Hi Luc, I am assuming you meant 7/8" Heliax.
45' of Heliax and a short LMR400 jumper will have around 0.6 dB of loss on 70cm so that just adds 0.6 dB to the noise figure of your preamp (i.e. ~1.0 dB to ~1.6 db.) With even a modest gain antenna, you probably will not be able to notice any difference on a satellite downlink. On 2 meters, even less difference. 73, Tony AA2TX --- At 05:04 AM 1/24/2010, Luc Leblanc wrote: >Yes again a returning question "preamp at the tower or near the shack" > >I will have to do soon some maintenance work on my satellite >antennas tower. I planned to use 2 heliax 1/78" 45' individual line. Each >line will be terminated by high quality 2psp coaxial microwave >switch feeding UHF and VHF antennas. I don't know if i can move my VHF and >UHF preamp at the other end near the shack where each line will >enter the house on short LMR 400 run 10 feet max? > >I know the theory says the best place to put a preamp is at the >antenna but with the very low loss on the Heliax coaxial line, is in the >real world there will be any significant degradation in the noise >figures who will be really noticeable? > >Note: If the relays are introducing too much loss i can feed the >antenna directly from them on the 8' run on LMR-400 directly on the female >N type heliax connector. > >P.S. One commercial microwave technician is telling me that i will >be able to see difference only on labs spectrum/signal generator in >short i will be unable to tell any difference due to the short >length of my coaxial line. He told me he's playing with 300 to 600 feets of >lines in his day to day work and 45 feet heliax run are nearly >consider as jumper line in his world... > > >"-" > > >Luc Leblanc VE2DWE >Skype VE2DWE >www.qsl.net/ve2dwe >DSTAR urcall VE2DWE >WAC BASIC CW PHONE SATELLITE > > > >_______________________________________________ >Sent via amsat...@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 _______________________________________________ Sent via amsat...@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
