I did actually take the QMX apart after I posted, as much out of curiosity as anything else -- I am building a QMX+, but had not actually looked inside the QMX since I bought it used, already built. It was instructive in general. I didn't see anything obviously bad about the solder joints, but I didn't look too closely at specific components like the 20/30 LPF.?
I did not try different cables or connectors for the simple reason that I don't have any. I have exactly one short jumper right now, about 3', and it's brand new. It's UHF male on both sides, so I'm using an elbow coupler to the radio, of which I also have exactly one (coupler, that is, not radio, qv) at this time. One has not had so much time in this hobby as to have acquired lots of spares, yet.
I do see the same result on the diagnostics connecting the dummy load directly to the coupler, though.
I do have other radios whose performance is known and trustworthy that I can test -- I just didn't have time to fetch them to my makeshift work space last night (I also have neither a shack, nor a proper workshop), but testing the power meter against one of them is on my list. I also do have local people who can help me out if need be.
Michael WD0OM
On Fri, Sep 20, 2024, at 08:17, Greg McCain via groups.io wrote:
Just some quick thoughts on your observations.
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RE: low watts out on 30/20.
They share the LPF pair.
Inspect solder joints, turns on the toroids, capacitors etc.
Fiddle with spreading and squeezing turns on those two as well.
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RE: power output differences
Have you tried different interconnect cables or BNC couplers?
Do you get the same results on the diagnostics with just the dummy load connected to the QMX? Try with both interconnect cables and/or BNC couplers.
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Any chance you have a nearby Ham Buddy that can check the new power meter. Or perhaps you have another radio you know works well?
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Hope it's something simple since the new power meter seems to be showing just about 1/2 of the expected power out?
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