The weak point may be the antenna, especially if it is a trapped tribander.
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Triplexer
From: jimlux <jimlux@earthlink.net>
Date: Tue, 19 Apr 2016 07:03:55 -0700
Summing three signals, the maximum voltage will be the sum of the peak
voltages. at 1.5kW into 50 ohms, that's about 400V (387 actually). So
three signals might combine at the peaks to 1200V, which is well below the
voltage rating for most 0.405" coax (like RG-213/RG-8/etc)
However, the total power and loss dissipation is what will get you. The
chart shows max power as 3700W for 7MHz and 2600W for 14 MHz. For such low
frequencies, dielectric loss is negligible, so it's all IR loss, and will
go as the square root of frequency (2600 = about 3700/sqrt(2))
what's really going on is that at 3700W for 7MHz, some amount of heat is
being dissipated in each foot/meter of the coax, and that takes it to some
predetermined maximum operating temperature, taking into account some
(unstated) environment (is the coax immersed in water at 20C? fan cooled
at 40C? or what).
You'd need to figure out the loss at each of your three frequencies, sum
all the dissipations, and see if it works out.
I suspect it wouldn't, at least for the 3 transmitters at 1.5kW case.
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