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QRP Labs QMX-PLUS-NRV-CW/FT8/USB

 

From Izmir to Cincinnati in nothing flat !
C'mon NEW RIG !
72,
Bill, N4QA/4/QRP Oak Island ( OKI ), North Carolina, U.S.A.
Re: QMX and SOTA equipment organization

 

Thanks for sharing this. Some great ideas.

Mike Krieger


On Fri, Feb 28, 2025 at 2:19?AM Brien - KE7WB via <ke7wb=[email protected]> wrote:
I used my QMX (60-15) on a SOTA activation this week. I use a linked dipole in an inverted vee configuration on a telescoping pole so no need for a tuner. It works well but I found that juggling all the parts and pieces while trying to make contacts on a windy peak was a little clumsy.? So I am experimenting with this setup.? It is a modified/repurposed plastic clipboard.? I have mounted my battery pack, converter, amplified speaker, CW paddle and QMX on the clipboard.? I moved the clipboard clip to the side so it will hold a folded sheet of paper for logging.? The paddle, speaker and QMX snap into 3-D printed brackets.? For now the battery pack and converter are mounted with velcro.? All items are removable for transport.? I will add a 90 degree BNC adaptor for optimum feedline routing.? ?Not pretty but functional.
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Brien - KE7WB
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Re: QMX and SOTA equipment organization

 

Brien,

I'm a fan of using a clipboard. Though the clipboard itself is the bulkiest part of my radio kit! But it makes a convenient surface to hold in my lap, or even standing up. It also makes it easy to set down my whole station if I need to go adjust the antenna or something.

The DG1JAN antenna winder/balun () has convenient holes to hang from the hooks that remain on the bungee cord securing the radio + battery. At one point I had a key mounted with velcro, but the velcro just tore off the top layer of particle board where it was mounted. If I wanted a mechanical key again, I would mount a metal plate where it would reside and use a key that attaches with magnets. In the meantime, I love my VK3IL pressure paddles for field operations.

Someday I'd like to figure out how & where to secure the speaker.

72 de Todd W2TEF
Re: Anyone familar with sweeps that look like this?

 

Two very square waves in quadrature phase, 4/3 ms wavelength, 750 hz frequency.

You're not even going to tell which radio or which hardware test it comes from?

-- rec -- ad5dz --





On Wed, Feb 26, 2025 at 9:01?PM Daniel ZL2DTL via <radiodanzl2dtl=[email protected]> wrote:
--
Daniel ZL2DTL/ZL4YOTA?
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Re: U3S Drop out on Tx

 

Further info:
External power to 7805 equivalent p/s board was mostly from 9V LFP. But it also did it with bench p/s (known good) and 12V LFP. Also tried bench supply directly to U3S and bypassing the 7805 equivalent p/s board. Behavior similar with all of the above.?
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73, Dan? NM3A
Re: U3S Drop out on Tx

 

This is into a dummy load. All RF connections are well shielded with RG-316/SMA connectors or RG-8X/BNC connectors.?
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73, Dan? NM3A
Z-match tuner 28 MHz issue #10m #antennatuner #z-match

 

I have bought a cheap (though not the cheapest available) Z-match manual tuner for my new QMX+. It worked quite well, except I could not match my multi-band dipole on 28 MHz and even 21/24 behaved a bit strange.? Cross-checking with NanoVNA I discovered that the Z-match actually can match my antenna quite well, however the tune LED indication showed the minimum in a seriously different position of the load capacitor. After some investigation I discovered the main culprit - the PCB path connecting the indication LED with the rest of the respective SWR bridge diagonal runs directly below the load variable capacitor. That must have resulted in significant spurious transfer of RF energy from the antenna output into the SWR bridge circuit, which consequently have been balanced out by tuning the matching circuit somewhere off.
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The remedy was simple, but quite ugly (in the make of mine at least). I cut off the PCB path at both ends and soldered both the LED and rectifying diode out of the PCB, then build an airy construction. I also added a 1nF capacitor parallel to the LED to reduce possible RF potentials in the loop created by the necessary long leads of the LED (which has to be placed in the panel of course).
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The attached photos should suffice as an example. After the change, the 21/24 bands tune completely clean and 28 can be safely tuned, however still requires some small additional adjustment in the work mode. The LED shines a bit in the work mode indicating there is still some spurious RF in the circuit. I am willing to live with it, since further fixes would probably make more harm than good to otherwise neat construction.
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I hope this information helps someone. I suspect the PCB layout of these mini Z-match tuners is wide-spread.
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Jiri, OK5WA?
Re: U3S Drop out on Tx

 

Try it into a dummy load to see if it’s RFI
USB noise

 

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I have my QMX+ with me in Tanzania, so I have a compact and easy to set up radio as I travel.? I am having a big problem with USB noise.

  • noise level is high enough to obliterate most signals
  • FT4/FT8 are unusable due to suppression of signals by noise
  • I can't use a USB isolator because my computer takes USB-C inputs only.? A standard cable USB-A cable with a USB-C adapter does not allow the radio to be recognized.
  • This problem is not apparent with my QDX, and very minimally on my KX3.
  • The QMX+ picks up birdies about every one kHz when the USB cable is plugged in and active
  • Laptop is a Dell XPS-13 9315

Are there any solutions for this?? Any bypassing that can be added.? Suggestions??? I'd like to operate FT8 but as soon as I plug in the cable the stations are all masked by noise.? Clearly there is noise being generated in the laptop, but the QMX seems to have absolutely no suppression to deal with it, unlike most of my other radios.

73

Charles
5H3DX
NK8O
VE3ISD
QMX and SOTA equipment organization

 

I used my QMX (60-15) on a SOTA activation this week. I use a linked dipole in an inverted vee configuration on a telescoping pole so no need for a tuner. It works well but I found that juggling all the parts and pieces while trying to make contacts on a windy peak was a little clumsy.? So I am experimenting with this setup.? It is a modified/repurposed plastic clipboard.? I have mounted my battery pack, converter, amplified speaker, CW paddle and QMX on the clipboard.? I moved the clipboard clip to the side so it will hold a folded sheet of paper for logging.? The paddle, speaker and QMX snap into 3-D printed brackets.? For now the battery pack and converter are mounted with velcro.? All items are removable for transport.? I will add a 90 degree BNC adaptor for optimum feedline routing.? ?Not pretty but functional.
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Brien - KE7WB
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U3S Drop out on Tx

 

Just built a U3S with relay board and QLG2. 7805 equivalent in TO220 case for 5V power. Was working perfectly for a few day's testing.?

then tx started cutting out a few seconds to half a minute after Tx. Turned out voltage was dropping to 4.90 (measured at input to main board) and processor was resetting. Current draw at this point was 280 mA. ?Non transmit current 140 mA. Power output with single BS170 was 200 mW. Processor never resets when in non transmit mode.?

I have touched up a number of the power solder joints (altho they looked fine before) with no change in behavior. Turning down the drive to BS170 to where output was only 100 mW allowed completion of transmissions.?

powering with known good 5V p/s directly did not solve the problem.?

Any idea where to go from here?
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73, Dan? NM3A
Re: Does L502 cause excessive voltages on the QMX finals?

 

Evan,
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I had read the LT-Spice docs and used some of the advanced features a few years ago.
Comming at it fresh late yesterday, it was all I could do to edit a schematic and get a transient analysis going.
I had enough head scratching to do without dealing with advanced features.
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You may have noticed that for the 1:1 version of T501 that I was using, I assumed the inductance
of the two primary windings added together should equal the secondary inductance.
Unfortunately, the two primary windings interact on the same core to give a larger total inductance for the primary.
Instead it is the total turns count of the primary windings that is equal to the secondary winding turns count for a 1:1 transformer.
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Here's how I now think of it:
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############
Inductance on a given core is proportional to turns squared.
Lets assume an AL of 1uH per turn for the core, a 16uH secondary, and a 3:2 turns ratio.
Then the number of turns for a 16uH secondary winding is sqrt(16) = 4 turns
? (working back we have: ? 1uH/turn * 4turns**2 = 16uH)
The total number of turns on the primary is 4 * 3/2 = 6 turns
Each half of the primary has 3 turns.The inductance of each half of the primary is: ?1uH/turn * 3**2 = 9uH
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In general the formula for the inductance of one winding of a center tapped primary given a turns ratio of N:1and a secondary inductance of Ls is:
L_one-primary-winding = ( sqrt(Ls) * N / 2) **2?
For the above example:? ? ( sqrt(16) * (3/2) / 2 ) **2 = 9
############
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I've used the above to adjust the transformers in the new simulation schematic QMX_sim04.asc
In addition, I changed the turns ratio of T501 to 1:1 for the "Stock with L502 removed" case.
This increases the output to be slightly more than the stock case, but Vds-max across the BS170's is far less than the stock build.
There may be reasons not to do this, but it is worth investigating since the change in build proceedure would be trivial.
If we use this scheme, then everybody builds the QMX with the simpler 9v version of T501, but 12v builds short across L502.
There should also be a 0.1uF cap to ground at the T501 center tap if L502 gets shorted.
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Here's some figures for peak voltages using QMX_sim04.asc:

