[amsat-bb] Exciting Coax
ko6th.greg at gmail.com
Thu Jan 25 05:20:29 UTC 2018
Yeah, really good question, Rick... I think it's a matter of both
frequency and what cable you're using, i.e. how much loss you're
getting. A Really Long Run of RG-8 may be several hundred feet or so
for HF, but only 100 feet at VHF, and 10 feet at 1.2 ghz. If the loss
is enough to matter, or if you need to spend a lot more money on coax,
then it's a Really Long Run.
A 3db loss, for most applications, is about where you can just detect a
difference. Don't forget to add in a little for the connectors. It's a
classic "half an S-unit" on receive, and the loss of half your power on
transmit. So, 100' of RG-8 type coax may be ok for VHF, but starts
becoming a problem at UHF and above. I.e. it's starting to become a
long run for UHF.
At least, that's how I would sum it up.
> I keep seeing all these remarks referencing a "long run"... What is
> considered a long run above VHF? 50 feet, 100 feet, something in between?
> At what point should we be using 9913/LMR-400 coax or LDF4 hardline?
> Rick KE6LL
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