[Elecraft] SWR

[Don Wilhelm]

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