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Re: Feed line help



At 10:44 PM 8/16/00 -0600, you wrote:
>I met a TV mini-dish installer today, and after asking him what kind of feed
>line they use and describing what I wanted to use it for (turned in to a
>long description of amateur satellite operation), he offered to sell me as
>much as I want.
>
>I'm not very well versed in feed lines, so maybe I can get some advice on if
>this will work well to feed 2m, 70cm, and maybe higher freq. satellite
>antennas?
>
>It's RG-6, with a braided center conductor and foam core.  I didn't get that
>great a look at it, but he called it "Flooded" cable (an explanation of what
>that means would be nice too).
>
>I can buy it from him at $0.15/ft, which seems cheap, but I don't know if it
>will work well, what the loss is like, or what the heck "Flooded" cable
>is...
>
>Any help?
>
>Samuel, W7YYY
>
>
>
Hi Sam,

You can buy the "non-flooded" type RG-6 for about $0.09/ft 
if you shop around. RG-6 works very well for receiving
applications especially if you use it behind a preamp. I have
used it myself. The loss is a bit higher than 9913 but
behind a preamp, you will not notice any difference in SNR at
100' at 436MHz. RG-6 is made with a foam dielectric and is
inherently "water proof" unlike 9913.

The "flooded" type is intended for direct burial. It has an
extra-thick, gooey, liquid barrier inside the jacket. 
This is to re-seal the coax and keep water out even if the 
jacket is slightly damaged. This is to insure reliable 
operation as the CATV companies do not want to try to find a 
break in the cable and try to patch it once it it buried!

RF cables intended for direct-burial generally
use a polyethelene jacket instead of PVC. This is because PVC
out-gassing will damage the inner dielectric when the cable is
buried (not a problem when not buried.)

Although flooded cable is generally overkill for most ham 
applications, it is a good idea to use polyethelene jacket cable
if you intend to bury it (although it takes years for out-gassing 
to cause damage.)


73,
Tony


Tony AA2TX@amsat.org
North Andover, MA

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