[Elecraft] Power Settings for no AGC in Elecraft Radios

[Joe Subich, W4TV]

 > Are there other radio brands with power control loops like Elecraft
 > products?

I know of no amateur transceiver that uses the same approach to power
setting as Elecraft but it is common in commercial transmitters.

 > I accept this, but don't quite understand the reasoning.  Don can you
 > please explain the key differences between a rig, such as my Icom 746,
 > and the K2 that mandate this?

Elecraft *measure* the gain of the driver and final amplifier when
calibrating and set the IF output to the level necessary to drive the
amplifiers to the desired power output.  Other amateur transceivers
simply measure the level of grid/base/gate current of the final
amplifier and reduce gain in an IF amplifier to prevent the current
from reaching an "overload" point.  The problem with the typical "ALC"
circuit is that the excess current level must be exceeded before the
IF gain can be reduced *and* that point is dynamic which means the
ALC action introduces distortion by its very nature.

The Elecraft ALC is not a "feedback" design - instead it acts on the
audio input to slowly increase/decrease the IF output to the proper
level for the desired output.  The K3 "ALC" indicator serves two
purposes - below the nominal "five bars" it shows expansion (additional
audio gain) needed to bring up the output level and above that it shows
the gain reduction used to prevent the driver/final from being driven
beyond the desired power level.

By knowing the gain characteristics of the driver/final *on each band*
Elecraft are able to prevent problems like the "power spike" and
"flat-topping" inherent in the feedback design.  The modulator output
is set on each band for the exact level needed for the desired output
power.  Unless the user changes the input level (too much audio) the
K2/K3 will not flat-top or spike and the gain does not "hunt" and thus
cause additional transmit IMD..


73,

    ... Joe, W4TV



On 7/5/2012 8:46 PM, John wrote:
> All (especially Don),
>
> I have heard it explained on this reflector the Elecraft power control
> loop is such that the usual advice to...
>
>     "max out the power setting and adjust the audio level input to avoid
> AGC action"
>
> ...is not appropriate for the K2 and, I suppose, the K3.
>
> I accept this, but don't quite understand the reasoning.  Don can you
> please explain the key differences between a rig, such as my Icom 746,
> and the K2 that mandate this?
>
> Are there other radio brands with power control loops like Elecraft
> products?
>
> Thanks.
>
> John, kx4o
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