Really Cool 3400 MHz Filter

                             by Mike, KL6M

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I built this using a chunk of WR90 waveguide, referring to Paul Wade's (W1GHZ) article in Jan/Feb 1999 QEX.

The exact dimensions I came up with are here:  http://kl6m.com/9cm/3400idf.pdf

The filter can be tuned in a couple ways: It can be peaked on frequency for insertion loss less than a dB, I got it down to 0.7 dB. Or it can be tuned for a wider bandpass as shown in Wide1 and Wide2, where it is optimized to cover 3400 MHz as well as 3456 MHz. The wider bandpass actually attenuates the LO frequency by 50 dB, slightly better than when it is tuned right on 3400.

I will be using this filter in my 3400 MHz transverter currently under construction.   I turned all the elements in a lathe to within a couple thousandths of an inch.   The dimensions were obtained using the DOS software INTFIL.EXE, which is discussed in Paul's article. 

See you on 3400 EME !