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QMX+ RF PWR Question

 

I finished building and testing the QMX+.Receive sensitity looks good on all bands.

Power out is:
160 - 6.4 W
80 - 5.5 W
60 - 4.7 W
40 - 4.7 W
30 - 5.0 W
20 - 3.4 W
17 - 2.6 W
15 - 4.5 W
12 - 2.7 W
10 - 4.5 W
6 ?- 3.0 W
?
The above measurements are from the terminal Diagnostic test and confirmed with external PWR meter.
My question is this: Since there is 4.5 W on 10 meters, is it normal for lower frequencies to be less, i.e., 20 (3.4) 17 (2.6) 12 (2.7)?
I have reheated all solder joints, adjusted windings to be space as equally spaceed as possible on L403, & L404. ?I recheced the windings on BPF and they are correct. The Filter Sweeps alll look normal.
?
Should I leave it "as is" or make a change to BPF L403 and/or L404 -- other?
?
Thanks for any suggestions!
?
73,
Bill
K4GDR
 

Generally the power on all these rigs falls off with increasing frequency

The filters though need stretching, squeezing, turns adding /removing to optimise the filter curves.? ?That's why the currves are plotted in diagnostics.? ?
I'd take a closer look at the filter curves at the 'mid freq Low output frequencies you identified and see what you see at these frequencies

If the best result is obtained with the LPF turns? /spacings over the whole core and evenly so? (minimum inductance)? you will probably improve things (or at least confirm the result)? by removing a turn and trying again . .? ? Likewise if its best fully bunched up adding a turn may help
 

Note that tx power is affected by the LPFs, not the bandpass filters.? Squeezing and/or spreading the turns of the coils can often have an effect on output power (by moving the cutoff frequency, or adjusting the passband attenuation).


On Fri, Oct 4, 2024, 8:27 AM Bruce Akhurst via <bruce=[email protected]> wrote:
Generally the power on all these rigs falls off with increasing frequency

The filters though need stretching, squeezing, turns adding /removing to optimise the filter curves.? ?That's why the currves are plotted in diagnostics.? ?
I'd take a closer look at the filter curves at the 'mid freq Low output frequencies you identified and see what you see at these frequencies

If the best result is obtained with the LPF turns? /spacings over the whole core and evenly so? (minimum inductance)? you will probably improve things (or at least confirm the result)? by removing a turn and trying again . .? ? Likewise if its best fully bunched up adding a turn may help
 

Hi Bill,
Relax. The tweaking of the coils, will not?
change the output enough to make a difference.?
The results are good.?
73,
George
K3GK
 

On Sat, Oct 5, 2024 at 11:11 AM, Jeff | VA2SS wrote:
External power meter are not necessarily precise at those power level and we don't know if it is well calibrated too.
There are many ways to "come a cropper" when calculating power via scope/load methods, as well.?
In addition, non class-A amplifiers' (like these) performance is highly affected by the load (both phase and magnitude) presented to them, at both the fundamental frequency and several harmonics.?
So the test setup has the potential to introduce a lot of performance variation from the amplifier, as well as directly affecting the measurements by its inaccuracies/uncertainties.
?
I used to maintain an engineering lab for a cell phone power amp manufacturer (approximately the same 3-5W power levels) and even with top-flight (HP/Keysight/Agilent) test gear, getting a dozen "identical" test benches to come even close ( a few tenths of a dB) to measuring the same power, gain and efficiency on the identical "golden" unit was a difficult and time-consuming task.?
I even resorted to buying the 12GHz output attenuators from the same manufacturing lot, measuring their input S11 phase /magnitude (most but not all were closely grouped) and setting the outliers aside for other uses, to minimize that variable.??
?
So do not get your hopes up too much regarding comparing test results against other hams in their own labs and testing different units of random vintages and built and tuned (or not) by different people; there are lots of variables there which are out of your control.
?

“If you compare yourself to others, you may become vain and bitter; for always there will be greater and lesser persons than yourself.” Max Ehrmann, Desiderata: A Poem for a Way of Life

There always will be greater and lesser radios, too.? They are all good.
73, Don N2VGU
?
?
 

Thanks for the advice and insights. ?By tweaking the LPF's, I was able to make a few tenths of a watt "improvement." ?I enjoyed the tinkering and may try winding a new toroid or two to see if it makes a further difference. ?Either way, I'm happy with the results so far. ?The fun of building, testing and "tweaking" was more than worth the price of the kit!
73,
Bill
K4GDR
Jeff | VA2SS
 

Thanks Don for your feedback. I am not an experienced tech and I will keep in mind your comment.

Regards. 73 de Jeff | VA2SS
 

Bill,
?
in the QMX+ all the bands (except 160m and 6m) share LPF in pairs (80/60, 40/30) or triples (20/17/15 and 12/11/10). This means that tweaking an LPF to get half a Watt more on a middle band will disturb the output PWR on the other bands that share the same LPF.
?
I personally playeth the "squeeze-me-and-stretch-me" game for about 10 minutes, saw that it was not worth the effort, and started calling CQ straight away HI. Got an immediate 599 and 20min rag-chew on 20m, which is the band I had tried to squeeze and stretch the longest,? and which is still the one with the lowest PWR of all (2.7-2.8W).
?
Most operators fall off their chair when you tell them you are running 3W (I don't even bother saying 2.8W on air...), and if condx are good they rush off to confirm "UR RST IS 599 REAL 599 REAL" in the following QTC? :)
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Enjoy using your QMX+. It's a fantastic little rig ;)
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72/73 de Enzo M0KTZ

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