On Thu, 05 May 2011 10:38:27 -0700, Jim Lux
wrote:

That doesn't mean that we actually want to use a 50 ohm load in real
life. Maybe I have an amplifier designed to drive a loop antenna with a
resistive 10 ohm impedance.

Interesting. For a community that is so tight-fisted with cash, and
so brag-hearty with power claims, absolutely no one has ever tossed
their hat into the ring that with lower than 50Ohm termination on
their rig (and I'm not talking about 45Ohms) or with a more than 50Ohm
termination on their rig (and this is certainly achievable with a
72Ohm Dipole and 70 Ohm coax) that they have then proclaimed they
substantially exceeded 100W radiated (or lost to heat for that matter)
by the same degree of offset from 50.


Maybe that's because of tradition.. it's not only hams who do that.

Well, that and the rest doesn't respond to the observation that NO ONE
makes a claim of more power from a rig that DOES NOT have a source
resistance of 50 Ohm.

in the professional world, there's a strong tendency to make the
"interfaces" between subsystems 50 ohms, even if overall system
efficiency might be improved by, say, a 25 ohm impedance.

Retail engineering is ruled by a market economy. You have offered a
reductio-ad-absurdum of the native components offering ~10 Ohms
without the cost of intervening transformers. Such an "improved
efficiency" at lower cost option has been available for decades and
has yet to appear as a retail product for the tight-fisted Ham market.
Market logic shows by the force of economy that such a solution is not
viable.

a far cry from your supposition. Off by 1000%?

Just an example.

An incredibly poor one in the context of 100W transmitters when garden
variety examples abound.

I know that modern parts are MUCH lower.

That deliver 97W into 50 Ohms at 30 MHZ with a nominal 12VDC supply? I
smell another poor example.

It might happen that you could hook up a 40 ohm load, or a 20 ohm load,
and it will work just fine, and may even put out more than 100W.

"May" is lazy, "Does" is more authoritative. Any reports of "Does?"

The link from several days ago for the gentleman who measured the output
Z being around 40 ohms would be a "does"..

"Does" with how much more power? When I observe the contents of the
page at that link = NOT ONE WATT MORE!

In fact, if we follow the logic of lowered Rs yielding more power, his
own data flips this! He reports the same 100W available at higher Rs.

However, all that aside, when you observe your comment above, the link
"Does not" offer any support to it. In fact on9cvd explicitly offers:
"This is an ambiguous message"

Which is curious when the manufacturer of the RD70HHF1 power
transistors gives them a "No destroy" rating into a mismatch of 20:1.
Such is the inertia of 1950s design-think with modern components.

Yes, but the design limit might not be the transistor mismatch. It
might be a thermal dissipation limit, or some other component that's the
limiting factor.

Consult the original spec. It is quite specific. The characteristic
of
Load VSWR tolerance: Load VSWR=20:1(All Phase): No destroy
is not a dissipation reference.

73's
Richard Clark, KB7QHC