K4SAV wrote:
> You overlooked one other complicating factor, feedline length. The
> length of the feedline on the unused antenna determines if the unused
> antenna looks resonant or not.
No I didn't overlook that. I installed remote relays that disconnected
both halves of the unused inverted vee from the coax.
> Experimental A/B testing of closely mounted antennas with uncontrolled
> parameters of feedline length and source impedance can produce some
> really weird results.
The antenna under test was terminated in 50 ohms at all times.
>> Hi, Rick.
>>
>> Those are interesting comments, so I modeled it up with EZNEC with
>> approximately resonant antennas to see what it looked like. Your
>> message says "inverted vee's" (plural), so I'm making the leap to
>> assume you had all three inverted vee's up at the same time and were
>> able to switch between them. Please correct me if I'm wrong ... and
Yes I did that.
>> None of this data should be taken too literally, of course, but the
>> model implies a lot of parasitic coupling between the three antennas
>> that affects the pattern even when only one of the antennas is being
>> fed. Individually, the signal level at 20 degrees varies by 8 db
An inverted vee with its feed point open circuited has virtually
no parasitic coupling effects (you can easily model this).
>> It would be interesting to see someone hang an inverted vee from a
>> pully and rope and take signal strength readings at different
>> heights. I don't have my tower up yet at this new QTH, but if nobody
>> has done so by the time I get the tower up I'll promise to give it a
>> try.
>>
>> 73,
>> Dave AB7E
Did that too. We put an 80m inverted vee on a 115 ft crank up tower
and A/B'ed it with a ground mounted vertical.
At full height, it was on a par with the vertical for DX. For
locals, it was always better than the vertical, but the difference
was 10 dB more at low heights. At low heights, the vertical beat
the vee by 10 dB on DX. This all agrees with modeling.
For some reason, we don't see this neat relationship on 40 meters.
Hopefully, next spring, the MonstIR will go up on the crank up and
we can see how it works at various heights on 40 meters.
Rick N6RK
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