Wes,
An analog open loop ALC is one in which the drive is reduced in response
to an overload condition (high SWR, power level that exceeds the maximum
set level). The response is applied only after the offending condition
occurs - that is an open loop system.
With the K3, KX3 and K2 power control system being a closed loop system,
that condition does not exist. The overshoot possibility is detected
early and the power is reduced accordingly without PA overshoot and the
PA going into a distortion region.
If you have any understanding about closed loop control systems, you
will then understand 'damping' conditions. Underdamped systems will
oscillate near the 'set point' while overdamped systems will never come
up to the set point. Critically damped systems will quickly settle to
the set point and maintain the proper condition (power level,
temperature, you 'name it' condition). In the case in point, the power
level is the 'set point' that is considered. An open loop system is
totally undamped and will only respond 'after the fact' to conditions
that exceed certain thresholds. Closed loop systems approach those
thresholds with actions that will result in critical damping of the
response mechanism.
73,
Don W3FPR
On 2/12/2015 11:05 PM, Wes (N7WS) wrote:
I realize all of that. But it's still an analog PA. What is an
analog open loop ALC?
On 2/12/2015 8:59 PM, Don Wilhelm wrote:
Wes,
That is true, but the control of the drive to that analog PA is
different than that implemented in transceiver that use analog open
loop ALC and SWR power reduction. The K3 (and K2 and KX3) do ALC
differently than other transceivers. You may find similar systems in
commercial transceivers, but I don't think the same methods are
employed in any other amateur transceiver.
73,
Don W3FPR
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