[CQ-Contest] Coax Stubs for SO2R

[Jukka Klemola]

I will try and answer each question below:

2016-07-18 20:37 GMT+03:00 Rudy Bakalov via CQ-Contest <
cq-contest at contesting.com>:

> If we are learning that stubs cannot be placed randomly,


They can be placed randomly.
Even if the stub is not exactly on the hertz .. if it is within, say 50kHz
of the frequency you want to damp / attenuate, it will provide to your
system.

Being like less than 50 ft of coax, the cost is very reasonable, even if
the contribution is 10dB.

The cost (USD or EUR) per dB is very good if not excellent.



> is there a method of tuning a stub that is placed randomly along the feed
> line?


Yes.

Build a station with more than one radio.
Build a stub to one of the radios. Then try some lengths of coax between
the amp output, coax switch, some panel or where ever you have been
thinking to place the stub.
Then change the coax length a little.

I have made male-female coaxes.
One is about 2 or 3ft, other is about 5ft or so and third is maybe 10ft.
I can test any length from about 2 to about 17ft in a matter of minutes.

It is a very quick and effective method to produce actual measurable
results.



> For example, for an existing installation, there is the existing coax run
> from the shack to the remote antenna switch. It is not practical to change
> the length of the coax run. What can be done in this situation, which I'd
> assume is very common, to squeeze the best performance out of a stub?
>

After the remote antenna switch, you have coaxes to monoband antennas, I
presume?

Change the length from coax switch to antenna i.e. place some cable between
the switch and the stub.
No need to touch the coax from station to switch.

Basically .. try.and.measure before applying full power.
This approach usually avoids the .err -phase that is typical to us hams
when we go to deep experimenting mode.


>
> Rudy N2WQ
>
>
73,
Jukka OH6LI