[amsat-bb] Re: CP Antenna questions
domenico.i8cvs at tin.it
Sun Sep 23 20:02:58 PDT 2012
----- Original Message -----
From: "Greg Dolkas" <ko6th.greg at gmail.com>
To: "AMSAT BB" <amsat-bb at amsat.org>
Sent: Monday, September 24, 2012 1:18 AM
Subject: [amsat-bb] CP Antenna questions
> Hi folks,
> I've just obtained a nice, old, but disassembled, KLM 144-150-16C 2m
> circular antenna. I think I have all the pieces (yea!). That, plus a
> tree trimmer, and I should be in great shape for an upgrade.
> The old antenna is a linear (vertical) 8 element beam of unknown pedigree.
> It's been working
> fine, but I couldn't pass this one up.
> Three questions:
> 1. The antenna does not have a polarity switch. The instructions are for
> RHCP ("as used by Oscar-7" to give you an idea of it's age!). Given that
> I don't (yet) have a polarity switcher, is that still the best
Hi Greg, HO6TH
Switching from RHCP to LHCP is the best particularly with LEO satellites.
RHCP was nice with OSCAT-10 and OSCAR-13 because they were spin
stabilized over the Z axis wich is not on the actual LEO sats.
> 2. I have a 2m preamp that I have mounted some 10' away from my current
> antenna, on the mast; I'd like to put it closer. Is it ok to mount the
> preamp on the antenna itself, between the elements? I'm guessing not.
> How about on the cross-arm, a couple of feet from the antenna boom?
10' is only about 3 meters long and if you use a good coax cable with
low losses at 144 -150 MHz the attenuation will be fraction of a dB
and the Noise Figure of the preamplifier will be not deteriorated
or increase significantly.
> 3. The instructions recommend routing the cable out the back of the beam,
> and looping it over to the support mast. But that won't work well as it's
> rotated in elevation (it will get caught on the stuff below). My plan is
> to run the cable forward and then sideways out at the mount point in the
> middle. Will this have a significant effect on the polarization? The
> cross-arm is a wood closet pole, not metal, but I'm thinking that the
> antenna should be mounted in the X orientation instead of +, to lessen the
> effect of the cable shield on the pattern. Good idea, or not?
For the above question read please the following document:
> Greg KO6TH
73" de i8CVS Domenico
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