[UK-CONTEST] 2 Station setup ideas please for CQWW
Dave Lawley
g4buo at compuserve.com
Sun Sep 10 06:07:59 EDT 2006
Hi Jim
The one question that needs answering (sorry if I missed it) is are you
going to do Multi Single or Multi Two? I also echo Darren's point, the
split you suggest doesn't make a great deal of sense.
If you're going to do MS then you can perhaps tolerate a greater degree
of QRM from time to time, whereas for M2 you need effective filtering so
that you can run two bands with essentially no QRM (there will always be
odd spot frequencies where you hear a birdie, and there's a limit to
what can be done about direct harmonics).
If you're MS then as a minimum you get six toroids, six trimmers and a 2
pole 6 way switch and make a set of reject filters, for RX only. If
your rig has a separate receive path (like most Icoms) then you just put
it inline, or with a Kenwood or Yaesu you can either put in a relay
which bypasses it on transmit or put in an override switch.
The problem however, if you don't use bandpass filters, is wideband
noise from the other transmitter. I endorse Andy's comment about older
rigs and it so happans that I have a TS830s for sale from a silent key,
it actually has a much better RX than many more modern rigs - let me
know if you may be interested.
The way we split bands for some of the Cray Valley M8C operations is to
run the tribander on 10 and 20 only, and use a homebrew 2el quad on 15.
Quads are great - easy to make (15m not 20!), as much gain as a 3el
yagi, work well close to ground and lightweight. All you need are eight
8ft garden canes, make up the spiders out of aluminium angle.
With this setup, stubs and Dunestar filters we were able to enter Multi
Two in CQWW SSB last year, with about 30ft horizontal separation between
tribander and quad, with essentially no QRM.
The magic number for coax stubs is 22ft. This assumes you're using RG213
or something similar with 66% velocity factor. Start with a 23ft piece
with a plug on one end. Use an MJF or Autek or similar analyser (I had a
Palstar for a while, it proved utterly useless and I have sent it back).
Starting at about 6MHz tune higher and find the frequency of minimum
impedance, from memory on the Autek it typically shows as about 7ohm.
Note this frequency then do the sums to work out how many inches to snip
off to get it to 7.05MHz. Say this is 4.5 inches, I would snip off 3.5
and then re-measure. When making a set of stubs the shack floor ends up
littered with little lengths of coax!
22ft open will reject 40m and 15m, and pass 20m and 10m so that's what
you put on the line to the tribander. 22ft shorted rejects 20m and 10m
and passes 40m and 15m, so one goes on the quad and a second one goes on
the 40m dipole. You can test the stubs in the shack, the 'pass' stub
should have no effect on received signal and will not affect the SWR.
The 'reject' stub will make the band go almost completely dead - the
effect is very impressive.
Working on the same lines you can make stubs for 40 80 and 160. I always
tape the ends of open stubs with red tape, the ends of closed stubs with
yellow/green tape, and coil up the spare coax and fix with cable ties.
Mark the stubs so you know which are which, and be careful of cheapo
PL259 tee connectors - they can fail suddenly. Hunt out the decent
variety or make your own junctions.
HTH
Dave G4BUO
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