Re: [amsat-bb] Coax

[K5OE@xxxxxxx]

Steve, Robert,
The decision to put the preamp(s) at the antenna is always the right one.  
Even a mediocre preamp will improve the system noise figure if there is more 
than 1 or 2 dB loss in the feedline.  

Your comments about using less expensive (and higher loss) coax after the 
preamp is sensible, but only for a single-mode station.  If you run only mode 
J (V/U), then you could put even something like RG-8X after the 70 cm preamp 
with an insignificant difference at the receiver.  If you use the same 
antennas to work mode B (U/V), however, then the losses on the cheaper coax 
are unacceptable for the 70 cm uplink.  This same scenario applies to the 2 m 
side as well, only the losses may be slightly more tolerable.  I recommend 
you put up the best coax you can afford and is practical for the 
installation.  

I ran 9913F (Cablexperts) to my antennas, but if I had to do it over again, I 
would run hard-line with only a jumper section of 9913F around the rotor.  I 
was lucky enough to win 25 m of Aircom Plus at the AMSAT convention (thanks 
SSB) and plan to use it for my P3D antenna run.  It's specs are in-between 
hard-line and 9913, but appears to be able to take a standard N connector.  
The connectors for hard-line will cost you about as much as a used car :-))
73,
Jerry, K5OE

  > > I'm just getting started in satellite work. I traded in all my old
>  -> junky radios for a bright shiny new FT-847.  I've got antenna ideas
>  -> and some parts scouted out.  Now for coax.
>  ->
>  -> I understand the need for low loss coax.  There are a number of
>  -> choices: 9913F, LMR400, Aircell and others. Are there good reasons to
>  -> choose one over the other?  Any advice from the old hands to an utter
>  -> newbie?
>  ->
>  -> Robert Rice
>  -> WB5PKN
>  
>  This is a good discussion point. Robert, I went through the same
>  decision process about a year ago when I was putting up my tower and
>  satellite antenna array. I have a 72 foot tower with 2/70 beams on top,
>  along with several antennas. I ran "Buryflex" down the tower (from The
>  Wireman) to my junction/grounding box, then LMR400 underground in
>  conduit over to the edge of the house.
>  
>  The key thing that now makes me reconsider the wisdom of using very low
>  loss feedline is that I also mounted preamps right at the sat. beam
>  antennas for best recieve performance. After using the setup for a year
>  or so, it seems that the preamps make SO much difference, that I don't
>  operate without them. If that is the case, then the low loss aspect of
>  my feedline doesn't matter as much, because all that really matters now
>  is the loss of signal between the antenna and the preamp. The preamp
>  itself has enough output signal that RG213 would have done the job just
>  fine. Get the drift here? I think if I had it all to do over again, I
>  would just buy the best preamps I could find and use average loss
>  feedline. This thinking doesn't apply for antenna setups without
>  preamps.
>  
>  Comments from hams with similar setups would be appreciated.
>  
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