----- Original Message ----- From: "Greg Dolkas" <ko6th.g...@gmail.com> To: "AMSAT BB" <amsat-bb@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 > polarization? 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: http://www.g6lvb.com/fibermetalboom.htm > > Thanks, > > Greg KO6TH 73" de i8CVS Domenico _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb