On 8/1/12 10:12 PM, K8RI wrote:
> On 8/1/2012 11:36 AM, Paul Christensen wrote:
>>> My Times Wire and Cable catalog shows a power rating of 9kw for 142 and
>>> 11.5 kw for 143 at 10mhz . The ratings are less at 50mhz, 3.5kw and 4.6kw.
>>> I have been using 142 on legal limit chokes for several years. Take a look
>>> at the chokes from Balun Designs and DXE. they use the stuff.
>> Another alternative ro RG-142 is RG-400, a premium grade of the same coax.
For coax, it's not always where the power rating comes from (other than
blindly copying from the original MIL C17 standardM), that is, is it a
"power dissipation" limit (in which case loss vs thermal conductivity vs
environment has a big effect), or is it a "peak RF voltage" limit (the
"voltage rating" on coax is specified and measured at 60 Hz, for instance)
I suspect that most mfrs use a combination of factors in their
calculation.. There's probably a "thermal limit" based on loss... for
times microwave LMR 200, there's this data:
at 300 MHz -> 0.32kW (18.6 dB/100m)
at 100 MHz -> 0.56 kW (10.6 dB/100 m)
at 1000 MHz -> 0.17 kW (34.4 dB/100 m)
so power rating goes down as frequency goes up, but it's not nicely
inverse proportion to loss, or center conductor loss, or whatever.
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