Date: Fri, 5 Aug 2016 09:35:17 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Coax Losses on 160 and 75?
Nothing "however" about it, Roger. Of course it's all skin effect, and
copper-coated or clad onto steel has much greater loss than solid or
stranded copper at these frequencies.
BUT - there's a big difference between copper-clad Aluminum and
copper-clad steel. RF resistance of copper-clad Al is NOT significantly
different from solid/stranded copper at any frequencies where we are
likely to use it.
Yes, at HF the most reliable comparative of cable loss below UHF is the
total resistance of their conductors at the frequency of interest. For
solid copper conductors, DC resistance can be compared, because
resistance at RF is a multiple of the DC resistance. For copper-clad Al,
the resistance of a solid copper conductor representative of the DC
resistance of the center. So -- there's nothing wrong with using LMR400
and other cables with Cu-clad Al center on the lower HF bands, except
that they are NO BETTER than a lower cost coax that provides the same RF
resistance. That's why my table in k9yc.com/Coax-Stubs.pdf lists coax
cables in order of their DC resistance, and why the last column in the
table is cost.
73, Jim K9YC
## How are u measuring loss at a given freq ?? Do u use the online
calculators,
like from Times microwave, where u input coax type, length, and freq ? Or do u
just do it the old fashioned way..and install a calibrated wattmeter on each
end of the coax ??
## I like the wattmeter method, then I know it’s the ....real deal. Just
install a 50 ohm dummy load on the
far end..just after the 2nd wattmeter. Then you can test from 160- UHF.
Then you get real results.
This assumes the pair of wattmeters are calibrated for the freqS to be
tested. They dont even have to be
calibrated, they just have to read identical...when both are wired nose to
tail, in series, at the xcvr /amp.
I wire two in series 1st.....then test to ss how close they are across XXX
bands /freqs. Ok, then remove one of em
and install at far end of coax.
## You folks will be in for a rude awakening if you try this stunt.
Jim VE7RF
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