At 02:28 6/24/2005, Tom Osborne wrote:
>I've got the 2nd radio hooked up and going for SO2R operation. I need
>some stubs to cut down the interference between rigs. I'm going to make
>some stubs and was wondering if I could tune them with an MFJ analyzer.
Yup - I do this all the time.
The procedure is pretty basic - but different depending on if you
are making a 1/4 wave or 1/2 wave stub and if it is shorted or
open on the end.
One or two examples probably is the easy way.
To make a stub to keep your 80 meter signal from overloading your
40 meter radio - you will need to put a 1/4 wave (for 80 meters)
open stub on your 40 meter radio input. This stub will be a low
impedance on 80 meters and a high impedance on 40 meters.
You can either tune it on 80 (look for the lowest impedance) or
on 40 (tune for the highest impedance).
To make a stub to keep your 40 meter radio out of the 80 meter
receiver - you will make a stub that is 1/2 wave long on 40
meters (same length as the one above) and then short the end
of it. This one should have a low imedance on 40 meters and
a high impedance on 80 meters.
Obviously - you need to make the stub too long to start with
and prune until you get the null or peak where your target it.
Another trick I use for using 75 Ohm coax on the VHF bands is
to prune the coax so that I get a peak in the impedance with
the other end open. When you do this at the frequency of
operation - whatever impedance you hook up to one end will
show up at the other.
If you are doing this on two meters - you might need to take
care about the effective length of coax between the guts of
the meter and the SO239 connector. W8JI has some notes about
this on his web site I believe.
Tree N6TR
tree@kkn.net
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