new 25 watt Harbor Freight soldering iron and the brass cap and screw was about $9. The small cap obviously requires a much smaller amount of solder (than the 1 lb bar). I tried it on some extra wire and it seemed to work fine.
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I've wound toxoids before and used the scrape the wire and then blob on soldering iron tip before, but I never felt 100% that scrapping the wire was a bit of a pain.
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Time will tell if I actually use my small soldering pot or the scrap/blob method.
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Thanks for everyone's help.
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Roy de K2RMA
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Re: QMX SWR measurement is not correct while using with PA
Petrov,
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If you find the magnitude of the voltage? and the current at the amp input port using a two channel oscilloscope and a series resistor to help measure the current, then you have all the information you need to compute the complex impedance and the swr.? However the gates of the FET's present a non-linear load, the harmonics resulting from that will be seen at the input to the amp making this business of measuring amplitude and phase of the voltage and current problematic.? It could be argued that an SWR value for a non-linear load is undefined.? Many amps include a resistive attenuator to make the input look more like 50 ohms resistive, at the expense of reducing power available at the gates.? If interested in the many ways of measuring SWR and the math behind it, see my old thread at /g/BITX20/topic/94794749
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Jerry, KE7ER
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On Fri, May 23, 2025 at 11:24 PM, Petrov Sergey wrote:
Yes, looks like it is not correct to use Nano VNA for impedance measurement for PA. Thank you! Is it possible to measure imaginary and real part of impedance for PA in some other way?
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Re: QMX+ SSB audio distorted on one band only
I have a 20-10m QMX which I ran beta SSB firmware on. 20m wouldn't calibrate, but I tried Ellis Simon's band edge and band centre values and then the rig calibrated fine.
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I've just upgraded the firmware to 1.02 and I've hit the same problem of the 20m band not wanting to calibrate. I was a bit out of the loop but my rig was initially acting weird after the firmware update, I think I'd read somewhere about having to do a factory reset, but maybe I dreamt that, anyway, after a firmware reset, the rig now works fine. I figured after the factory reset, I'd have to do a recalibration.
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I'd like to try the different band edge / centre settings as I did before, but unfortunately the group has stripped the screen shot of the settings.
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Can anyone please share 20m band settings that worked for them?
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Thank you.
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Colin
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Dean,
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there is a fault in the SWR tune function (until now). If you start the SWR tune function your last VFO frequency is shown but a per band default frequency is used. Please rotate the frequency encoder to see the real frequency and tune to your wanted f.
As far as I know this problem is on Hans list.
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73 Ludwig
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Re: QMX won't start after firmware update to 1_02_000
Power down by removing the power plug. Then see if it will power up normally.?
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Stan, thanks for your answer.
Hans the creator hopefully sorts this firmware thing out one of these days (hint hint :))
Ari OH9VL
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Thank you Roger!!
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I was surprised to see the results into a dummy load so I went back to the original configuration and back to the same problem. So just curious to see my wattage I inserted a Barb-A-Watt meter in line. Now no problem with a fault.
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I guess it was a bit of rfi on the coax tripping the SWR protection. Simple solutions to simple problems.
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Thanks again, Dean
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So i would suspect the antenna/tuner to have an intermittent connection of some sort, or to be inadequate in some way.
Roger
Get
Roger,
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I just checked and the SWR protection never faulted into a dummy load. Full 4.9 watts on all bands.
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Dean
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Obtained and replaced Q516. Diagnostics now pass Tx Bias. Stable current, all green.
More testing tomorrow.
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Thanks for this group, helped me to track down the issue.
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Roger,
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I just checked and the SWR protection never faulted into a dummy load. Full 4.9 watts on all bands.
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Dean
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Stan,
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If I understand you correct, QMX + RIT and N1MM won't be a happy marriage by design.
The RIT switch off issue in RUN mode is kind of weird.
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Anyway, it is a great contest radio. Enjoying it at the moment in the WPX contest where propagation could have been better.
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73,
Roelof, pa0rdty
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Does this happen into a dummy load?
73 Roger 8P6RX?
Get
This seems to be a complex problem because I do not understand what is happening. I will try to explain as best as I can.
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QMX mid bands built for 12 volts and Z-11 Pro auto tuner.
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I start on 40 meters and go to hardware then SWR tune and start the tune. The tuner light move and ends when a <1.5 SWR is reached. I then go to iambic and send CW at about 20 wpm. After about 10 dits the tuner jumps up to over 4 and the S protection letter shows on the screen after the last number. I cycle the menu, go to hardware, SWR tune and it shows <1.5 SWR. I go back to normal CW and the same pattern shows up again.
