On 2013-07-30 19:46, Jim in Waco wb5oxq wrote:
When choosing a height for a beam is 1/4 wave above ground at the
lowest frequency enough? 1/2 wave? I see Force 12 rating the gain on
their beams at 74'1".
Why that height? At 20 meters is 100' a lot better than say 60'? I
am talking about relatively flat terrain. I see Stepp-ir makes a beam
Well, it just so happens that I have recently been comparing my 2
element
SteppIR at 40 feet to my Monstir (equivalent to a 4 element SteppIR on
20 meters) on a 106 foot crankup tower. The towers are 100 feet apart
over flat terrain.
First, the testing details. I cranked down the MonstIR to 40 feet and
verified, using a previously calibrated S meter, that it consistently
had a 2 to 3 dB advantage over the 2 element SteppIR, which is what
the manufacturer claims. This was a test
of received signal strength, not "readability". This results
were similar for both stateside and DX. I didn't notice much selective
fading where only one would fade. Being only 100 feet apart, I wouldn't
expect much of this.
Then I cranked up the MonstIR to 106 feet and started A/B'ing. In
general,
the MonstIR was noticeably better. Often 6 dB and sometimes 10 or even
15 dB, after subtracting the built in difference of 2 or 3 dB in gain.
The biggest difference was over the north pole to the middle
east. Not so much difference to New Zealand. More difference at night,
little difference in the daytime. If there was QSB, it was usually
worse on the lower antenna. I don't remember the lower antenna ever
being better than the higher one. The height advantage was even more
pronounced on 15 meters.
It is good to know that the big tower really was worth the trouble
to put up.
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