[TowerTalk] tuners and power rating

Dan Zimmerman N3OX n3ox at n3ox.net
Sun Nov 28 19:04:22 PST 2010

> you really want to test a tuner, try matching a 5:1 mismatch on 160 and
> then
> run 1500 watts through it.

Don't forget to rotate that 5:1 mismatch around the SWR circle on the Smith

Not all 5:1 SWR possibilities are the same in terms of high power matching.
 Even 250 ohms is way better than 10 ohms (and 250 ohms is better than 50
ohms, generally!)

The ham market doesn't demand real specifications out of the tuner
manufacturers, and they're not likely to volunteer such information.
 There's a huge problem of how to present it in any useful way.

Even if you had safe-impedance charts for each of the HF bands for the
best-case tuning solution, you'd be talking ten pages of charts, and each
would need to have a "voltage limited" curve and a "heating limited" curve.
 The "heating limited" one would have to make serious assumptions about the
time on/time off to really specify things usefully for RTTY, etc, and so
would have to be pretty conservative to avoid complaints.

It's a lot easier to say "1500W" and have most of your users know that's a
joke on TB and be very conservative rather than try to specify everything
and still make some people mad when they can just look in your manual and
see a little tiny funny looking region of usefulness on the 160m band.

For what it's worth, I think it's rare that loads "very near 50 ohms" are
easiest to match on Topband.   I'm guessing it's probably a couple hundred
resistive plus a couple hundred inductive that's the sweet spot for a lot of
CLC tees in terms of survival at high power.


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