RE: [amsat-bb] Helix Match

[Ib Christoffersen <ilc@xxxxxxxxx>]

Hi Jean-Louis and gang,
The construction with four helical antennas is rather critical in practice.
One of the members of AMSAT-OZ, OZ1AED, has made the construction for both
23 cm and 13 cm.
The 23 cm array performed OK after some adjustments. The "tapered line"
arrangement can be used for adjustment - but one must make sure that all
four lines are equal. He did the mechanics and I made the final adjustments
using a HP Network Analyser.
We never got the 13 cm (2,4 GHz) array to perform good enough. The SWR
was very difficult to get low.
I think that the equations you can find for the impedance of the tapered lines are not
too good. Unfortunately I have not had the time to investigate that in a proper way.
Our Swedish fellow amateurs also have investigated the 4 helix arrangement - again at
2,4 GHz with the same problems - and also the gain was far below the expected value.
My own antennas for 2,4 GHz are two 16 turn helix antennas a la G3RUH combined 
at 50 ohm level. Stacked about 2 wavelength apart vertically. That workes OK.
73 de OZ1MY/Ib

-----Original Message-----
From:	Jean-Louis.RAULT@tcc.thomson-csf.com [SMTP:Jean-Louis.RAULT@tcc.thomson-csf.com]
Sent:	28. januar 2000 09:48
To:	amsat-bb@AMSAT.Org
Subject:	RE: [amsat-bb] Helix Match
Importance:	High

In an Engineer's HandBook, I've seen a description a 4 helix 
antenna sharing a common reflector and common connector.
A common coax connector is installed right in the middle of the
reflector, and a wire runs from this connector to each helix.
Each wire is NOT parallel to the reflector and is supposed 
to convert the wxyz ohms of each helix to a 200 ohms impedance
(200/4 = 50 ohms at the connector level).
This seems to be a very clever theoretical solution.
But what about real world ? So many parameters are interacting :+))

73 de Jean-Louis F6AGR


  
  

 > -----Message d'origine-----
 > De: Richard@g3rwl.demon.co.uk [mailto:Richard@g3rwl.demon.co.uk]
 > Date: jeudi 27 janvier 2000 19:24
 > À: amsat-bb@AMSAT.Org
 > Objet: Re: [amsat-bb] Helix Match
 > 
 > 
 > Joe, Gang,
 > 
 >  joseph v murray writes:
 > 
 > > A question if you have time on your interesting matching of 
 > two helix.
 > > Was the reflector a single or did both helix have separate 
 > reflectors.
 > 
 > Separates. Circles of chicken wire (about half-inch mesh).
 > 
 > I think I see what you're aiming at; sure - a wire, at the 
 > right distance
 > from a common reflector, could be used as a feedline.
 > 
 > 73
 > Richard W L Limebear G3RWL
 > g3rwl@amsat.org
 > FOC # 1188
 > 
 >           So many beautiful girls ..... (sob) so little time
 > ----
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