[UK-CONTEST] Help with filters and SO2R please

[Cooper Stewart]

Hi Jim,
I have started making stubs and was astounded at the difference it made to
the second radio noise levels. I don't use filters. Immediately check out
K1TTT's web site where there are two excellent articles on stubs. One is
http://www.k1ttt.net/technote/k2trstub.html - the K2TR stub plans.
The better the coax the narrower the bandpass of the stub, the less the
losses, and so the less the heat! Put the stub at the output of your antenna
switch box, and that way it's in place no matter what radio does what. I am
coiling mine up on the floor behind the equipment bench.
Stewart
GM4AFF

-----Original Message-----
From: Jim Martin [mailto:MM0BQI at theRSGB.net]
Sent: 24 May 2002 16:28
To: uk-contest at contesting.com
Subject: [UK-CONTEST] Help with filters and SO2R please


I am looking for some basic information.   I have been unable to find
positive answers to these questions on the web or in the ARRL and RSGB
handbooks.  I can tell you lots about the theory and draw nice graphs but I
do not have the practical experience to put it into practice.
My portable contesting set-up is basic SO2R  with MP and IC746 running 100
watts. The MP will be the main rig and will feed horizontal dipoles on
80 -10m.  The 746 will be the mult hunter rig and will use a multiband
vertical on all bands. They will be about 50m apart fed into the shack with
ldf250 and another quality coax, what would you suggest RG214, Westflex or
another(which is better?)
(I think) I want to put tuned stubs on the output of the MP to cut down
interference to the IC746 when I am listening on the other bands.  My
reasoning is that if I am TXing on the 746 I will be logging a mult QSO and
will not be listening to the MP. (?)  The tuned stubs will be connected to
the main coax with a Tee connector ( one side - rig, other - antenna,
middle - switch box)  On the switch box a tuned stub will be selected to
eliminate interference on the 746 listening band.  Some instances need two
stubs to cover two bands.  Can I put another Tee connector on the output of
the switchbox and connect the two stubs there? (or does this screw up the
impedance completely?)
I have calculated the lengths of the stubs, but with all the switching I
will cut a bit longer and prune using the MFJ.  What should I be looking
for?
What do I do with the stubs? Do they lie along the floor, can I coil them
up, if so how tight, should they go in a metal box etc etc ?
I intend to build a band decoder and automate the process of stub selection.
I have found some circuits but would appreciate others and more info.
I am also building a SO2R controller, again I have circuits and have tried
out ideas which work but would benefit from other circuits ideas.
Alternatively, I have $300 dollars left over from my last trip to Libya
which I am sure Dunestar would change into a nice model 600 automatic band
pass filter but it would not be as much fun or as interesting !!!
Thanks for wading through this epistle
Jim

         *****      MM0BQI  HomePage at  www.qsl.net/mm0bqi       *****
   IOTA DXpedition to EU92   7-10 June and 26-29 July. Look out for GB5SI
Member of the GMDX Group - Scotlands DX Association - www.gmdx.org.uk


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