Re: Filters for portable ops

Paul Smith

Ok John and tnx for the information. I have gathered a ton of stuff to go through now this is interesting. I will post back de Paul N0NBD

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From: <> on behalf of John Kirby <n3aaz_qrp_1@...>
Sent: Friday, September 21, 2018 12:33 PM
Subject: Re: [4SQRP] Filters for portable ops
I read with interest your desire to attenuate adjacent band interference during events such as Field Day. 

For FYI, may I suggest a technique our club use that is almost as effective as seperate band pass filters but much, much less expensive and much easier to assemble and test.

The 'quarter wave stub' as transmission line filter:
Published in (almost all) ARRL Antenna Handbooks for several decades.  Most recent 23rd EDITION, page 24-22,
#24.3.3  PROJECT: A Field Day Stub Assembly....

For each station you will need;

Two 40 meter quarter wave (stub) lengths of coax, cut to length using MFJ-259 or such. Then, SHORT stub1 far end, stub2 far end is  OPEN (no connector), both near ends install a coax connector of choice.

Two ON/OFF toggle switch (Lowes or local hardware store).

One metal box (BUD or local hardware) and
Three chassis mount coax connectors of choice and
One "T"  or  four chassis mounts.

The 'PROJECT' connects (via 'T') between XCVR ANT TUNER and ANT feed line.

       Two ON/OFF toggle switches can be arranged such that;

BAND PASS            BAND NULL (30 dB or better)
1)    ALL                               NONE
2)    80                                  40,20,15,10
3)    40,15                             20,10
4)    20,10                             40,15

72 73 88

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