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
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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
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