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Re: satelite antenna



John
For others that might have similar querries on the TPMs, I am posting this to
the BB for general info:

n3lsk@imap.pitt.edu writes:

> First, is it absolutely necessary to determine the length the radials are
from
>  the driven elements or could I use your values for the distances in the
article?

The values in the article are pretty darn close and were right on the money
from where my research said they would be.  I used a field-strength meter to
determine the position.  Normally, having a parasitic element this close to a
driven element is not desirable (eg., a yagi beam) because it lowers the
feedpoint impedance too much AND it severly narrows the usable bandwidth of
the antenna.  Neither of these are a problem here because the input impedance
is already very high and the sat frequencies are very narrow.  A plus for a
close reflector is good F/B ratio.  I only suggested you "play" with the
distance to get a perfect match on the SWR meter.  SWR was important to me
because I have about 50' of 9913-flex to both antennas and my 70 cm preamp is
about 20' from the antenna (in the attic).  Every dB counts!

>  Second, is the distance that the two square elements are from each other on
>  the top where they pass through the PVC pipe critical? They almost look
like
>  they are touching but I don't think you would want that.

They are touching, but the wire is insulated (#10 house wiring).  I put a drop
of super-glue on the 70 cm version to keep it tightly in place since I didn't
extend the "mast" that far.  Surprisingly, the super-glue has held up for six
months in the Texas sun without failure.  On the 2 meter version, I slotted
the end of the pvc mast with a hack saw and pressed the wires into the slot to
hold them frimly in place.
  
>  That's all for now. Thanks.

Any others?  Just drop me a note.  I'll be happy to answer any questions I
can.  

73, Jerry
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