[amsat-bb] Re: Mobile Coax?
kl7uw at acsalaska.net
Sat May 30 09:15:21 PDT 2009
At 06:48 AM 5/30/2009, Bob Bruninga wrote:
> > Other Car Tips:
> > Convert from RG-58 to LMR-240-UF
> > or RG-213.
>I'd take that with a grain of salt. The length of coax in a car is
>about say 10 feet. The loss of 100 feet of RG-58 is say 5 dB? and
>the loss of fancy stuff might be 3 db? But the diffrence for only a
>10 foot run is only .5 dB versus .3 dB or only 0.2 dB. Nothing at
>all to even consider compared to all the work it will take, and the
>lack of flexibility and trying to run something almost like pipe
>through places where a simple wire (RG-58) fits.
>My lesson was learned 40 years ago when I go my first 100 lb UHF
>mobile rig (tubes) just after highschool. The boat anchor filled
>the entire trunk of my MGB. But the first thing I did when we go
>the lot of them in my club was spend a day replacing the 8" internal
>piece of RG-58 in mine from the Transmitter output over to the
>chassis connector with a 8" run of RG-8. It was hard work getting
>that 8" piece of RG-8 coax inside the radio and routed all around
>the internal chassis.
>The elmer at the time laughed. He said you just wasted a day and
>all that work to save 0.01% of loss. So now your radio works at
>100% where as before it worked at 99.99%. Losing 3 dB of course is
>one thing (50%), but trying to worry about that last 1% when the
>effort is tremendous is just not effective.
>Anyway, just my 2 cents...
Yep. Commercial NMO mount mobile VHF/UHF antennas typically come
with 17-feet of RG-58 and a connector to install when coax is trimmed
for the particular installation. I have way too many 100w mobile
installs in my past ;-) Of course, FM repeater design is for
overkill on signal margins so no one sweats coax loss for mobiles.
The repeater sites may see 100-150 foot hardline runs, though. I
have one 120-ffot tower with 17 antennas and the coax are 1/2 or 7/8
inch Heliax with the longest run 180-feet.
73, Ed - KL7UW
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