[CQ-Contest] Multiband Antenna separation for Multiplier station...

Mike Smith VE9AA ve9aa at nbnet.nb.ca
Fri Oct 7 15:53:49 EDT 2016

Hi Doug, 


I am sure you'll get more technical answers than mine, but for what it's
worth I run Single OP, Low Power SO2R here with a pair of Icom IC-7410's.

No filters; no stubs.


On the second radio (#2) I only have just a (more or less) Horizontal ZS6BKW
all band dipole (with added 15m dipole attached to it)  which has one end @
50', one end @ 30'. No other antenna attaches to this rig.  The "tip" of one
leg of this multiband dipole more or less points to most of my other
antennas on the other nearest corner of my 2.2ac lot.  I am not entirely
sure this helps, but I'll assume so.


On the main radio (#1) I have any number of different antennas, most of them
verticals or wire arrays and variations thereof.  The closest antenna to the
ZS6BKW is an HF9V vertical with raised radials and it is only about 90'~95'
away.  The farthest is my 80m(vertical) ground plane which is probably more
like 285-295' away.  Most of the other antennas are separated from the
ZS6BKW by roughly 210'.


I don't usually do same-band operation (on purpose) and actually try to
limit harmonic band operation to some degree or operate high in the band on
the lower frequency radio (usually radio #1) to increase my S&P range on the
(other) higher frequency S&P radio (radio #2).  A few weeks ago an apparent
software glitch or something going on with my computer landed both radios on
the exact same frequency a few times over the weekend.  No damage.  Scared
the <beep> out of me however.  I don't know if I would be confident enough
to try that on purpose.


Am I playing with fire?  Maybe.  I made careful measurements with all
antenna combinations using 2 different oscilloscopes before even trying SO2R
at  QRP levels and found as long as I didn't try to listen to 160m on the
ZS6BKW, I could operate safely.


I am really on the brink of if when I operate using radio 1 and radio 2 with
only ~100' separating antennas, however I get 20-30dB of isolation between
the 2 polarizations I am told. (I am not fully confident the feedline on the
ZS6BKW does not radiate a little bit on 80m as I hear a little bit of RFI in
the headphones on 80m..but thankfully 40/80m antennas are 285' apart and I
almost never use the ZS6BKW on 80m and never on 160m.


This is a very long answer to say if I were you I would strive to keep them
200' apart (minimum) and additionally different polarizations to get that
extra 20dB+ isolation!  I did buy the INRAD book by George Cutsogeorge W2VJN
and found it useful, but equally as helpful were the folks here on
CQ-CONTEST and the FB web page by AC0C and also one other ham page that now
escapes me.  All the filters and stubs in the world won't help your
same-band mult hunting.  The only thing that will help you there is
separation and different polarization.  Some of the big Multi-Multis have 4
squares even on the high bands, to get that vertical vs. horizontal thing
working for them.  I believe K3LR is one of them.  W3LPL also (perhaps?)


Thanks for keeping Cuba active in the contests and I hope you did not
receive any damage from "Matthew" this week.


dit dit


Mike VE9AA





We are planning M2 operation for CQWW SSB contest.


We would like install a Multiband antenna for the Multiplier station...to

damage receivers front end, what is the minimum separation between Main 

antennas and a Multiband Mult antenna???


The worse case is trying work a NEW MULT in the same band we are RUNNING. 


Any idea?




Doug, CO8DM

T48K Team


Mike, Coreen & Corey

Keswick Ridge, NB


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