Half wave verticals have been very disappointing to me over the years
when I had the tall BC towers in my backyard to play with after midnight
on 160. I have had much better result in hanging 1/2 wave center fed
slopers of of high towers. Radio stations seem to prefer if they have
extermely high towers like KSTP in St. Paul to split them with an
insulated section and feed them as a Franklin design and pick up some
additional gain along the ground. Some designs do not required two
stacked half waves but achieve significant height by folding back the
top and bottom sections with a cage or in fact using a top hat and an
equivalent on the bottom. The proper phasing section is mounted in a
box at the center split and the feedline is inside the tower. Why this
should work any better than a straight 1/2 wave, as it seems to is
available perhaps in those who can model and compare the two. It seems
however that topbanders who expect good results with a bottom fed 1/2
over a traditional 1/4 wave over a good ground, seem to come away
disappointed like myself.
Herb Schoenbohm, KV4FZ
On 3/25/2014 3:56 PM, Charlie Cunningham wrote:
No, I don't believe 240' is too high - especially if the tower has a base
insulator! It would be so close to 1/2 wave on 160, that it could be fed
very well as a 1/2 wave radiator on 160, either via a parallel tuned tank or
a 1/4 wave of perhaps 450 oh ladder line. A 1/2 wave radiator wis an
excellent transmit antenna, and, because of the high feed-point impedance
can be driven against a very modest ground arrangement
Like you, though, I believe they would do well to put up some terminated
loops, or perhaps a Beverage (or 3?) for receive antennas! A 240' vertical
would, I think, be a VERY noisy receive antenna. If they put up a KAZ
terminated loop that only requires one overhead support, they could steer it
around with ropes and weights on the ground. The KAZ is like ON4UN's FO0AAA
160 receive loop.
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Richard
Karlquist
Sent: Tuesday, February 25, 2014 3:38 PM
To: topband@contesting.com
Subject: Re: Topband: AM broadcast tower and 160m dxpedition
Congratulations on your adventure.
In the past, I have seen some of these AM tower efforts
ruined by lousy receive conditions. I suggest you
get an advance team out to the site to check
out the noise level etc. and maybe put up some
temporary beverages, loops, whatever and LISTEN
on them. Use WWV and WWVH on 2.5 MHz as a beacon.
Others can comment on whether 240 feet is too high.
Rick N6RK
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