In article ,
Sal M. Onella wrote:

My guess(tm) is that most modern HF radios can also safely operate
into high VSWR loads, but suspect that manufacturers are also hesitant
to guarantee such operation. Most manufacturers don't even specify a
maximum VSWR and simply reduce power if excessive reverse power
(usually 2:1 at full power) is detected.

That sounds right..

I have two HF radios, (Kenwood TS-120, TS-870) and I often observe the
forward power climbing as I manually tune and reduce the reflected power.
At first glance, this would seem to indicate the rig had previously
throttled back its output in response to the consequences of a mismatch.

I never intentionally tune at anything more than a few watts, so perhaps the
protection circuits operate at less than full power, too. The autotuner in
the TS-870 uses about 10 watts.

My own experience with a TS-2000 strongly suggests that this radio
does reduce its transmit power into difficult loads, even at
relatively low output-power settings (e.g. the 10-watt "tune" setting).

I've tried using this radio with an SGC longwire autotuner I picked up
for cheap at a hamfest, and have had great difficulty getting a
successful tuning. I hit the "tune" button, the radio starts
transmitting, and the autotuner simply chatters away indefinitely. I
can see the radio's SWR indicator bouncing all over the place, but it
never settles down and the tuner never "locks".

If I use the same autotuner, and the same antenna setup, with a
Ten-Tec Scout, the tuner will often achieve a successful lock on the
very same frequencies within 3-4 seconds, even though the Ten-Tec's
"tune" power setting is at the lower end of the SGC's tuning-power
specification range.

The TS-2000 has a high-SWR power scaleback. The Ten-Tec does not
(according to the manual it's SWR-protected in a different way). I
infer that the TS-2000 is probably varying its transmit power
constantly, as the SGC tries different matching combinations, and that
the rapid fluctuations in forward power are "confusing" the
autotuner's match-search algorithm.

So, it's entirely possible that Kenwood uses a transmit-power
throttleback algorithm which is sensitive to the output SWR, rather
than to the absolute level of reflected power seen by the finals.

--
Dave Platt AE6EO
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