Yes. It's a classic tandem match.
72 de va3rr
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Please read this. For DC all is connected to GND.
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Hello, I am hoping I could get some assistance. I am currently building a QMX. I just installed the SWR bridge and I have continuity between all the connections. Is this correct or was it only supposed to have continuity between the wire pairs??
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Jeff Mooe just does good work can you recomend a Bofend mic to use.
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Re: RF Amp using the now cheap GaN-FET's
Allison would be far more qualified than I to judge how well a part will do as an RF amp,
and I haven't looked for low voltage parts that might be used to replace the BS170.
But just looking at the internal capacitances on p9 of the BS170 datasheet
and comparing that with the internal capacitances on p11On for one of these 650v GaN's
it seems the GaN is roughly double that of the BS170 for a Vds between 0 and 50v.
And since we are using two BS170's in parallel, that puts the capacitances roughly equal.
So to my simple mind, it looks like that 650v GaN might be just dropped in.
That GaN is in an 8x8mm package, big enough for a hobbyist to deal with.
?
I had been looking mostly at Innoscience since they have the ridiculously cheap $0.04 parts on JCLPCB.
The GaN I suggest above is the one I bought on Aliexpress last winter at $2 each.
Power dissipation looks much better than most of the other GaN's I've been looking at.
I see that Mouser now stocks the comparable Infineon GS-065-011-1-L for $3.69 at quantity 10, $2.13 each for a reel of 2500:
I'd probably splurge on the Infineon part, but expect we will eventually find suitable parts for much cheaper.
?
My real interest is a 100W class amp and modulator for the QMX.
I'm thinking a push-pull pair of the above 650v GaN on each, a total of 4 devices.
Perhaps use the Infineon NCP51820AMNTWG to drive the gates, $1.53 quantity 10 on Mouser.
It has a pair of high and low side drivers for the half bridge modulator, appropriate for a 650v GaN.
The RF amp will have both parts with source tied to ground, but could still use the same driver.
Seems fast enough.
?
So we're looking at maybe $25 in parts for a 100W class amp, not counting LPF's and DC supply.
Cheap, but not quite the rock bottom price I was thinking about earlier in a previous post,
?
This might work well to feed roughly 100vdc to the modulator:
I'm personally fine with the price, but should be cheaper ways to do it.
?
Jerry, KE7ER
?
?
?
On Tue, May 27, 2025 at 06:29 AM, ajparent1/kb1gmx wrote:
That is something that would be of interest.
?
The parts I've used would, but they are beamlead and extremely
small.? THey would require a board for sure and precision assembly.
?
The part that has seen the inn650xxx would not be suitable?
as we do not need a 600V device.? A smaller part would be a
better match.
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I can recommend Mr. Jeffrey Moore he reparied mine even though? I tried to repair it my self.
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Thank you for clarifying the STM32 uses a 12 bit ADC. I guessed at 24 bits because of the 24 bit sound card capability. That, however, doesn't nullify my thesis. -Chuck Harris, WA3UQV On Tue, 27 May 2025 07:56:22 -0700 "Jerry Gaffke via groups.io" <jgaffke@...> wrote: Chuck,
Yes, on the QMX the microphones are tied directly to the ADC inputs
of the STM32F processor. A preamp may improve things by slightly
increasing the voltage seen by the processor and also by lowering the
impedance of the signal source, you can do this by using a powered
mic with preamp. Or it may not help much, the output of the
recommended mic element is probably a reasonably good match for the
3v max ADC input.
Another possibility is to feed audio from a high quality mic and ADC
to the STM32F from an external computer (an RPi?) through the USB
connection.
The STM32F ADC's are 12 bits which should be plenty, the 24 bit ADC's
are used only for receiving radio signals. Primary issue is that the
STM32F has lots of other stuff going on that injects noise into those
ADC's. Since roughly the same noise is injected into all ADC
channels, the noise is somewhat reduced by subtracting the noise from
the unused internal microphone from the microphone signal on a
different ADC channels.
