A linear does not demand constant gain at any power level, within the
context of this discussion, which is clearly concerned with
intermodulation products, and is therefore related to non-distorting
dynamic range, somewhere, of the transmitting amplifier.
Constant gain is only of relevance if AMPLITUDE linearity is a concern.
> Earlier, Rich served an ace with his point that a linear amplifier
> demands constant gain at all signal levels.
Rich simply duped the spectators at the tennis match, the ball was
out.....
> Because the gain depends on
> the 3/2 power of the screen voltage, as Rich said, the transfer
> characteristic of the G2DAF-type amplifier cannot be a straight line. It
> has to be S-shaped - starting with low gain at low signal levels (and
> therefore low screen voltage), increasing for medium levels, and then
> flattening off like any amplifier does if over-driven.
Seems that Daffy already had his eye on the audio compressors built into
modern rigs to handle the possibility of "low" drive levels?
> This might explain why the two-tone results from DAF-type amps can look
> reasonable at high (but not excessive) drive levels. At lower drive
> levels, the IMD relative to the output level could be significantly
> worse. An oscilloscope pattern of the two-tone signal would presumably
> show significant "pinching" of the crossovers as the gain drops...
Is this possible crossover "pinching" manifested as reduced amplitude,
or waveform distortion produced by too low a drive level? If it's the
latter, then presumably it's irrelevant as the amp is not producing any
power.
> but
> the output level is lower, so maybe it matters less? What this means for
> a real-life speech signal is hard to guess.
>
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.demon.co.uk/g3sek
>
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