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40-10 qmx

 

Hi all!
?
I want to build a qmx with at least 40, 20, and 10m bands. This is not currently an official build and I was wondering if it is recommended or indorse by Hans. I know that it is possible and I am willing to give up other bands to have all three. Thanks!
 

Hi Jack
?
I want to build a qmx with at least 40, 20, and 10m bands. This is not currently an official build and I was wondering if it is recommended or indorse by Hans. I know that it is possible and I am willing to give up other bands to have all three. Thanks!

Maybe endorsing it would be taking it a step too far.? But certainly QMX was designed to allow this kind of experimentation; the Band Configuration screen (currently only available on terminal login) lets you set up any combination of bands you like. I think it's important to be realistic about what can be achieved; there are 3 LPFs and 4 BPFs. The BPFs can easily suffer unwanted parasitic resonances. The LPFs can be used with care to cover more than one band if they are adjacent bands. Take care to use a spectrum analyzer to measure the transmitter harmonic performance. I rather doubt that coverage of all bands from 40 to 10m is possible cleanly (means, complying with harmonic level regulations) and repeatably?(means, people can easily built it from a manual without necessarily having to fine-tune filters using a spectrum analyzer to achieve necessary performance).

73 Hans G0UPL
 

I had decent luck with the modifications described here, you need to be a bit careful on the harmonic content and the band config; iirc I had better luck with a slightly different low pass config -- I think my unit had better harmonics with LPF 1 selected for the 12m band because the LPF 2 skewed too high and it worked this way without reworking the LPF:

You absolutely will have to do some tweaking and tuning and analysis with a SA to confirm the harmonic content, but if you have the right?test equipment, spare parts supply of NP0 capacitors and toroids, and a willingness to do rework on a very tight board it is doable for sure.

On Tue, Apr 15, 2025 at 10:48?AM Hans Summers via <hans.summers=[email protected]> wrote:
Hi Jack
?
I want to build a qmx with at least 40, 20, and 10m bands. This is not currently an official build and I was wondering if it is recommended or indorse by Hans. I know that it is possible and I am willing to give up other bands to have all three. Thanks!

Maybe endorsing it would be taking it a step too far.? But certainly QMX was designed to allow this kind of experimentation; the Band Configuration screen (currently only available on terminal login) lets you set up any combination of bands you like. I think it's important to be realistic about what can be achieved; there are 3 LPFs and 4 BPFs. The BPFs can easily suffer unwanted parasitic resonances. The LPFs can be used with care to cover more than one band if they are adjacent bands. Take care to use a spectrum analyzer to measure the transmitter harmonic performance. I rather doubt that coverage of all bands from 40 to 10m is possible cleanly (means, complying with harmonic level regulations) and repeatably?(means, people can easily built it from a manual without necessarily having to fine-tune filters using a spectrum analyzer to achieve necessary performance).

73 Hans G0UPL
 

If you follow the instructions on the AI6XG website, you will see that you will have to modify the band configuration table, as it is a departure from the 3 possible QMX configurations that come with the stock firmware.



I have been thinking about building a 30-10 QMX, but haven't decided if I should start with a mid-band or high-band kit. I'm working on a excel table now...

gl de Russ, va3rr

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