[TowerTalk] FW: FW: Stubs

Matt km5vi at flukey.cc
Thu Nov 14 01:53:03 EST 2013

>> The purpose of the stubs if for rejection at the 2nd radio for a SO2R

>> I am putting up antennas for each radio and want to have stubs for each
band.  Just not really sure about where to put the stub in the line from the
radio.  I've gotten lots of good info so think I'm good to go.

Hi Tom,

Adding all the info together it sounds like you are planning to use a tuner
at the shack to achieve multi-band capability through your antenna system -
of at least one of them.  Please advise if this is incorrect.  If so, the
stubs would go on the line side of the tuner and you would have to come up
with some plan to switch them in and out - manual or automatically.  If
automatic then there could potentially be some correction to the electrical
length to compensate for the switching circuitry although this could be
negligible - depends on what you come up with. 

Due to the harmonic relationship of the contest bands, individual tuning
stubs will perform multiple functions on different band combinations.   I
mention this here because it has importance to the stub switching logic that
will be needed.  It is much simpler when you are setting a station position
up to operate on a single band.   In your SO2R case either station can be on
any band so the stub switching logic becomes more complex.  Perhaps there
are some SO2R ops here that have already developed something similar and
will post.  There was a good discussion on this forum not too long ago that
provided a lot of useful information on band-pass and notch stubs that I
would recommend reviewing.   I believe there are some multi-multi contest
station websites that also cover the subject very well. 


>> Do I make the stub for the correct length, hooked to the tuner on the
output of the amp, or do I need to subtract the length from the output of
the exciter to the output of the tuner?

The stub's electrical length is from the "T" connection to the end of the
stub so no, you don't add in the direct feedline length to the length of the
stub.  The direct feedline length, or more precisely, the position of the
stub along the feedline may be important depending on what you are trying to
accomplish with the stub - particularly if you are wanting to use the stub
to transform an impedance, in which case the stub would be placed on the
load side (non-resonant side) of the tuner.  If you are wanting to do band
pass or attenuation with the stub then you would want to stub on the line
side (resonant side) of the tuner.  What stub function(s) are you trying to



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