[UK-CONTEST] Help with filters and SO2R please

[Richard Newstead]

Hi Jim

Well the first thing to note is that it can be done - even with a small
station. I used SO2R to win the 21/28 CW restricted section a few years
ago with two dipoles about 6 feet apart (end to end). The filtering may
be tricky and you will probably have to experiment. The Q of stubs is
quite low which makes SO2R on 21/28 MHz tricky. I ended up with just a
single stub on the output of the 21 MHz system as I recall it. It did
take ages to get it working - primarily because the wideband phase noise
of lots of modern radios is poor. Adjusting stubs with an MFJ meter is a
breeze - I think there may be instructions in the MFJ manual about how
to do it. If the SWR on your dipoles is low I do not think that it
should not matter where the stubs are along the co-ax. Use the best
co-ax that you have for the stubs to get the Q up a little. That's a
start.

73

Richard Newstead, G3CWI
Buy and sell  ham gear online at The Amazing Online Flea Market 
http://www.qsl.net/g3cwi


-----Original Message-----
From: uk-contest-admin at contesting.com
[mailto:uk-contest-admin at contesting.com] On Behalf Of Jim Martin
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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