RG8X jumpers will run noticeably warm at 1.5KW key down
at 30 MHz. Power loss is still pretty negligible, however, for short
runs (.11dB for a 6' jumper at 28.5 MHz -> 38 watts distributed
across 6 ft of cable at 1500 Watts CW). We have a bunch in
service at W6UE (3 to 6ft) doing 1.5 KW HF duty in our SO2R
contest antenna switching network with no problems. According
to N6BV's TLW program, LMR240 is slightly better than standard
RG8X (.076dB for a 6ft jumper at 28.5 MHz), so I wouldn't be too
concerned using LMR240 for jumpers in 1.5 KW HF service
as long as the VSWR is reasonable (LMR240 jumpers should run
a bit cooler than regular RG8X jumpers I tested at 1.5KW) . For
bad mismatches (like force feeding an 80 meter dipole with
a tuner on 10 meters), it would be worthwhile to have something
a little more rugged (or better yet switch to a low-loss open-wire
feeder). Also for longer runs, I would be inclined to move up from
LMR-240 to LMR-400 ( 3.8dB vs 2dB for a 300' run at 28.5 MHz).
73 de Mike, W4EF.................................
----- Original Message -----
From: "Pat Barthelow" <aa6eg@hotmail.com>
> Jim does a good job with the details...
> and raises a question....
> Some 20 years ago at a Marconi FM broad cast band transmitter sharing the
> site of a local ham repeater, I happened to grab some RG 213 Jumpers in
the
> the front of the transmitter rack panel. They were carrying the (I
> believe) 1KW FM station's output. They were noticeably warm when my palm
> was wrapped around them. In general, when Ultraflex 240, RG-213, or
> whatever, coax is carrying it's maximum average load, conitunous duty, on
a
> flat swr line, Would a person feel the coax to be cool, warm, very warm or
> hot? Any experience?
> 73,
> Pat aa6eg@hotmail.com
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|