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Guide to optimizing bandpass filters on QMX+

 

I ran the sweeps on the bandpass filters of my QMX+ and while some are excellent, some are quite far off.? Is there a guide to filter optimization a la QCX optimization, or a written guide to approach this systematically?? I think I might be able to figure it out using the utility and my scope, but why re-invent the wheel?
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72
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Charles - NK8O
 

There's an excellent (my opinion) YouTube video by Joe, N2DI, on setting the CW filters for the QMX. Since the firmware is essentially the same in this area, I think it might be very helpful in explaining the relationships between your chosen center frequency and the available bandpass choices. watch::
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72 de N4REE, Bob Easton - QRP CW forever
 

Bob, I believe Charles is talking about the physical LC bandbass filters for each set of bands....the toroids and capacitors.
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-Nate
N8BTR
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The process is quite similar to that of the QCX described by Hans here:
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73. Mike KK7ER
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I'm curious; how necessary is it to tune the BP filters on this radio to get good performance?? (For purposes of this discussion, I would define "good performance" as "at least 75% of optimal output on a given band.") Assuming that you wind the toroids in a tight and uniformly spaced manner, should you expect a lot of variation in performance??
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Thanks,
Steve
 

On 12/01/2025 15:46, Steve H via groups.io wrote:
how necessary is it to tune the BP filters on this radio to get good performance?
Steve,

Is it mentioned in the manual?
Just do the scans, if they are something like correct you may just leave them.

The fundamental test is the difference in noise when the antenna is connected on a dead band.
If it increases then it is good enough.

Saying that many do try to improve results but then you get involved in perceived improvements unless you have instruments.

73 Alan G4ZFQ
 

Anyone willing to share an LTSPICE model of the filters or RF section of the QMX+ ? It would be interesting to compare a lab sweep vs a SPICE simulation sweep.

73, Joe W2JEJ


On Sun, Jan 12, 2025 at 11:40?AM Alan G4ZFQ via <alan4alan=[email protected]> wrote:
On 12/01/2025 15:46, Steve H via wrote:
> how necessary is it to tune the BP filters on this radio to get good
> performance?

Steve,

Is it mentioned in the manual?
Just do the scans, if they are something like correct you may just leave
them.

The fundamental test is the difference in noise when the antenna is
connected on a dead band.
If it increases then it is good enough.

Saying that many do try to improve results but then you get involved in
perceived improvements? unless you have instruments.

73 Alan G4ZFQ
 

Steve, with 4 of the QDX/QMX radios across my bench I have never had an issue with tuning the BPF, LPF, etc. I would like to experiment someday with them, but out of the box the filters are quite satisfactory. ?

73
Dick
W4PID

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