[Elecraft] Interpretation of P3 display

[Adrian]

What have these last few posts got to do with interpretation of the P3
display?

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Geoffrey
Mackenzie-Kennedy
Sent: Saturday, 9 June 2012 10:14 PM
To: Elecraft Discussion List
Subject: Re: [Elecraft] Interpretation of P3 display

Fred and Van,

Some comment follows.

On June 09, 2012 at 7:03 AM, Fred Jensen K6DGW wrote:

<snip>


> OK Van, multiple questions.  What most folks call splatter is caused 
> by driving the last amplifier stage into saturation [i.e. it can't 
> produce any more power so it clips off the peaks].  It doesn't really 
> involve compression, they're just driving their amplifier into 
> saturation, it clips the peaks [a very non-linear occurrence], and all 
> sorts of IMD is generated around their signal.  The cure is, "Don't 
> drive your amplifier into saturation."  This is sometimes called
flat-topping.

Fred, although IMHO your advice is sound, please don't forget that prime law
of physics which states that "Garbage in will result in Garbage out". 
Overdriving any amplifier in an exciter used to drive an amplifier (with
some exeptions e.g. most pre-filter amplifiers) will result in splatter
being transmitted, even if the final amplifier is squeaky clean and linear
at any output power level.

My intention for saying this is that the typical ALC arrangement is often
incorrectly used as a means to control the level of power output from the
exciter and/or amplifier to some chosen level, rather than as a protective
device, and can be responsible for splatter.

Van, the reason why a typical ALC can be responsible for splatter is because
these ALC systems sample the output of an amplifier and/or exciter, and due
to time delays cannot "throttle back" the drive power immediately. As a
result a burst of excess drive power can be produced, especially during
voice peaks, which can result in some amplifier(s) in the transmitter chain
being overdriven and creating splatter. There are types of ALC system used
which do not create this problem, but that's another subject.

73,

Geoff
LX2AO











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