Please refer to the Flex hardware reference manual regarding ALC:
"Please note this input is provided as a safety measure for external amplifiers. It is NOT meant to be used in regular operation as an active power control input or to modify the “attack” of an external amplifier."
So I do not believe that the ALC implemented in the Flex-6000 radios will do what you want.
If ALC is setup correctly you will get maximum power from the amp.
The settings you have are exactly as SPE recommends...
Using ALC operates exactly the same as turning down your power manually. The only difference is the amp provides feedback to electronically control the output power of your transmitter.
SPE recommends running your transmitter at full output and let the amp turn down power using ALC.
The only thing I can figure is the flex using 0 to -4 v and the SPE uses 0 to -11v but to me that seems the opposite problem would happen. You would get too great an output.
I am curious, if you leave ALC on but back down the power on the Flex (which you should have have to do) is there a sweet spot were the amp outputs full power ?
Dr Gianfranco of SPE claims that the Expert Amps have intelligent ALC that can accomodate any level of ALC. He also claims that his version of ALC does not cause distortion because it is intelligent. I have not tested his claims..
I suspect that your real problem is likely that you are getting RF into the ALC Cable which is totally screwing up the ALC action. As further evidence of the RF into the ALC cable issue, the fact that when you reduced the drive power the problem was somewhat mitigated would be pretty conclusive evidence that you have an ALC Cable RF problem
First Solution.. Put Ferrites on both ends of the ALC Cable.
Better Solution: Forget about using ALC altogether.. Use Autodrive via DDUTIL to set your input power levels. and then you never need ALC...
The latter is how I run my 2K-FA
I write to SPE TECH STAFF and I have this answer:
I could not help testing instrumental with Flex-6500, but 'I assume that the entrance of this transceiver ALC is too "slow" and therefore not in phase with the actual level of RF energy.
This would explain the wide fluctuations of power detected.
Obviously this 'involves the inability' to include such an ALC in a loop for dynamic control of the pilot, used in amplifiers of the series Expert and beyond.
Reading the manual FlexRadio downloaded from this address,
on page 39 and 'written quite clearly that this input ALC should not be used to limit dynamically the power emitted.
Vy 73s DX
Ing. Marco Vona (IW0FFK)
S.P.E. Societa 'For Elettronica srl
Now I wonder what is the use of flex 6500 ALC????
Best 73 IZ7AUH