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R: R: Quadrifilar home brew



  ----- Original Message -----
  From: Edward R. Cole
  To: i8cvs ; AMSAT-BB
  Sent: Wednesday, March 16, 2005 4:35 PM
  Subject: Re: R: [amsat-bb] Quadrifilar home brew


  >The main reason that i have experimented on 2400 MHz Quadrifilar Helix
  >Antennas as per AMSAT Journal May/June 2004 was to find the way to
  >produce a LHCP QFA to be used as a feed in a small dish having a low
  >F/D ratio in the order of 0.3 to 0.35
  >
  >Pulling with you for P3E to verify the results !
  >
  >73" de
  >
  >i8CVS Domenico

  Domenico,

  I have just been studying the septum feed for eme use which is very simple
to build and provides both LHCP and RHCP.  I am giving some thought to
building one for my 85cm offset dish on 2.4 GHz.  Have you looked at this
feed?  W1GHZ did an exhaustive analysis of it in 2002 or 2003.  I will likey
make a plain one first, then add a sliding circular choke ring for comparison.
The basic feed is good for f/d 0.35 dishes.  Either a flared horn or choke is
needed for f/d = 0.6 to 0.7.   At present I am using a 5-1/4 turn helix feed.

  Here is a link to the septum design: http://www.ok1dfc.com/EME/emeweb.htm

  73's Ed - AL7EB
  http://www.qsl.net/al7eb


  Hi Ed, AL7EB

  I have carefully studied the septum feed designed by Zdenek OK1DFC that was
also published in DUBUS magazine 1/2003 by Paul Wade W1GHZ and it seams to be
interesting for EME but many more measurements are needed to state if it is
best or not in comparison to the W2IMU or VE4MA feeds for EME

  My experimentation on Quadrifilar Helix Antennas for 2400 MHz was made to
determine how to wound the loops
  and how to connect them to get LHCP to be used as a feed for a dish in order
to radiate RHCP from it as was requested for AO40 ( and P3E in the near
future).

  Since for satellite use a RHCP and LHCP in band feed is not requested as for
EME than a LHCP QFA antenna is very attractive to illuminate as a feed a small
diameter prime focus dish having F/D in the order of 0.3 to 0.35 because the
QFA do not requires a reflector so that the feed blockage of a QFA for 2400
MHz over a small dish do not affect very much the overall illumination
efficiency.

  Best 73" de

  i8CVS Domenico
----
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