The 1 db compression point is usually concerned with input power to an
amplifier. Usually a receiver front end or preamp.
You usually want to know how big of an input signal the amp will handle
before compression starts. The 1 db figure is a common reference point for
amplifier comparison. Those amplifiers are class A very linear amplifiers.
Our typical ham power amplifiers have nowhere that kind of linearity. If you
were to plot output verses input on most amps you will find that it swings
around quite a bit as drive is increased. Compression at the high end can
be a surprising amount.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jim Thomson
> Sent: Wednesday, June 30, 2010 7:40 AM
> To: amps@contesting.com
> Subject: [Amps] 1 db compression point procedure ?
>
> Ok
>
> What's the exact procedure for finding the ..'1db compression point' on
> a HF amp ??
>
> I have conflicting info on the procedure. With hardly any drive, the typ
> HF amp has a
> lot of gain. As drive levels increase, the gain goes down. Question
> is.... where is the
> starting point of all this?? With 1 watt of drive... or 5w or what ?
> It makes a big diff
> to the results.
>
> I'm assuming the amp is 1st tuned to say normal power output... like
> 1200-1500w out..
> IE: tune and load tweaked for max power out at normal power, then maybe
> increase the
> loading a tiny bit [ slightly more Un meshed].
>
> Then leave the tune and load caps alone... and reduce drive to a very
> small amount... and then measure
> both the drive to the amp... and also the power output of the amp [ say
> 1-5 w of drive.. and 20-100w out]
> Then start increasing drive level a bit and measure the gain once more
> [ it should be dropping off a bit]
>
> Does this procedure have to be done with a cxr.. or can we do it pulse
> tuned ?? Have I even got the
> procedure any where near correct??
>
> I take it, we don't want to operate the amp beyond the point where the
> gain drops by 1 db ? But
> where is the starting point ?
>
> I can also tweak the bias on the GG amp quite a bit.
>
> tnx.... Jim VE7RF
>
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