-----Messaggio Originale-----
Da: <K7GCO@aol.com>
A: <towertalk@contesting.com>
Data invio: mercoledì 20 ottobre 1999 7.12
Oggetto: [TowerTalk] Re: Welcome to towertalk
>
> Has anyone ever added a stub to a 2 element quad relector that was
adjusted
> to best F/B with a relay across it that tuned it for maximum gain? Or
> installing a variable capacitor with the tuning shaft extended to the boom
> and a selsyn motor to tune it for gain for F/B? I was planning to try
both
> of these on a 5 band 2 element quad.
If you plan 5 bands and 24 and 28 MHz are in the project, try first to model
what happens with adiacend band
loops in close proximity, a 10meter quad placing the 12 quads concentrically
is a didactical exercise.
Unless you plan 40 or 80 meters or loaded loops, there is not such
difference in gain and F/B when the antenna is tuned for a good compromise
and nothing justify the remote tuning of reflector.
Moreover this tuning action creates a certain amount of mismatch to be
compensated somehow.
> I had a 5 band 2 element quad, same spacing, with the DE's tied
together
> and it destroys the patterns and a great antenna. I put in the computer a
5
> band 2 element quad with tpered spacing and individuatlly driven DE's and
the
> patterns were better than a mono 2 element quad. That's not true with
> multi-band yagi's. Then I came up with a way to improve it even more.
I've
> got a mono 2 element quad with a yagi director in the computer that gives
a
> 90 db null in the rear. Awesome! That's the largest I've ever obtained.
Don't be fooled by an abstract model, in real life things play different.
F/B is reasonably evaluated if a range degrees and bandwidth is considered
and not for a single discrete angle and frequency.
A sharp notch can exist for a stated frequency, a particular azimut and a
certain elevation but average F/B
can be very poor.
73,
Mauri I4JMY
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