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#qdx #80m Are there pictures of the RF Filter Sweep anyplace? #qdx #80m

 

Are there RF Filter Sweep screen shots for 80-20m posted some place?

I just completed building my QDX and it seems to be working, mainly. But I'm puzzled by results I'm getting for the RF Filter Sweeps--

The sweep for 80m shows the center frequency down quite a bit, and the filter peak is way to the right on the page. 60m shows similarly.

40-20m all seem to show the center frequency at least in the filter's pass band, which is what I expected!

The screen shot in the 1.05 operating manual is for 20m though the manual refers to 40m. And there are no screen shots for other bands...

Have I missed something?

Thanks,

Paul
 

On 15/11/2022 02:37, Paul - AI7JR wrote:
Are there RF Filter Sweep screen shots for 80-20m posted some place?
Paul,

The home page shows a 40m scan. Hans posted that with no comment, presumably acceptable.

Many people have included scans in their posts better than that and expressed dissatisfaction. I'm not sure what to aim for, some have fiddled with the coil spacing and capacitors to make the traces look good. Maybe they improve performance, I'm not sure anyone has proof.

73 Alan G4ZFQ
 

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Here are scans off my QDX. I think the 40, 30, and 20m scans are plausible.

I have my doubts about the 80m and 60m scans though--especially the 60m scan!

?Any opinions?

Thanks,
Paul

On 11/15/22 08:49, Alan G4ZFQ wrote:

On 15/11/2022 02:37, Paul - AI7JR wrote:
Are there RF Filter Sweep screen shots for 80-20m posted some place?


Paul,

The home page shows a 40m scan. Hans posted that with no comment, presumably acceptable.

Many people have included scans in their posts better than that and expressed dissatisfaction. I'm not sure what to aim for, some have fiddled with the coil spacing and capacitors to make the traces look good. Maybe they improve performance, I'm not sure anyone has proof.

73 Alan G4ZFQ






 

On 16/11/2022 05:26, Paul - AI7JR wrote:
Here are scans off my QDX. I think the 40, 30, and 20m scans are plausible.
Paul

Looking at the dB scale 80m does not look bad, others have posted similar.

60m was not at first included in the QDX spec.
It was only added when it was pointed out that it worked and the harmonic suppression was adequate.
It uses the 40m BPF and LPF.

I always reckon to try before modifying. At 60m 15dB attenuation may be acceptable. Does noise level increase when a tuned antenna is connected? Does it receive well? If it really worries you then adjustment of the BPF will make 40m look worse.

73 Alan G4ZFQ
 

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Thanks for the opinion, Alan-- I was concerned when the graphs didn't meet my expectations and I couldn't find anything to compare them to.

73

On 11/15/22 23:41, Alan G4ZFQ wrote:

On 16/11/2022 05:26, Paul - AI7JR wrote:
Here are scans off my QDX. I think the 40, 30, and 20m scans are plausible.

Paul

Looking at the dB scale 80m does not look bad, others have posted similar.

60m was not at first included in the QDX spec.
It was only added when it was pointed out that it worked and the harmonic suppression was adequate.
It uses the 40m BPF and LPF.

I always reckon to try before modifying. At 60m 15dB attenuation may be acceptable. Does noise level increase when a tuned? antenna is connected? Does it receive well? If it really worries you then adjustment of the BPF will make 40m look worse.

73 Alan G4ZFQ






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