May I add there is also a 0.1amp current draw when pressing the left encoder. I have it connected to the PC and the QMX never registers as a device.
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Sorry for the late reply on this, I have been busy and had not had a chance to sit down and dive into this. There is 13.8V at PWR_ON. The encoder when depressed does show to have ground. VDD has 1.5 ohms resistance to GND. VCC to GND has high resistance then drops. 12V to GND has 22.5kOhm.?
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Re: 3 cell lipo battery, how to use it anyway
ajparent1/kb1gmx wrote ??? LFP are a better match to common 12V system being closer to the ??? nominal ?13.8V (14.6 full charge, 12V cutoff). ? ? They hold a narrower ??? voltage range in use. That may well be true but I think it prudent to point out that this is the QRPLabs forum and Hans has made it abundantly clear, or at least I think so, that 12Volt means 12Volts and not 13.8, 14.6 or whatever other voltage a fully, or even partially, charged battery may reach. And likewise for 9V. Blowing up the finals in a QMX seems to be a popular activity and exceeding the design voltage, whether that's 9 or 12V, is a great way of doing it. That said I still think that this has been a useful and informative thread and say "thank you" to all who have contributed their knowledge. Regards Keith, G0GNL
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Re: 50 Watt Power Amplifier - Low Power, High Harmonics
#50w
#50wpa
Bill,
?
I am not an expert like Evan, but allow me to share some experiment results with you.
?
T3 Output Waveform:
I tried to reproduce the waveform that you observed on my breadboard test set up. It is this kit amp with its QSK circuitry removed, T1-T3 cores changed to #61 material, and 10m band LPF on board. When I input 10m QCX+ signal, I obtained the waveform like the one in the NA5Y¡¯s video. When I changed QCX+ to 15m band, waveform like yours appeared. Please see Fig1 ¨C Fig 3 in the attached file. (Please excuse the horrible photos. The USB connection of my O¡¯scope is not working).
?
Then I built the 80m band LPF as specified in the 50W Amp kit manual, using the cores and capacitors that I had received for this kit, and compared the waveform with those with (1) No LPF and (2) 80m band LPF that I had built per QRPLabs LPF Kit manual (upgraded components to 50W). As you see from Fig 4 ¨C Fig 7, I observed the same waveform as yours with the LPF built per amp kit manual, but not without any LPF nor with the LPF built per LPF kit manual. (many ripples due probably to inadequate grounding, long cabling, poor shielding, etc)
?
From these, it appears the waveform your are concerned with is a typical response of this kit and does not indicate any failure or assembly error. FYI, with this LPF, the power output measures 11.5W at 11V supply, rising to 46W at 20.3V, which is compatible with all the kit amps that I have built.
?
Gate voltage:
Yes, I have been seeing gate voltage to become very high on lower bands. My experiment records also show about 40Vpp on 80m. I believe it would be about the same with all my 6 amps. Good news is that the IRF510s have been working faithfully, even under very high duty cycle usage during 80m/160m band contests, for a few years now without any failure.
?
Your 9.3W at 13.8V supply is a bit low, but not very low. Compared to the 15W at 13.8V value in the manual, the difference is 2dB or one third of an S unit. The difference may be due to variation in components and transformer/LPF windings, and not due to some problem.
?
73, Aki, JO4MTH
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Re: Introducing QMX CARROT
Someone else with similar goals. An ultraportable antenna that can be directly attached to a QMX.
?
https://www.youtube.com/watch?v=xbC59sygb1Q&t=24s
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Sounds like the U.S. penny might be going away.?? I was inspired by the touch feature of DL1CR's touch feature on his QMX Carrot.? This is pretty easy to print without supports, but you do need a couple of pennies!?
?
https://www.thingiverse.com/thing:7049323
?
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Re: Elecraft T-1 tuner usage
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QMX test on SSB from a SOTA summit
Hi All,
?
I activated a SOTA summit yesterday with the QMX to test it's SSB capability. I only operated on 40m, with the expectation that local stations would hear me well and many I've worked before could comment on my audio. It went very well and reports on my signal quality were very good.
