K1TTT Technical Reference

To: cq-contest@tgv.com (CQ CONTEST)
Subject: Fw: Auto Switching Stubs.
Date: Thu, 18 Apr 96 23:28:26 GMT
From: w2vjn@rosenet.net (George Cutsogeorge)
Reply-To: w2vjn@rosenet.net (George Cutsogeorge)
X-Mailer: Quarterdeck Message Center [1.0]

A number of people asked for more information on automatic stub switching.  The 
system referred to was built for a west coast contester who uses it in his 
single op, two transmitter station.

A short length of RG214 (needs to have good shielding, length not important) 
connects to a tee fitting which is mounted on the input of a six way relay box. 
The antenna line connects to the other side of the tee.  The six outputs of the 
relay box each connect to a stub.  The stubs are defined as follows:

    A = 1/4 wave shorted 80 meter
    B = 1/2 wave open 40 meter
    C = 1/4 wave shorted 40 meter (which is also 3/4 wave shorted 15 meter)
    F = 1/2 wave open 20 meter (which is also 1 wave open 10 meter)
    G = 1/4 wave shorted 20 meter
    J = 1/2 wave open 10 meter

One or two stubs are selected with a band decoder and some simple diode logic 
as follows:

    160 = none
     80 = A, nulls 40,20,15,10
     40 = B & C, nulls 80,20,10
     20 = F & G, nulls 40,15,10
     15 = C, nulls 20,10
     10 = F & J, nulls 40,20,15

All stubs for one system were RG213 and were coiled up together in a NEMA box 
with the six way switch.

Later, more attenuation was required on 40 meters so an additional box was 
added that nulled 80,20 and 10.  It was connected to the original tee with a 
1/8 wave line.  The input of the box has a 1/4 wave shorted 40 meter stub.  
>From there a 3/8 wave line connects to the output which also has a 1/2 wave 
open stub.  A DPDT relay selects this box when the band in use is 40 meters and 
bypasses it on the other bands.  Forty meter performance was:

    Unit          80      20      10

    Original    -28dB   -28dB   -24dB

    W/added     -64dB   -65dB   -41dB

There are many ways to do this type of thing.  Other combinations could null 
the 15 meter harmonic of 40 meters for example, etc.  The relay box was used 
while cutting the stub lengths to include it's effect.  Performance was 
essentially the same as individual stubs.
George Cutsogeorge,  W2VJN
Umpqua, OR.