For better audio, my first act would be to obtain the electret mic
element recommended by Hans and install that into your external mic.
One of those cheap Baofang hand-held mics should be a good start, but
you may need to enlarge the hole in front of the mic element.? Many
in the forum report excellent audio from this the recommended mic
element.? May not be much point in fussing with it much further than
that. /g/QRPLabs/message/141854
Jerry, KE7ER
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Anybody know what those two shiny blobs between R205 and R208 and Q204 and R210 are for? They show up on page 2 of the schematics as JP202 and JP204. Thanks.
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Thanks for the offer, but I don¡¯t have a 3D printer.
Ken
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Jeff certainly does good work!?
?
If you have access to a 3d printer, and don't want to use the pvc supplied in your qrp guys mic kit, I can share the shell that I designed for it.
?
Congrats on getting on the air!?
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Re: QCX+ adjustement and alignment
Hi Pierre. I also recommend watching that video, especially the part where Hans shows you it is not necessary to clean out the holes. The toroid leads can be soldered to the top side of the board and save a lot of board damage potential, especially if you are making several adjustments to the turns counts. Also, the method is good for any?band, but it is different in the number of turns removed or added, depending on the band. In about 58 twenty-meter versions of the QCX that I have worked on, almost without exception I've had to remove one or two turns max from L3 and none from L2 or L1. As Hans mentions, spread the turns on L3 first. If you see an increase in power out, spread them some more. If power out is still increasing when you have spread them as far as they will go, then remove one turn and continue. When you have reached a peak in power output adjusting L3, then squeeze the turns in L2. If power increases, squeeze them some more to reach a peak. Then, finally spread the turns of L1 for maybe a slight improvement.? Since you are already at 3 watts then you probably won't have to remove more than one turn at the most from L3. Lastly, if at any point you see a decrease in power just take the last turns you were squeezing or spreading and adjust them in the other direction. Don't try to squeeze out every possible milliwatt. When you get to 5 watts at 13.8v input, you are at a really good spot. It is always tempting and sometimes possible to get 6-7 watts output but it isn't healthy for the BS-170s and makes almost no noticeable difference on the other end of the path. Good luck ... 73 .. .Ron
Hello Pierre,
?
I suggest viewing the following video before you remove any windings:
?
73
Evan
AC9TU
|
Based on recommendations on here, I sent my dead QMX to Jeff Moore disassembled in a sandwich bag. It is now back home after he found multiple issues with it (factory assembled). All is working as should. I just finished building a qrpguys microphone to use with it and made 3 ssb pota contacts. This without doing any calibration, just the stock configuration. Thanks Jeff for a great repair!!!
Ken/NO4D
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Looks similar to mine
?
| 160 |
5.3 |
| 80 |
5 |
| 60 |
3.5 |
| 40 |
3.8 |
| 30 |
2.5 |
| 20 |
3 |
| 17 |
3.9 |
| 15 |
3.8 |
| 12 |
1.4 |
| 10 |
2.5 |
| 6 |
1.7 |
|
Re: Elecraft T-1 tuner usage
I just set set CW speed to 0 and touch the paddle :-)
?
|
Re: PTT selection in QMX+
A careful, second or possibly third, reading of the manual revealed the following: "A minor difference is the Band Configuration screen, which is NOT available via the LCD menu....?
Sorry for taking up the space with a question that was clearly answered in the manual!
73,
Ken - K4XL
|
Chuck,
?
Yes, on the QMX the microphones are tied directly to the ADC inputs of the STM32F processor.
A preamp may improve things by slightly increasing the voltage seen by the processor and also
by lowering the impedance of the signal source, you can do this by using a powered mic with preamp.
Or it may not help much, the output of the recommended mic element is probably a reasonably good
match for the 3v max ADC input.??
?
