[TowerTalk] Coax STubs for SO2R

[David Robbins]

there can be several reasons for not seeing it on the second receiver. I don't know the aa-230pro, but you should be able to measure a high swr if you try to go through it on 20m or 15m, it should look like a short on those bands.

why it may not cause a difference in the receiver...
1. too strong a signal.  turn tx power to minimum, insert rx attenuator, get the rx signal down below s-9 at the most and try again.  many radios will not be able to show the difference well if the signal is too strong.  also some radios don't handle the out of band overload well and will create the harmonic in the receiver itself.

2. leakage between the radio rf paths... I had bad leakage between two ice 419a filter boxes, rf was coupling to the power and control cables and being conducted between them.  the same could happen with power meters or other things that might be before or after the stub.

3. rectification outside.  if there is something outside rectifying the signal the stub won't have any effect on that.

While stubs are good to reduce harmonics at high power I highly recommend lumped filters between the radio and amp, the rejection is much better than any stubb can be and they can handle all the bands from one box... a full set of stubs for two radios for all bands is a lot of coax to switch around.


Sep 7, 2015 06:36:49 PM, ve9aa at nbnet.nb.ca wrote:

I've seen the K2TR stubs, K1TTT page and have recently bought the FB book by
W2VJN

Today, for a change, I had a little spare time so built 2 stubs, but lets
just concentrate on one.

It was supposed to be for the 40m transmitter. 

I roughed out the length, attached a T and my antenna switch (a la VA2UP
method) (which I'll only use for stubs, trimmed it with my AA-230pro

and when it's inline (parallel to my primary antenna switch) I see no
difference at all on 20m or 15m on my 2nd receiver when the stub is in or
out of line

NONE. Like, not even a titch ESP hopeful. (hi)



I presume this is a type 1 stub (shorted 1/4WL type, x velocity factor)



Thinking I had done something wonky, I made another stub from different
coax..same result.



Anyone been down this road?



Too close to rig?



Interaction from my T and 2nd antenna switch? Gremlins? Wrong method using
the AA-230 pro maybe? I am close to that 23' mark.



de Mike (SO2R hopeful) VE9AA





Mike, Coreen & Corey

Keswick Ridge, NB



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