A further consideration has to do with what kind of AMU you are using,
whether electronic or mechanical (for want of a better description).
Once a match is memorized, electronic AMUs set their solutions nearly
instantly. High SWR levels exist only for milliseconds (if that).
But mechanical AMUs (whether automatic or manual) require TIME in order
for the capacitor(s) and inductor to find their proper matching
positions. Even when a match has been previously memorized, it may take
several seconds for the inductor wheel to traverse the roller coil and
the capacitor(s) to rotate.
That's why one needs to pay attention to the SWR levels impacting both
the AMU and the transceiver.
73,
Kent K9ZTV
On 9/12/2020 6:03 PM, KENT TRIMBLE wrote:
Alan is right, but it depends on which "good book" one is consulting!
We have to be careful about transceiver power levels when tuning an
external AMU, for the sake of the /transceiver /as well as the AMU.
Your AMU may be able to tolerate 100 watts during the tuning process,
but your transceiver may not. Unless the transceiver automatically
folds back its output in the presence of high SWR levels, one risks
damaging the transceiver's PA transistors. While many modern rigs do
so, others, especially older rigs often used by new licensees, do not.
For example, when seeing an SWR above 3:1, my FT-991A reduces its CW
output from 100 to 10 watts while at the same time flashing "HIGH SWR"
in red letters. The rig may be successfully protecting itself, but
why risk stressing components if it's not necessary? That's why I
prefer switching the transceiver to AM at 25 watts when tuning an
external AMU.
73,
Kent K9ZTV
On 9/12/2020 5:16 PM, Alan - G4GNX wrote:
Although it's preferable to have at least 20W to tune, the good book
says that anything between 7 and 100 watts is OK.
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