[CQ-Contest] A bandpass filter design

[sq7d at onet.pl]

Look at DG0SA website. He offers bpf too.
Matt
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 On Fri,4/28/2017 12:37 PM, Jukka Klemola wrote:

 PI4CC have a very good single stub system.

 https://www.pi4cc.nl/tech-info/stubs/



 PI4CC have most likely believed the people claiming the double stub 

 would be just 6dB better than a single stub.



That would be true if the two stubs were placed at the same point along 

the line, but each stub provides about 30 dB if they are separated by a 

quarter wave at the harmonic frequency.





 PI4CC result is somewhat better than any 2 stub arrangement would be.

 I have an uneasy gut feeling about the presented filters, how they 

 might drift over time.



I don't doubt their ability to design and build good filters, but 

shoving them into a paint can is a really bad idea, because it limits 

air flow around the circuit elements, limiting power handling. At the 

very least, the paint cans should be perforated (that is, lots of small 

holes, high percentage open) so that they allow air flow but provide 

good shielding.



Also, stub placement with respect to the power amp and with respect to 

the antenna matters a LOT, and can be the difference between almost no 

suppression and excellent suppression. That is, a difference as great as 

60 dB! Anyone using stubs for harmonic suppression should study the link 

I posted about stub placement. http://k9yc.com/LocatingStubs.pdf



73, Jim K9YC

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