----- Original Message ----- From: "Greg Dolkas" [email protected] To: "AMSAT BB" [email protected] 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:
- 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.
- 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.
- 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