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Too Much Power #qrp #cw #qmx

 

The QMX mid-bander (60m thru 15m) is one of my primary radios for portable QRP operations for nearly a year now. The “problem” is that it puts out too much power in CW mode. Here are the numbers using a fully charged 12v battery into a 50 Ohm dummy load measured with an external watt meter:
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60m - 6.1W
40m - 5.3W
30m - 5.1W
20m - 5.6W
17m - 4.5W
15m - 6.5W
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QMX Firmware is 1.00.026
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Question; with the amplitude modulation capability that exists to provide SSB, can the CW mode be enhanced with per band configurations that enable trimming the power down to 5.0W for “by-the-book” QRP and to also lessen any risk to the hardware resulting from power levels that exceed 5 watts.
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I can also see a use case for an easily accessible CW power level “knob” for running QRPp without fiddling with the supply voltage.
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72,
Matt
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The approach I used was adding a high current diode in the power line between the battery and the radio to drop the voltage and reduce the power output.
--
Steve KA0SM
 

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Hi Matt - just reduce your input voltage by adding some series diodes, rated at 2A or so.


Regards

Roger

8P6RX

On 09/04/2025 14:44, Matt - W6CSN via groups.io wrote:

The QMX mid-bander (60m thru 15m) is one of my primary radios for portable QRP operations for nearly a year now. The “problem” is that it puts out too much power in CW mode. Here are the numbers using a fully charged 12v battery into a 50 Ohm dummy load measured with an external watt meter:
?
60m - 6.1W
40m - 5.3W
30m - 5.1W
20m - 5.6W
17m - 4.5W
15m - 6.5W
?
QMX Firmware is 1.00.026
?
Question; with the amplitude modulation capability that exists to provide SSB, can the CW mode be enhanced with per band configurations that enable trimming the power down to 5.0W for “by-the-book” QRP and to also lessen any risk to the hardware resulting from power levels that exceed 5 watts.
?
I can also see a use case for an easily accessible CW power level “knob” for running QRPp without fiddling with the supply voltage.
?
72,
Matt
?
?
 

A fully charged 12 V battery is definitely not 12V
 

Battery measures 12v “key up” and sags to 10v - 11v on “key down” depending on band selection.
 

The diode drop technique is adequate for safety with “12v” batteries that are closer to 14v fully charged, but my goal is equalize the power as close to 5W as possible, across all bands when the supply is actually 12v.
 

Matt, be happy with what you have. The levels you report are very typical of the QMX line. No one will EVER tell the difference between 4.5w and 6.1w. The difference is miniscule. And, no one in the QRP community will notice either. Your antenna blowing in the breeze will cause more variance than those power differences. Look for some YouTube videos comparing different power output levels and you'll discover that doubling the QMX output power will, at best, be less than one half an S-unit at a receiver.? What you are trying to do is like counting Cherrios in your cereal bowl.? Instead, continue enjoying these tiny remarkable radios.
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P.S. I just had a POTA contact yesterday between Central FL and San Diego using a backyard vertical and a new QMX+ with 3.98w on 20m.
--
72 de N4REE, Bob Easton - QRP CW forever
https://bob-easton.com/n4ree
 

If you're trying to get the under 5 W bonus in a contest and you know you're running 6 W that's at least an ethical problem.
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I solved the "12 V" LiFePO problem with an adjustable regulator. My QMX was putting out over 5 W even with 12 V in, so I just ramp it down to 11 V now.

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