Topband: AM broadcast tower and 160m dxpedition

[Herb Schoenbohm]

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 at contesting.com] On Behalf Of Richard
> Karlquist
> Sent: Tuesday, February 25, 2014 3:38 PM
> To: topband at 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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