[1000mp] Re: Mark V Field Power Output Mod

[Joe Subich, K4IK]

Mike, 

> I think the Toshiba 2SC2897 IMD Po curve speaks for itself, 
> but a few extra words about it won't hurt.
> 
> There is a world of difference with IMD numbers ranging from 
> -38db to -24db, the change from 60 watts to 100 watts.  The 
> idle current was set to 100ma, in the test set up.
> 
> The factory apparently sets the radio at 50 watts output per 
> transistor, or IMD numbers of approximately -35 db.  Therefore 
> operation at 100 watts per transistor, degrades IMD performance, 
> with this circuit configuration, by a factor of approximately 
> 10 times.

The Field is operating very close to the point of minimum IMD.  
If you look at the test circuit, it does not contain much of 
any output filtering - just an impedance matching "L" network.
Since most practical lowpass filters  will have on the order 
of .6 dB to 1 dB of insertion loss, I'd estimate the push-pull 
pair of transistors in the Field is actually generating about 
115 watts at the collector to make 100 Watts at the output 
connector.  That would set the IMD at around -36 or -37 dB.  
The output of the radio can't be controlled any more closely 
than that. 

I stick by my original comment, anyone who would run a Field 
at 150 or 200 watts is the same kind of immature, sick person 
who would illegally "hotrod" a CB radio.  BTW, Texas Star (one 
of the biggest trash peddlers) uses four 2SC2897s in their 350 
Watt "export" amplifier - need I say more? 

73, 

   ... Joe, K4IK