Another possibility is to feed audio from a high quality mic and ADC to the STM32F
from an external computer (an RPi?) through the USB connection.
?
The STM32F ADC's are 12 bits which should be plenty, the 24 bit ADC's are used only for receiving radio signals.
Primary issue is that the STM32F has lots of other stuff going on that injects noise into those ADC's.
Since roughly the same noise is injected into all ADC channels, the noise is somewhat reduced by subtracting
the noise from the unused internal microphone from the microphone signal on a different ADC channels.
?
For better audio, my first act would be to obtain the electret mic element recommended by Hans
and install that into your external mic.? One of those cheap Baofang hand-held mics should be a good start,
but you may need to enlarge the hole in front of the mic element.? Many in the forum report excellent audio
from this the recommended mic element.? May not be much point in fussing with it much further than that.
/g/QRPLabs/message/141854
?
Jerry, KE7ER
?
On Tue, May 27, 2025 at 06:58 AM, Chuck Harris wrote:
In most radios, there would be a microphone preamplifier on each
channel, but this was meant to be a software defined radio, and Hans
thought he could trade the microphone preamplifiers, for a simple gain
multiply command. He had a 24 bit ADC after all.
|
Re: Elecraft T-1 tuner usage
I'll try this -thank you!
|
Re: QMX+ receive current; what's typical?
The QMX uses about 1W on receive so ~83mA at 1v, ~111mA at 9v and ~143mA at 7v. 160mA at 9.28v is a smidge high, but perhaps not enough to worry about?
When you run diagnostics, does the duty cycle for the various SMPS look normal?
gl de Russ va3rr
|
Thanks for the great input.
The more complete short story, as I understand it:
Because of early design decisions, the microphones connect directly
to the microprocessor's ADC inputs.
In most radios, there would be a microphone preamplifier on each
channel, but this was meant to be a software defined radio, and Hans
thought he could trade the microphone preamplifiers, for a simple gain
multiply command.? He had a 24 bit ADC after all.
Sans preamplifier, the microphone's signals are likely well within
the first 16 bits of the 24 bit ADC's range.
The problem is a microprocessor's internal analog signals aren't
clean, and the sales guys rarely advertise that fact.? They are long
on telling you that you have a 24 bit ADC, but short on telling you
that the microprocessor has to be idle for you to make use of the
whole 24 bit range.
And, so it is with the QMX's microprocessor.
When Hans actually started trying to use the microphone inputs,
for the SSB part of the QMX project, he discovered a whole forest
of tone spurs that were easily heard in the range of the
microphone... they were also easily heard in the SSB modulation.
These tone spurs were the result of all of the other routines that
had to run continuously for the QMX to work.
What Hans did to save the QMX SSB project was both obvious, and
a genius move.? He simply took the internal microphone channel,
and subtracted it from the external microphone channel, and the
whole forest of tone spurs disappeared into the mud.
With them went our use of the internal microphone... for now.
Hans will likely turn his fix around, and take the spurs found on
the external microphone's ADC channel, and subtract them from the
internal microphone's ADC channel, and the internal microphone
will be back.
Hans is the proverbial one-armed wallpaper hanger.? He works very
fast, but also has a lot of ground to cover.
-Chuck Harris, WA3UQV
On Mon, 26 May 2025 16:17:13 -0700 "Roy Ashkenaz via "
<cqk2rma=[email protected]> wrote:
> 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
>
|
QMX+ receive current; what's typical?
?
My QMX+, a factory 12v build,? draws 160ma at 9.28v, the voltage at which I operate for tx/rx.
for all modes. Transmit current is consistent with my readings.
?
The various PDF manuals I have searched, speak of ~80ma for rx.
?
I am interested to know if mine is a typical, and how it compares to other
build and operating voltages between 9v and 12v
?
TIA,
?????? Pete/wa4hei
|
va3rr
Micah Blackwood
Ken Kirkley
Jason
Ronald Taylor
Braden Glett