[TowerTalk] Stacking

[Frank Donovan]

Hi Mike,

I'd expect the interaction between the 3 element 20M monobander
and the log to be severe unless you can space the antennas at
least 30 feet vertically.   Both antennas would be severely degraded.

The 20M monobander would probably have no directivity at all because
of the multiple near- resonant (near 14 MHz) log elements nearby.

The 20M monobander would likewise destroy the directivity of the
log in the vicinity of 14 MHz.

All of this is best answered by modelling the configuration on EZNEC
or another modelling program.

73!
Frank
W3LPL
donovanf at erols.com


----- Original Message -----
From: Michael Harris <mike.harris at horizon.co.fk>
To: Towertalk <towertalk at contesting.com>
Sent: Friday, December 03, 2004 5:37 PM
Subject: [TowerTalk] Stacking


> G'day,
>
> I'm sure there will be some useful opinions on the following:
>
> I currently run a 5 element 18-30MHz log.  The elements are insulated from
> the single boom and fed with transposed aluminium strip feeders.  No
> problem taping the coax feeder to the boom and I choke it with a ferrite
> 1:1 ballun at the feed.  Anyway that really isn't the question.
>
> I'm thinking of installing a 3 el 20M monobander on the tower and was
> wondering what the minimum vertical spacing between the two beams needs to
> be to avoid disastrous effects between the two.
>
> There doesn't seem to be too much on that subject in the literature that I
> have.  Plenty info on stacking identical beams for gain but nothing on
> Christmas tree stacking of dissimilar beams.
>
> Also regarding my previous post about my 30M vertical with two opposed
> gull wing radials.  I'm not on the beach, 50 metres back from the harbour
> so the near field sees turf, 40cm top soil, thereafter clay.  The coax
> from the solenoid coil choke goes straight down into some buried optical
> fibre cable sub-duct and back to the house.  There are some interesting
> comments and solutions to feeder radiation problems in Moxon's book.
>
> Regards,
>
> Mike VP8NO
>
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