Re: [HCDX] Vertical antennas

["Sam Dellit" <dellits@xxxxxxxxxxxxxxx>]

g'day patrick and the gang

i have been thinking along these lines for the past few months, as well.
have some comments in the K9AY reflector, also on the Topband Reflector
and on that latter reflector Tom Rauch has provided feedback
and i think there is also some earlier material by Tom in the archives

some brief comments from my present state of knowledge

(1) no need for loading coils for receive only applications
rf current levels are low and your losses from the earth mat
resistance will be high anyway, exacerbated by the low input
resistance for any practicable vertical antenna height for a mw dxer,
actually i think Tom resistively loads his vertical receive array to
provide a more stable base input impedance and hence greater
pattern stability

(2) most practicable vertical for mw is probably a single section
30 foot length of aluminium irrigation tube - low cost and effective
alternative a set of telescoping tubes can be extended to the necessary
height
just get a 8 foot length of 4" x 4" treated timber, use a posthole digger
to dig a 4 foot hole and attach the tube to the upper 4 foot. you may
want to sleeve the tube section in contact with the post with pvc electrical
conduit
no guying necessary

(3) alternative vertical is the 8 metre telescoping fibreglass pole with a
wire attached
but more costly - brian dodgson used such a setup on his recent central
australia trip

(4) keep the vertical well away from vertical tree trunks - they are
surprisingly conductive
when in live and growing state and will distort your pattern shape by
parasitic reradiation

(5) in terms of signal levels - depending on ground conductivity - every
foot of wire
vertically will produce a signal equal to about ten feet of horizontal
beverage - so
a 30 foot vertical is about the same as a 300 foot beverage (i am looking at
arrays
of 60 foot verticals, but they will have to be guyed at this height

(6) you can phase two identical verticals to get all the classic two mast DA
patterns
of the mw bc stations - with a null in pretty much any direction - suspect
the mfj phaser
would work fine

(7) independent phasing of 3 or more masts is well nigh impossible for
broadband mw
usage, you will need to look at end fire and broadside arrays with
combinations of just
in phase feeding and 180 degree phase shifted feeds

(8) Tom describes his vertical receiving array as "significantly better than
a beverage"

(9) There is considerable engineering journal literature on the subject of
super directive receive antenna arrays (military has obvious usage), go to
the ieee
website and do a search on that topic and you will get about 20 hits i think
and each
relevant article has a bibliography to extend that list

(10) I haven't seen actual details of Tom's array but if not in topband
archive
he may post it for you on the topband reflector, the 160 m hams tend to be
narrow
band focussed but most of their work can be extended to broadband mw dx to
some
extent

(11) i move onto a 10 acre rural block next week so hope to be able to
compare
notes with you on this subject over the coming months

regards

sam dellit  vk4zss brisbane australia



----- Original Message -----
From: "Patrick Martin" <mwdxer@xxxxxxxxx>
To: <hard-core-dx@xxxxxxxxxxxxx>
Sent: Wednesday, May 30, 2001 1:20 PM
Subject: [HCDX] Vertical antennas


> Has anyone experimented with verticals for receiving? I have built a 40
> foot vertical in the backyard with a series of Ground rods for a Ground
> Plane. It is a very quiet antenna I find with somewhat of a lobe to the
> North. The vertical is a wire up a spruce tree and a 15 foot pole at the
> top. Any thoughts on what I could build for a loading coil?  How about a
> series of verticals for phasing? I wonder how this would compare with
> other antennas?
> 73s,
>
> Patrick Martin
> Seaside  OR
> KAVT Reception Manager
>
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