>Can you tell me the difference between RG142 and RG400
>cable except that one has solid center conductor and the
>other stranded. Their electrical performance seems to
>be the same, and their physical dimensions also seem
>equivalent but I was wondering if the RG400 might be
>more flexible and have a smaller bend radius. That
>might be an advantage when threading through the
>airframe, but it might have other disadvatages! Since
>both cables are fairly pricy, I don't want to buy the
>wrong cable!
>
>Thanks again for you helpful advice,
>
>Will Chorley
>
>PS. Do you sell the fiberglass isulation material for
>fuseable link construction, it doesn't seem to be listed
>on your Web pages?
Why use either of these cables? The good ol' RG-58
has been used with great success for about a half
century. The reason the BIG guys (al la 747, DC-10
etc) use this kind of cable is that their coax runs
can be quite long . . sometimes. In a single engine
a/c the longest run is generally to a VOR antenna
on tail (perhaps 20'). Losses in RG-58 at 110 MHz
are about 1.2 dB per 100' (3db is loss of 1/2
the power). A 10' chunk of RG-58 looses .12 dB
and a 20' chunk is .24 dB . . . not worth
worrying about.
Transponders at 1000 mHz will loose 18-22 dB
per 100 feet or 2.2 dB for 10' and 1.1 dB for
5 foot. Here, it's obviously more critical but
even when you go to a twice diameter, lower
loss coax like RG-8 or RG-214, the looses only
go down by about half.
The modern RG cables like 400 and 142 are still
small diameter cables and have losses comparable
to RG-58. They ARE made from Teflons, et. als.
which increases their resistance to temperature
effects but give the very long history of RG-58
and RG-8 in airplanes, I'd suggest that the time
and effort to upgrade your small airplane's coax
cables isn't going to produce any perceivable
value in return.
Another thing to consider for bigger cables are
connectors. The larger (.35 to .4" diameter) cables
take special connectors. I've seen a number of
installations where a builder used straight
coax connectors on his fat coax than added
right angle adapters at each end for installation.
The losses in the adapters may have increased
his total system losses by as much as he saved
by not using smaller RG-58 with the proper
right angle connectors.
Bottom line is that much is said and recommended
with respect to "modernizing" one's anteanna
feedlines in amateur built airplanes. My recommendation
is to save the time and dollars for things that
will make a difference.
Bob . . .
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