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It happens on multiple bands and is frustrating because I can't complete a POTA contact let alone a ragchew.
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My sBITx is also low power 1 - 4? watts and does not do this action with the tuner.
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Any ideas where to look?
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73, Dean/ N2TNN
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This seems to be a complex problem because I do not understand what is happening. I will try to explain as best as I can.
?
QMX mid bands built for 12 volts and Z-11 Pro auto tuner.
?
I start on 40 meters and go to hardware then SWR tune and start the tune. The tuner light move and ends when a <1.5 SWR is reached. I then go to iambic and send CW at about 20 wpm. After about 10 dits the tuner jumps up to over 4 and the S protection letter shows on the screen after the last number. I cycle the menu, go to hardware, SWR tune and it shows <1.5 SWR. I go back to normal CW and the same pattern shows up again.
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It happens on multiple bands and is frustrating because I can't complete a POTA contact let alone a ragchew.
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My sBITx is also low power 1 - 4? watts and does not do this action with the tuner.
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Any ideas where to look?
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73, Dean/ N2TNN
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Re: QMX+ firmware feature request
Would having the SWR sweep on the QMX display satisfy your need?
I asked Hans for this a while back but I'm not sure if he read my request (busy guy).
It seems that SWR sweep is the only terminal mode feature that is not available on the QMX display.
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Hopefully, one of these ideas makes it onto his TBD list.
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73, Mike KK7ER
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Re: R520 Wrong component value.
I may have the same issue with my QMX+. It enters Safe Mode as soon as the key is pressed on 80m and 60m. The 40m and 30m bands work fine, although 40m and 20m have nearly zero power output, which I still need to troubleshoot. If SWR protection is disabled, the QMX+ will transmit on 80m, 40m, and 20m, but power output remains negligible on these bands. However, 30m and 60m output 5W. These test were performed transmitting into a Bird dummy load
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When using the diagnostic SWR check I get 80m SWR 10, 60m SWR 10, 40m SWR 10, 30m SWR 10, 20m SWR 3.3. Not sure what 10 means, is this 1:1 or 10:1 SWR?
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Dave
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Hi Ari, currently you can leave CW wide open with a bandwidth of about 2700, or select any of several filters of 500Hz and narrower to 50Hz.? Nothing between 500Hz and wide open - that would indeed require a firmware mod, unless you use an external filter.
Stan KC7XE?
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Ah, so it does!? I was coming from the perspective of adding the AGC to a rev 1 QCX+ and having all the extra wires.
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Yours is so neatly constructed that I missed it!
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73, Mike KK7ER
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Re: 50 Watt Power Amplifier - Low Power, High Harmonics
#50w
#50wpa
The 'scope traces from your archive of the K0IKR post do resemble the issue I am having - if anything, my gate signals look a little more balanced than what he had happening.
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I didn't keep a note of it but I believe I tried running up the bias to see if that improved power output - something to try today, checkingthe waveform at T3 to see if it gets better.
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I have one of those "component guesser" testers that identify a lot of things and give a little graphic of the device symbol with some measurements made at unknown test conditions. I've only ever used this as a "go -no go" function tester - I wonder if the? parameters it measures would be an adequate representation of the device's performance in the amplifier? If they match on the tester, will they be good enough for the amplifier?? Alternatively, I can do a breadboard experiment and measure the threshold voltage the hard way - lots of multimeters!
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The other idea that came to me at 3 AM today was if my winding of the binocular core was careless, perhaps too much leakage inductance?? However, looking at my T3 and the illustration in the instruction manual shows a similar amount of windings visible at the end - it's not like I've got a 5 mm gap between the end turn and the core.
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So, my next steps are:
- Observe T3 waveform at 100 mA bias
- Order a half-dozen IRF510s from DigiKey - and hope they don't get lost in our impending postal strike.
- Sort through the new IRF510s and pick a pair with the closest match, try them out.
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I was relieved to find I could remove and reinstall the board without losing the silicone pads - I had feared this was a one-way-only assembly.
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Thanks for your tips and the archived photos!
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Bill
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Re: Release of version 2.0 of ABS solution for QMX+ (Automatic internal antenna tuner, internal battery and internal speaker with audio amp)
#PSU
#QMXplus
#audio
#ABS
#ATU
Please include me for a US based group buy.
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-Dj, N1JOV
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Roy Ashkenaz
W6MQI
Dj Merrill