Re: QMX Loud Noise on Boot Up
Somehow I missed the notice/discussion about flaky PCM1804 chips. But my high band QMX will sometimes “freak out” with the same noise in the audio recording above, at ear splitting volume. In fact, I don’t use headphones with that radio for fear of more hearing damage.
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But can I replace the PCM1804 for a reliable fix?
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Re: Straight Key Cable Question
THanks for the clear answer. On Mon, Mar 17, 2025 at 6:52?AM resuscitationpicture via <resuscitationpicture= gmail.com@groups.io> wrote:
Always use stereo plugs for straight keys or keying lines. Leave the middle contact unconnected and do not shorten it to ground. Some rigs expecting paddle input will show odd behaviour with mono plugs even in straight key mode. That's just my two penn'orth - the guys at should know what they are doing.
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Re: Successful QMX+ Build!!!
Thanks Bob N4REE,
I guess you just need to be patient when there is a pileup.. since some stations are using max allowable power!
haha
QRP has amazed me lately.. 5w or less and here we are talking to someone across the country.
I thought it was silly at first.. since my 5w HT can’t go far at all… but when you get up into HF frequencies.. 5w has a different meaning!!
72,
Mike
KK7MMN
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Re: QMX+ QMX Build Tips - My 2 Cents
Thanks Jim for the Tips and Tricks!!!
Hacking reminds me of ‘Jim of the Jungle’ and now that tune is in my head!
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I tried the suggested porcupine method on T501 to see how I liked it. ?Works like a champ. I have a working QMX+ and yet it looks like a spider is in there on the PCB.
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The tri-color tip worked well also. Green/Gold/Red makes that toroid look like Christmas!
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Thanks for the tips and encouragement!
Mike
KK7MMN
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Re: QMX Loud Noise on Boot Up
I have that exact same noise as well, maybe about 10% of the time.? In my case I can power off / on again and all is well.? My unit also dates back to the questionable batch of PCM1804 ICs so I have acquired some new ICs from Mouser.? As it stands now I'm just living with the issue since it doesn't happen that often.? If it starts being more bothersome then I will do the replacement.
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QMX+ Receive sensitivity and birdies
Hello everyone,
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I own a factory built QMX+ and was using it yesterday on 30M and suddenly in the middle of transmitting, it seemed like I wasn't hearing receive in between sent elements. Upon further investigation, it seems like overall receive sensitivity decided to just greatly decrease. In addition, I now hear multiple birdies across multiple bands, some quite strong, together with the reduction in receive sensitivity. They are rather pure tones, and there are a lot of them across the bands.
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I reset the firmware, and the problem persists. Whatever is going on, it was something that happened suddenly. SWR was/is fine, and power out is normal. But receive is severely compromised on sensitivity an spurious tones.
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I'm bummed... any suggestions where to start??
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Joel W9JFK?
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Re: Successful QMX+ Build!!!
You will be amazed! I use my home built high band QMX to do POTA hunting with backyard antennas from my HOA residence in Central Florida. With more than 3000 POTA QSOs in the log, everyday coverage for about 3/4 of continental USA is normal and much farther with good conditions. Imagine Alaska, Ontario, Puerto Rico and Germany from Central Florida with 5W and a wire!? Enjoy your QMX+
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72 de N4REE, Bob Easton - QRP CW forever
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Wow,? Switchcraft is 15 doll hairs each? plus shipping! And it IS NOT gold plated.?
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Still searching.? lol
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regards,
Bryan, N0LUF
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Before Joe N2DI's explanation, I was also confused. Yes, the cascading is automatic, depending on the passband and center freqs you select. The part of Joe with a great chart that helps make decisions on which filters are useful with which settings.? After that watching that a couple of times, the actual filter selection works great. Beware... listen to the explanation AND the chart.
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72 de N4REE, Bob Easton - QRP CW forever
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Re: Another Jeff Moore W1NC Repair Rescue
Jeff also skillfully repaired my QMX+, which included replacing the CPU.
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? 73
??? KD8CGH
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Stan has also spent a lot of time helping me as well. He was a great help dialing in my QMX+
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Re: Straight Key Cable Question
Always use stereo plugs for straight keys or keying lines. Leave the middle contact unconnected and do not shorten it to ground. Some rigs expecting paddle input will show odd behaviour with mono plugs even in straight key mode. That's just my two penn'orth - the guys at should know what they are doing.
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Hear here!? While I'm CW only, I find the high band QMX very satisfying. Excellent receive sensitivity, and enough power to reach Alaska and Germany from Florida.? THANKS Hans.
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72 de N4REE, Bob Easton - QRP CW forever
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... AND to freely offering so much good troubleshooting advice. Stan and others like him are a real treasure for this community. Even though my home-built high band QMX is working wonderfully, I come to this group every day to watch how very well the community works. WONDERFULLY!
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[Now, if people would quit asking about >12v.]
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72 de N4REE, Bob Easton - QRP CW forever
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Re: New QMX build, No TX power
On Sun, Mar 16, 2025 at 10:44 PM, Rocky McCleary wrote:
SWR jumps between 1.0 and 3.0 with a dummy load
No wattage in TX in diag page or on LCD
About 100ma draw on TX +-10ma
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This points to a problem with the PA stage, it should take more like 500 mA on Tx.? I'd start by checking the continuity of L502 and T501, especially the primary.? If you have a scope check the Bases and Drains of the BS170s, you should see waveforms at the Tx frequency.
