An excellent but short article on the subject of double 1/8 wave coax filters
appears in the Jan/Feb 1998 NCJ magazine.
The parallel combination of one open and one shorted 45 degree stub basically
forms a parallel tuned circuit on the band in operation and attenuates the
second harmonic over 30 db, some 6 to 10 db more than a 1/4 wave stub alone.
In addition to the greater attenuation, the bandwidth of attenuation is also
greater.
A combination of both types reaches almost 40 db attenuation. The article
doesn't mention it but this scheme will also highly attenuate broadcast
station energy due to the low shunt reactance of the shorted stub branch.
It would be interesting to sweep such a device to see how it works at even
higher harmonics where the 1/4 wave stub resonates as 1/2 wave and has little
or no attenuation.
Just an FYI note: 73 de Gerald, K5GW
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