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Old 8th Dec 2017, 12:55 am   #10
Herald1360's Avatar
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 12,330
Default Re: 'Kalmus' wideband RFPA: info.?

Originally Posted by Skywave View Post
Originally Posted by Herald1360 View Post
+/- 2dB gain flatness in a 50W amp used as an RFPA for transmitting could be a pain - power out could vary between 50W and 20W whilst still being "in spec" for a particular input level.
By my arithmetic, +2 dB on 50-watts is 80-watts; -2 dB on 50-watts is 32-watts (all to nearest watt). So the output could vary between 32 to 80 watts. OTOH, 20-watts to 50-watts is a change of +4dB. But that corresponds to a gain variation of +4 dB / -0 dB. That is not the same as 2 dB.

I was assuming that the amp was unlikely to produce MORE than 50W at any frequency, so given a dose of typical specmanship, gain "flatness" is just that- you can draw a straight line at 2dB down from 50W and the output would vary no more than 2dB above and below when a constant drive level is applied. It could be driven harder to get 50W at a low gain frequency, but doing the same at a high gain one would overdrive it with consequent seriously distorted output.

Another way to look at it would be- At some (carefully selected) frequency in the operating range it will need a particular drive power, P. To get 50W output anywhere else in the operating range, P will vary by no more than +/- 2dB from its original value.

Maybe I'm a bit cynical, but..........

Re Jeremy and power measurement- doing it calorimetrically is one way to know just how much altogether is coming out.
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Last edited by Herald1360; 8th Dec 2017 at 1:07 am.
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