ke3q at msn.com
Fri Dec 3 22:38:05 EST 2004
My guess is you probably want to separate them quite a large distance since
they both cover 14 MHz, probably a distance similar to what you would stack
two identical beams to use them as an array -- say 3/4 wavelength. I'm not
an engineer; that's just my amateur guess. That is, if you want to minimize
the interaction. Then again, you may find that they may "work" considerably
closer together than that, even though they might not quite work as they're
designed to, pattern, front to back, etc. may be affected.
On verticals on the beach (or not)... my recollection of the Force 12 "Team
Vertical" guys, what they said in a Dayton Antenna Forum presentation (about
one of their 6Y, Jamaica, operations), is that they found signals peaked at
1/4 wavelength back from the water's edge, apparently not at the water's
edge or out on a dock or something.
Also, others have told me, empirically (seat of the pants) that they thought
the advantageous salt water effects on vertically-polarized antennas might
be noticed up to a mile inland from the water. I assume they diminish the
farther away you get after that first 1/4 wavelength.
73 - Rich, KE3Q
----- 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
> 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.
> Mike VP8NO
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
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