?
To my surprise and delight I was called by F5PYI and we managed to complete a contact! Larry was actually not bad copy but constant static crashes from an approaching storm made it hard to hear his call - this was with 5W of SSB on 40m in the middle of the local afternoon. There's a more complete writeup with photos on the SOTA Reflector.
?
?
73? David VK3KR
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What's the short story on why the onboard QMX+ microphone doesn't work (yet).
?
Is there an upcoming solution?
?
Just curious,
Roy de K2RMA
|
It was said, by one with whom I agree: "Does not seem that showing the rx level on the radio primary screen should depend on whether there is an AGC function. Irregardless though, wonder why AGC does is not implemented for digi mode. My other two radios have it and it's definitely useful.' When I asked a similar question, the answers were of the type, "Use the volume control." and, " It means nothing to me." (See /g/QRPLabs/message/145846) I hope you fare better than I. wa4hei
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Re: QMX died before i got a chance to transmit.
Teddy,
?
please read this page from the QRP Labs Wiki. ?
73 Ludwig
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Re: RF Amp using the now cheap GaN-FET's
Allison,
?
Some of them wall warts are pretty good at radiating RF.
That being said, creating a clean signal at 30mhz is a significantly different job
than designing a 500khz SMPS.? As you well know.
?
A few months ago I posted about my dual SMPS board that plugs into the QMX JP105
to replace the on-board firmware driven switchers.?
That board is doing fine, and I am convinced it is a significant improvement
over a stock QMX in a number of ways.
In the Readme, I noted that I tried using one of those switchers as a modulator,
but response was way too slow to properly follow audio even though it was
switching at 2mhz.? I doubt it's possible to use a typical SMPS IC as a modulator.
?
A half bridge class D audio amp looks a lot like a buck mode switcher,?
but is designed to be quick enough to follow incoming audio.
One trick the audio amp has is that it allows reverse coil current,
whereas an SMPS switcher typically does not.? When actively reducing
the output voltage by discharging the output cap with that reverse
coil current, our buck mode switcher topology suddenly becomes a
boost mode switcher pumping power from the SMPS output cap back
to the input supply of that SMPS.? I suspect our modulator will need this trick.
Here's an older discussion:
?
Also, unlike the modulator for an AM transmitter that has a sine wave output when transmitting
a 1khz tone, our modulator for polar SSB will have an output waveform that looks like a
full wave rectified sine wave.? So it will have to make some transitions that are
considerably faster than that AM transmitter modulator.
?
Jerry, KE7ER
?
On Mon, May 26, 2025 at 02:26 PM, ajparent1/kb1gmx wrote:
Jerry,
?
What is the difference between a modern wall wart and a
class D TX?? No rectifiers, filter is LPF suitable for the band
and antenna matching. Oh and stable? frequency source.
?
The hard core class E (and D) guys started over a decade ago using
mosfets (many) in parallel to get to those kinds of power levels,
no valves.?
?
The latest QEX has a 5W wspr tx for 160 to 6.? ?Look at that and the
final the lowly IRF510.? Modulate the DC and its AM.
?
For those high power guys the high voltages might be 120V DC.?
The real trick is enough audio power to modulate the DC to the
levels needed.? No Heising or other mod iron used.? Think SMPS
that can be modulated at audio rate to say near zero to 200V at 10A.
?
Compared to the tubes and all, did time keeping a 3KW AM BCST
station going,? a fork lift was how it was done.? The transformer
for the heater was over 100 pounds for the 3KW TX.? Not
going there!
?
A local station converted the 1KW TX to latest switch mode
tech the 6ft rack in the shed became a 27inch tall by 18 inch
deep and 21inch wide? box with the entire TX in it and powered
off a 220V line (at less than 15A).? ?Smaller lighter and over
all better.
?