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Also run the terminal tests, especially the Rx ones.? These will help check the LPF and BPF filters.
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With no power the SWR will be inconsistent because it's comparing two very small numbers, the forward and reverse voltages.
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Chris, G5CTH
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Re: QMX Loud Noise on Boot Up
I also have this incredibly loud noise on startup from time to time. I have found that if I just turn the audio volume down it is fine. It's as if the software "forgets" the audio setting sometimes, and sets it to max.
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Sverre
LA3ZA
http://la3za.blogspot.com
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Re: Purchase transport problems
Kevin, my QMX has just returned from the States, where Jeff Moore did an amazing job fixing the many problems it had. I asked him to mail it to my post office parcel locker, which he did. All went well and I received a text from the Post Office saying it is ready for collection. I collected it without issue this morning.
Regards
Grant VK4JAZ
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Re: QMX SSB - 5 watts of magic = 20 watts normal
Your oscilloscope displays the frequency as 50 kHz in both photographs, I assume this frequency measurement is not real
Only Hantek’s knows why a 51 MHz signal is measured 50 kHz !
Those photos were taken from my experience with a homebrew 6 meter class E SDR TRx.
An FT817 with proximity capacitive coupling to a dummy load and related DUT, was monitoring 51 MHz. I had intentionally toggling PTT switch and spinning FT-817 tuning knob to confirm to viewer that mine is a physically real time test (except a latently delay of a poor man Hantek DSO)
I was trying to work out if the display was the RF or just the envelope (at AF).?
Guido’s compression ratio was set to 8 ( 8 levels)
Personally?I think what you have there is a splatter generator :-D? If those are RF waveforms on your 'scope is't just clipped RF and that will produce a quite nasty result if you look at it on a spectrum analyzer. I think even the original github page? acknowledges this, the?intermodulation products are much higher for constant envelope SSB case than varying envelope.? ?
Two tone was set to 1200/1400 per his publication on GitHub.
That was a very misleading set of measurements,?on that github page. I am looking at? where two-tone signals at 1000 and 1200 were mentioned. To quote intermodulation products at narrow tone spacing in a polar modulation SSB exciter is misleading because the intermodulation products are NOT the same at all tone spacings. The intermodulation gets worse as the tone spacing is increased. The "industry standard" two-tone test has become 700?+ 1900 Hz, this much wider tone spacing is considerably more challenging for polar modulators (EER). To make comparisons, the two tones used must be the same as everyone else is using; particularly in this case where the IMD products are so dependent on the spacing between the tones.? My QMX testing has been done at the standard 700?+ 1900 Hz for this reason.??
? How N1RM measures CESSB power output
from? N1RM which described his method of measuring CESSB based on K4 / R29 compression, confirming +4dB at compression level 30.
? Thanks, I had read that before some time ago but it was nice to re-read it now. In QMX I separated CESSB and Compression. This will become clear in the near future when I finish documenting the changes, for the beta release. There's a Mic Gain, then an Equalizer, a Mic AGC, Compressor. All that is done on the microphone signal before it enters the SSB modulator, and all those stages are configurable. CESSB must be applied AFTER the Hilbert transform in the SSB modulation process (by definition, since this is what causes the overshoots).?
? Dear Hans, I believe that you have a better way than Rick? for measuring your CESSB, a justifiable reason to disturb you.
Please forgive my intrusion to QRP-Labs forum.
No intrusion at all OM, your posts have a very high SNR and are very welcome :-)? I think Rick's approach was quite thorough. I had the advantage of being able to play around "under the hood", meddle in the code, which Rick could not do on these "black box" K4's under test.
73 Hans G0UPL
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Re: QMX SSB - 5 watts of magic = 20 watts normal
Your oscilloscope displays the frequency as 50 kHz in both photographs, I assume this frequency measurement is not real
Only Hantek’s knows why a 51 MHz signal is measured 50 kHz !
Those photos were taken from my experience with a homebrew 6 meter class E SDR TRx.
An FT817 with proximity capacitive coupling to a dummy load and related DUT, was monitoring 51 MHz. I had intentionally toggling PTT switch and spinning FT-817 tuning knob to confirm to viewer that mine is a physically real time test (except a latently delay of a poor man Hantek DSO)
Guido’s compression ratio was set to 8 ( 8 levels)
Two tone was set to 1200/1400 per his publication on GitHub.
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How N1RM measures CESSB power output
from? N1RM which described his method of measuring CESSB based on K4 / R29 compression, confirming +4dB at compression level 30.
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Dear Hans, I believe that you have a better way than Rick? for measuring your CESSB, a justifiable reason to disturb you.
Please forgive my intrusion to QRP-Labs forum.
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Pascal Nguyen VK2IHL
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Re: Automatic Antenna Tuner, Internal Battery with a charger and built-in speaker for QMX+. Open Source.
Is it somehow be possible that the ABS remembers the parameters for each band and that the tuner automatically recalls the last parameters if bands are switched either via the radio or wia cat control?
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I think this would be very useful because if you are using digital modes it happens so easily that you switch the band in your software but forget to retune the antenna so my idea was to somehow make the ATU notice when bands are switched. I'm not sure if there are I IO pins or some other way to detect it and then recall the last tuning parameters, or if it is already possible or might we possible in the future or is simply not possible technically.
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I would be very grateful for some info on this topic.
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Mike KK7MMN
N4REE - Bob
Bob Benedict, KD8CGH
Grant