[Elecraft] Interpretation of P3 display

[Jim Brown]

On 6/9/2012 5:14 AM, Geoffrey Mackenzie-Kennedy wrote:
> the reason why a typical ALC can be responsible for splatter is because
> these ALC systems sample the output of an amplifier and/or exciter, and due
> to time delays cannot "throttle back" the drive power immediately.

The ONLY proper ways to set power output are 1) to turn down the 
transceiver's output power by turning down the power control on the 
transceiver; or 2) using a resistive attenuator (voltage divider) 
between the transceiver and the amplifier.  W8JI, who has designed a lot 
of power amps, and, as part of that design work, has studied the 
behaviour of lots of ham transceivers, has written an excellent and 
detailed tutorial on this matter, and on how some ham transceiver ALC 
systems badly misbehave, and NEED to use option 2.  The K3 (and the 
FT1000MP)  do not have this problem, and work fine with option 1.

ALC from the power amp to the transceiver should NEVER be used to set 
transmit power, for the reasons you've noted. It is provided for on most 
ham products because many hams think they need it.  If used at all, 
transceiver output level should be set so that ALC ONLY protects the 
amplifier by backing off the drive when something in the antenna system 
breaks, creating a load that the power amp is unhappy with.

Note also that this advice is NOT new, and applies equally to old power 
amps.  I first saw this advice in the manual for my 35 year old Ten Tec 
power amps.

73, Jim K9YC