--
Allison
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Re: WSPR without GPS unit
I had a similar problem but the screens said "WSPR Power" rather than "WSPR Call". Over and over again I re-entered my call sign, getting no change. Then I realized that "WSPR Power" needed to be taken literally. I had entered "35" for the power despite the fact that the instructions clearly said, "WSPR powers are constrained to certain values 0, 3, 7, 10, 13, 17, 20, 23, 27, 30, 33, 37, 40, 43,
47, 50, 53, 57 and 60dBm."
?
I changed the number to "33" and all is well.
?
When all else fails... read the instructions carefully and literally.
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Re: Solder pot for toroid leads
? Roy,
This is very similar to the one I built from an old modified Radio Shack 110 v heated solder sucker years ago. ?It works. Here's the pictures.
toggle quoted message
Show quoted text
On May 24, 2025, at 2:27?PM, Roy Ashkenaz via groups.io <cqk2rma@...> wrote:
? 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.
?
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.
?
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.
?
Time will tell if I actually use my small soldering pot or the scrap/blob method.
?
Thanks for everyone's help.
?
Roy de K2RMA
|
Re: RF Amp using the now cheap GaN-FET's
Jerry,
?
What is the difference between a modern wall wart and a
class D TX?? No rectifiers, filter is LPF suitable for the band
and antenna matching. Oh and stable? frequency source.
?
The hard core class E (and D) guys started over a decade ago using
mosfets (many) in parallel to get to those kinds of power levels,
no valves.?
?
The latest QEX has a 5W wspr tx for 160 to 6.? ?Look at that and the
final the lowly IRF510.? Modulate the DC and its AM.
?
For those high power guys the high voltages might be 120V DC.?
The real trick is enough audio power to modulate the DC to the
levels needed.? No Heising or other mod iron used.? Think SMPS
that can be modulated at audio rate to say near zero to 200V at 10A.
?
Compared to the tubes and all, did time keeping a 3KW AM BCST
station going,? a fork lift was how it was done.? The transformer
for the heater was over 100 pounds for the 3KW TX.? Not
going there!
?
A local station converted the 1KW TX to latest switch mode
tech the 6ft rack in the shed became a 27inch tall by 18 inch
deep and 21inch wide? box with the entire TX in it and powered
off a 220V line (at less than 15A).? ?Smaller lighter and over
all better.
?
--
Allison
------------------
Post online only,?
direct email will go to the bit bucket.
|
Re: Introducing QMX CARROT
Now the QMX Carrot has successfully completed its second SOTA/POTA activation. And my KX2, remaining in the backpack, is getting jealous.
?
But I almost missed a Summit to Summit due to SWR protection, because the frequency during tuning wasn't the same as the set frequency.
Then I learned that I can, and possibly must, change the frequency in SWR tune to the qso frequency.?
?
73 Chris
|
Re: RF Amp using the now cheap GaN-FET's
No I rarely do am.? ?I did build a retro-75 (SWL circa 2010)
that was class E.
?
While trying to may the uSDR work I found the TX made a fair
AM tx (modulate the DC to the finals).
?
The large size stuff described was written up in QEX years ago.
And the AMwindow likely has posting on that as well.
?
--
Allison
------------------
Post online only,?
direct email will go to the bit bucket.
|
?
The Whitsunday Weekend is the Region 1 CW field day. Get your QRP Labs rig out into the field and have fun. My QMX plus will be there as DL0EU/P
Solar panel power
?
lok for me east of Hamburg
--
Martin
DK3UW
|
you are in my log your Nr. 557? Roelof.
?
I had no rate of 40 but some over 30 but the high bands were painful. I ended up with 700 QSO's. Mixed QMX and Flex 1500. QSK is perfect on the QMX+ and Latency on the Flex is terrible. good, that the sidetome comes from the Winkeyer.? Unfortunately there is no really good QRP Rig available. I would love something with more buttons avoiding all these menue functions.? KX3? ?
?
My antenna is a 160 m loop with ladder line and Johnson Viking Matchbox So band change takes time.
--
Martin
DK3UW
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ZeusK8CES
Roy Ashkenaz
Mike Perry, WA4MP
David Wilcox K8WPE
Chris