[CQ-Contest] [YCCC] Vertical arrays on sloping terrain - opinions please

Dick Green dickgreen at verizon.net
Mon Oct 31 14:25:15 EST 2005


That's a pretty steep hill.

K4SQR told me the feedpoints should be at the same elevation. That caused me
to find the flatest part of the hill I could for my 40m 4-sqr. The max
difference in feedpoint elevation is about 3 feet, so I didn't bother to
compensate. I don't think this affected array performance at all. 15-20 feet
difference on 80m would probably translate to 7-10 feet difference on 40m,
which would have been enough to get me thinking about compensating.

I couldn't find anything on the subject in ON4UN's book. You might try
dropping him an e-mail. W8JI is also an expert on phased arrays (and a lot
of other things) so an e-mail to him might provide some useful answers.
Either one of those guys could tell you the science behind the answer. Also
try searching the TowerTalk archives and posting a query. The subject has
come up before, though I don't recall seeing a good answer.

If ON4UN and W8JI don't have a definitive answer for you, my advice is to
build the array without compensating for the slope of the hill. If the array
doesn't perform as expected (easy to tell from gain relative to a
dipole/monopole, F/B and dumped power), you could raise the feedpoint of the
downhill element(s) by using insulated tower sections. For 80m I don't think
you would have to slope the radials up to the feedpoint -- they could be in
a ring around the grounded tower base. Best to ask the experts about this,

73, Dick WC1M 

> -----Original Message-----
> From: Jim Idelson [mailto:k1ir at designet.com] 
> Sent: Monday, October 31, 2005 12:21 PM
> To: TowerTalk Post; CQ-Contest Post; YCCC
> Subject: [YCCC] Vertical arrays on sloping terrain - opinions please
> I am looking at installing an 80m 2-el or 4-sq vertical array 
> on sloping terrain. the terrain slopes down from 
> approximately NW to SE. I believe the ground will be 15 to 20 
> feet higher on the northwest side of the array.
> My plan is to use radials on the ground, not raised radials. 
> Here are the questions.
> 1. What is the impact of sloping terrain? Does it matter much?
> 2.  What's the best practical way to deal with this situation?
> 73,
> Jim Idelson K1IR
> email    k1ir at designet.com
> web    http://www.k1ir.com

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