[amsat-bb] Re: portable questions

Edward Cole kl7uw at acsalaska.net
Sun Apr 8 23:21:23 PDT 2007


At 06:29 PM 4/8/2007, Steve Attfield wrote:
>I have a few questions for the group about a portale setup I'm orking
>on. I intend to use it for both linear transponder and FM satellites.
>the setup will consist of yagis for V and U mounted on a camera tripod
>with a short run 5-6 feet of coax to the radios. the first thing i'd
>like to know is: is it worth it to put something like lmr 400 ultraflex
>or will rg 213 work well. also would it be benificial to have a preamp
>to mount on the feedpoint of the downlink antenna?
>-Steve VA3SAX

Steve,

Good that you posted the second message.  Running very short coax 
lines probably will be fine with RG-213.  I would switch to LMR-400 
at over 25-feet.  Somewhere between 50 and 75 feet one should upgrade 
to at least 1/2-inch hardline for the Transmitter.  For example I 
have a 170-foot run from my shack to the tower-top of my eme 
array.  Using 150-feet 7/8-inch hardline and remainder LMR-400, I 
still have 1.7 dB loss on 2m getting only 67% of my transmit power to 
the antennas.

As far as preamps, it will depend some on what radio you are 
using.  The newer mobile/base radios probably will work fine without 
a preamp on the Leos.  I do favor using them, though.  For the Heos I 
think you should plan on using preamps on the down link whatever band 
that is in use.

This weekend I had some problems with running my 2m SSB Net and 
thinking I lost my tower-top preamp I switched to the transmit feed 
line to bypass it.  It was an eye opener how much weaker stations 
were.  Typical S9+ signals were down to S3-S5.  Fortunately, I 
discovered I had lifted a control line disabling a coax relay (thus 
disconnecting the preamp input) so I avoided a tower climb.


73,
Ed - KL7UW
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