[amsat-bb] Re: 70cm Yagi and AO-51

Andrew Rich vk4tec at people.net.au
Tue Jan 1 15:02:05 PST 2008

So if I make x2 vertically polarised yagis, and then phase them together, I
would gain roughly 3db.

The trade off is spose is the risk of the wrong sense, -20db or -3db (cp
clash or linear)

Andrew Rich VK4TEC
vk4tec at people.net.au <mailto:vk4tec at people.net.au>

-----Original Message-----
From: OZ1MY [mailto:oz1my at privat.dk]
Sent: Wednesday, 2 January 2008 3:08 AM
To: vk4tec at people.net.au; Amsat-Bb at Amsat. Org
Subject: Re: [amsat-bb] 70cm Yagi and AO-51

Hi again Andrew,
Comments after your text.
73 OZ1MY
----- Original Message -----
From: "Andrew Rich" <vk4tec at people.net.au>
To: "OZ1MY" <oz1my at privat.dk>; "Amsat-Bb at Amsat. Org" <amsat-bb at amsat.org>
Sent: Tuesday, January 01, 2008 4:54 PM
Subject: Re: [amsat-bb] 70cm Yagi and AO-51

> If I have this correct.
> 1. LHCP recieved on a RHCP can knock your signal down by some 20dB

OZ1MY: In theory it will be compleately attenuatet - in practice more like
you say.

> 2. LHCP matched with LHCP will result in a good signal.

OZ1MY: Yes

> So how does a linear antenna equate when receiving a circular signal ?

OZ1MY: In theory you loose 3 dB, which is not very much.

> And the other way around, a circular receiving a linear signal ?

OZ1MY: Same as above.


BUT - all this is theory :-)
For AO-51 the attitude of the satellite and the antennas in combination
are fairly stabel, 435.300 MHz RHCP and 435.150 MHz LHCP.
SO-50 have linear antennas on both up and downlink. In spite of
that there can be a large difference between using RHCP and LHCP
when listening to the downlink. That is one of the resons for at lot of
us to have the possibility to switch between RHCP and LHCP.

Even satellites with RHCP antennas may change polarity if the attitude of
the satellite is not right.

I can send you an article about it if you are interested.

> --------------------------------------------------------------------------
> Andrew Rich VK4TEC

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