> Yes, the broadcast 50 ohm load has a very low VSWR.
>
> Harris claims that with the 75 % RF efficiency, and only 25 % heat
> generation, it lets them to use air cooling.
> Individual new power supply for each module.
Right. My point is people seem to be reading the data sheet for the device,
which is a very confusing data sheet.
The data sheet, if read carefully, is for class-C pulsed duty with (I
think) 20% duty and 100uS pulse width. There is a small bit on pure class C
that might be carrier, because it says "CW". There are no linear mode specs
anywhere. Even the CW rating is at 75% efficiency, which means pretty deep
into class C and perfectly matched.
We cannot use class-C for HF PA's on CW or SSB. On CW it would have
terrible clicks. It would also require being perfectly matched (to maintain
that high efficiency). On SSB, it would have terrible splatter.
We'd have about 50-60% efficiency maximum for what we need to do, and that
is almost three times the heat for a given power. For 1250 watts output,
Hams would probably have about 2350 watts input and 1100 watts of heat.
Compare that to their special class-C test fixture, where for 1675 watts
input they get 1250 watts output with 425 watts of heat.
The linear Ham amp is over 2-1/2 times the heat compared to class C. This is
why, for amateur duty where it has to be linear, heat is a major issue with
a single compact device.
Also, and it is important to get this point across....... SWR claims for
high power devices in data sheets are just pure fiction, except in very
special cases that have nothing to do with real amplifiers we use.
73 Tom
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|