[amsat-bb] Re: Coaxial line question

Anthony Monteiro aa2tx at comcast.net
Sun Jan 24 08:26:02 PST 2010

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.

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
>DSTAR urcall VE2DWE
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