On 7/7/2012 1:18 PM, Bruce wrote:
> Hi Tom,
>
> The new Harris Flexiva 10 KW FM band (not pulse) stereo transmitter is not
> having a heat problem with air cooling, in a reasonably small package . It
The problem with starting with a saturated amplifier and then
backing off the power for linearity is that the dissipation actually
goes UP when you reduce the output power. The maximum dissipation
occurs at something like 1/3 of maximum power. Therefore, this FM
transmitter is not really proof that a linear amplifier is practical.
I have done a lot of work with Dick Brounley's laser drivers. He
gets up to 750 watts (continuous duty) out of a pair of MRF150's
at 81.36 MHz, just below the FM band. Dick's design is great for
its intended application, but doesn't translate to a ham amplifier.
Furthermore, it is water cooled. The biggest problem Dick has
thermally is cooling the ferrites in the output transformers.
He actually has to heat sink them with copper sleeves.
RF lasers are lucky to have 10% efficiency in terms of converting
RF to light. Therfore, they are all water cooled and this makes water
cooling for Dick's amplifiers basically "free".
Rick N6RK
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