[600MRG] Transmitting PA FETs ++

[Roger Graves]

Dave,

You already have a 200W amp that uses the IRFP450’s. Are you driving it hard for Class D? Is this not linear enough when driven at 100W SSB? Maybe increase the bias?

I have been checking mosfet specs myself looking for ones that might be good for linear operation with a pair providing 100W. It seems to me that ones with a low transconductance and large gate to source voltage range for the current range are desirable. 

The IRFP 450 is pretty good with a gfs of 9.6 and an aprox linear range within 1.0V gate swing, 190W.
IRFP240 has gfs of 6.9 with 1.0V aprox linear range, 150W, TO247 case
IRF520 has gfs of 2.7 and 2.0V aprox linear range, only 60W but several could be run in parallel.
The APT5020 is interesting if one can find them, gfs about 8, aprox linear range of 1.0V, 360W, TO247 case.
There are ones designed for linear RF operation, like MRFE6VP5150NR1, 950W, $50, 26 dB gain. Unusual case. Should be great!

Please keep us informed on what you learn about mosfets for linear operation.

73,
Roger



> On Feb 16, 2018, at 12:58 PM, Dave Riley <dave.riley3 at verizon.net> wrote:
> 
> I've been burning out linear and uber switching FETs for over a decade...
> 
> Have yet to settle on a favorite linear like a IRF510/20, what do you think??  I would like to ramp up to a linear 100W PA stage for ssb...
> 
> These IRFP450/460s will not burn out and they are cheap... Way lots of overhead ( almost goof proof ) and are still cheap to buy...
> 
> === 
> Rx noise figure... Back in the day a Western Electric 417A would yield 1.8db of noise figure but that is old stuff now... 
> What do you consider a good noise figure for your 630m front end?? Especially since most local line noises will cover up a 417A or even a 807 preamp... 
> Then again consider an e-probe way out in the woods, what would be better than a 310 fet??
> 
> http://www.radiocom.net/600M/417Aloop1.jpg <http://www.radiocom.net/600M/417Aloop1.jpg>
> ===
> 
> There is no more 20W erp on 600m ham so am planning to make a sine wave on 2200m and up with it...
> 
> What is conventional wisdom for PA power in to a decent transmit antenna??
> 
> See attached: http://www.radiocom.net/600M/SB600M3.jpg <http://www.radiocom.net/600M/SB600M3.jpg>
> This is a retired Heathkit SB600, will it make 1W eirp on 2200m??  SB2200m? TNX
> 
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