[amsat-bb] Re: Polarity questions

[Art McBride]

Luc,
You loose 3 dB if you are not circular. Phasing YAGI antennas at 2.4 GHz is
very difficult, YAGI antennas must be identical and have the exact same
phase center. You would be better off to use a 18" dish and a patch feed, or
a helix. I am not sure that AO-51 is circular polarized on 2.4 GHz. 
Art,
KC6UQH
-Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of i8cvs
Sent: Saturday, September 20, 2008 4:54 PM
To: Luc Leblanc; AMSAT-BB
Subject: [amsat-bb] Re: Polarity questions

----- Original Message -----
From: "Luc Leblanc" <lucleblanc6 at videotron.ca>
To: <amsat-bb at amsat.org>
Sent: Saturday, September 20, 2008 11:53 AM
Subject: [amsat-bb] Re: Polarity questions
>
> I will soon have 2 41 elements 2.4ghz beam installed one vertical the
> other horizontal and i will be able to switch between them. On 2.4 AO-
> 51 there is a strong QSB effect is it coming from polarity change? or from
> the satellite thumbling? Could be i will be able to eliminate
> one variable.
>
> Did any one try to feed 2 antennas through a splitter with one vertical
> and the other horizontal? Is this can solved this polatity
> question?
>
> "-"
> Luc Leblanc VE2DWE
> Skype VE2DWE
> www.qsl.net/ve2dwe
> WAC BASIC CW PHONE SATELLITE
>
Hi Luc, VE2DWE

A two port power splitter 1/4 wavelenght electrically long at 2400 MHz with
characteristic impedance of 36 ohm is only 31 mm long and probably due to
the intrusion for the lenght of three N connectors  will not make the
impedance transformation between 25 ohm of both antennas in parallel to
50 ohm of your transmission line.

If you have available a 1/4 wavelenght two port power divider for 435 MHz
you can readily use it as a quik test because 2400 / 5 = 480 MHz wich is not
too much far away from 435 MHz

Since the ratio by 5 is an odd numbar then the impedance transformation
between 25 ohm to 50 ohm can be accomplished with a small increase in
VSWR

If the above test is encouraging then you can cut the above 435 MHz power
divider to resonate exactly at 480 MHz.

To get CP don't forget to make one coax line 1/4 electrical wave longer than
the other one or to shift one antenna 1/4 wave free space behind the other
one with respect to the satellite...........a very difficult affair at these
frequencies.

In my opinion it would be better to use two helix antennas one RHCP and
the other one LHCP switching polarity with only one coax relay.

Have fun

73" de

i8CVS Domenico






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