> From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
> To: amps <amps@contesting.com>
To: <amps@contesting.com>
> Date: Tue, 17 Jun 97 12:28:00 +0000
> The basic idea is that if you have a telephone channel and you load it
> up with white noise, the IMP's will appear as noise. If you put a notch
> in the middle of this band input of noise, IMD will cause products to
> appear and 'fill in' the notch when you look at the output.
Excellent. I follow the idea now. You notch a narrow frequency area
of the output of the white noise generator, and see how much the PA
fills in that area.
By the way, I hope no one has been confused by the posts on tubes.
Certain tube types do work better than others in some applications,
but it is VERY important to remember carte blanche self-made
"rules" of low mu only being grid driven and high mu being only
cathode driven or having restricted class of operation is incorrect.
It is true with anode voltages down in the knee of the constant
current curves an 8877 will draw 600 mA of grid current if the grid
is biased to 65 volts positive, but in normal operation the gid
current is very low. Anyone operating an 8877 PA, and comparing that
PA to one using unfocused tubes like the 3-500Z, will notice the
large grid current difference.
Contrary to "claims", it's possible to get over 600 watts of RF out
of a class A or AB1 8877 PA, and the tube can be grid driven just as
a low mu tube can be used grounded grid.
73, Tom W8JI
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