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RE: Double Helix antenna

What do you think about building the helix reflector from pcb material,
then etch the filter circuits onto the back side, then feed the filters
to the connectors and preamp?

My ultimate goal would be to make a L/U portable dish 3 to 5 feet in
diameter.  The RX and TX modules would reside on the dish, and can
be fed with an 2M/70cm radio.  These are my random thoughts so far.


 > -----Original Message-----
 > From: Charles Suckling [mailto:csuckling@nhlab.demon.co.uk]
 > Sent: Wednesday, May 30, 2001 10:51 AM
 > To: kevinu@flochart.com
 > Cc: amsat-bb@AMSAT.Org
 > Subject: Double Helix antenna
 > Kevin
 > I have built up a coaxial dual helix for 1269/2401MHz.  It looks promising
 > so far, with acceptable VSWRs on each helix for the appropriate frequency.
 > The coupling between the two helices is -15.4dB at 1269 and -26dB
 > at 2401.
 > I cannot easily determine what effects the helices have on the pattern of
 > each other - tests in the dish will be needed to determine whether the
 > patterns have been affected to any significant degree to cause a
 > noticeable
 > degradation in gain.
 > I have also designed a couple of pcb notch filters, and will be building
 > them later today.  Simulated data shows notches of around 50dB for one
 > filter at 1269 (to be inserted ahead of the S-Band converter) and
 > a similar
 > figure for the other at 2401 (to be inserted between the uplink PA and the
 > antenna).
 > Hope to post some pictures and more details of the antenna and filters on
 > the website soon.  I'll let you know when the data has been posted.
 > 73
 > Charlie G3WDG

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