On Mon, Feb 01, 2010 at 03:31:56AM -0500, Roger wrote:
>
> Rob Stampfli wrote:
> > On Mon, Feb 01, 2010 at 12:50:25AM -0500, Roger wrote:
> >
> >> I'll admit I've not seen them all but I've never seen a transmitter
> >> where I couldn't vary the output.
> >
> > Take a look at the Kenwood TS-430S, a rig that was marketed as late as
> > the mid-1980s: It has a carrier control, allowing the power level to
> > be controlled for CW ops and partially for AM, but the only voice level
> > control is the mic gain. FM is also fixed at about 40W.
>
> You have a point with FM, but I figured the mike gain was all that was
> needed.
>From a practical perspective, it is all but impossible to use the
MIC GAIN control to limit PEP output power to a desired value.
The reason is that there is no feedback involved with the MIC GAIN
setting -- it just sets a given level of audio amplification -- and
any PEP limit is therefore soft and can be overcome just by talking
into the microphone a bit louder.
What you really need for PO control is the ability to adjust the point
at which the rig's ALC action commences. The 430 has an internal
adjustment for this -- set to allow the rig to put out 100W -- but
nothing that is readily accessible or adjustable on a routine basis.
Interestingly, my 430 interoperates quite well with the AL-80B for
FM operations: In FM mode, the 430's ALC level still affects PO,
so with an ALC connection between the rig and the amp, the ALC SET
control on amp can be used to dial the exciter output down to QRP
levels.
Unfortunately, for voice, there is enough hysteresis in this ALC
feedback loop that effective PO control is largely ineffective in
rapid onset audio conditions, resulting in brief excursions to 100W
PEP signals from the 430 regardless of the amp's ALC setting. Thus,
mating the 430 with an amp for SSB operation can be problematic if
you want to limit the amp to less than 100W of drive.
Rob / KD8WK
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