Vds? ? ? Output
38.3? ?21.4 ? ? ? ? ? ?Stock QMX, has 3:2 turns ratio on T501
23.8 ? 17.5 ? ? ? ? ? ?With L502 removed, still has 3:2 turns ratio on T501
23.0? ? ?21.6 ? ? ? ? ? ?With L502 removed, now has 1:1 turns ratio on T501
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Note that I am showing 38.3 for Vds-max across the BS170's when simulating a stock QMX at 3.57 Mhz.
Chris reported in a forum post that he measured well over 60 volts using a scope on a stock QMX.
(Unfortunately his graph has been removed.)
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With the 1:1 turns ratio at T501 and with L502 removed, I see a Vds-max of only 23v
and 21.6v across the load. The power into the 50 ohm resistor is? ?(21.6*0.707)**2/50 = 4.66W
My simulation for a stock QMX 12v builds shows slightly less, but real world tests can give over 5W.
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That's all just in simulation, should be interesting to try it on some hardware.
And try it with a whole range of complex impedances at the antenna port, not just a 50 ohm dummy load.
Once we figure out operation at 3.57mhz we might find 4.0mhz significantly different.
And then we only have another dozen bands to figure out.
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It's complicated!
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Jerry, KE7ER
Re: N1MM Logger+'s built-in spectrum display works with QMX I/Q output now

 

I am trying to get the N1MM+ spectrum display working with my QMX+.? I have successfully loaded N1MM+ and modified the function keys to include the KY nomenclature.? The function keys and CAT commands are working properly.
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I downloaded exto_qmx.dll file and copied it from my Download directory to the N1MM+ directory.? When I open N1MM+ and open a spectrum display window I receive the following, "Error opening .\extio_qmx.dll Closing SDR Server".? Also, the lower right corner of the spectrum display is showing the same frequency as the entry window and QMX+.? Please help me understand how I can correct this.
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Howard N8HO
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Re: Higher SWR Dummy Loads ??

 

I put a 50 Ohm dummy load on the antenna side of my ZM-2 tuner, and then connect rig to the transceiver side of the ZM-2.? I can then dial in a range of complex impedances by changing the capacitors and achieve a particular SWR.? Same can be done for a different kind of manual tuner.?
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If you want a resistive-only load to achieve a particular SWR, you can use a resistor across the BNC port.? For example, ~100 Ohms will give an SWR of 2:1, as will ~25 Ohms.? You would likely need to put some resistors in parallel to achieve your desired power rating.? Then you would need to calculate the individual resistor value so that R/n gives you the desired resistance.??
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73
Mike N9OHW
Re: Linux Mint 22.1, WSJTC 2.7.0 and Hamlib

 




Try this Bill!!!
Re: Higher SWR Dummy Loads ??

 

You can read the VNA results at . It looks legit.
This is the finest piece of hillbilly engineering I've seen since the Wouff Hong. :)
Re: U3S- ideas for aux switch #u3s

 

Sorry it took a while to find the manual it has been 4 years sense I built it. ?The screwdriver is pointing at the + feed point fir the LED. I picked up the - from the switch below the LED.
Re: Higher SWR Dummy Loads ??

 

The above was in reply to a suggestion of using a tuner for VSWR testing.
73, Don
Re: Higher SWR Dummy Loads ??

 

Be careful with this, the VSWR you set will likely be wildly different at the harmonics than at the fundamental, and it will cause a different response than a resistive mismatch would, which is the same VSWR at (almost) all frequencies.?
This can be easily checked/verified with a nanoVNA, just set the markers to the fundamental, and to the harmonics which will likely look terrible.? Recall that one of the touted advantages of tuner is harmonic reduction.
The tuner method might for example excite an oscillation which might not occur with a resistive mismatch.
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Another method is to use a short or open after an attenuator, a 3dB pad will yield 3:1VSWR for example.?
You can reverse the phase by swapping open and short, or vary the phase by varying a tank circuit through resonance as a load.? You can get almost 180° phase change in this way.?
We used this at transistor manufacturers for load-pull testing and could get 20:1 VSWR with a low-loss tank at 2 meters.
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I have set up tests at 4:1 using terminations and tees, I could have gone further but I ran out of tees.....
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73, Don N2VGU
Re: Does L502 cause excessive voltages on the QMX finals?

 

Jerry,
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Not sure if you are aware of two features in LTSpice:
1 - You can use Math expressions for the plots.? Here is one comparing the power as V(n003)*I(R1).? You can plot the current through a device.
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2 - you can get the average value with <ctl>left-click on the plot value:
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Unfortunately, you can only get one value at a time.? It is also better to zoom in to a steady state:
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There is a good YouTube series that teaches advanced LTSpice commands:
And the online manuals:
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73
Evan
AC9TU
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