EMRFD Message Archive 11649

Message Date From Subject
11649 2015-09-23 16:28:56 Jim Miller BLF188 Class E?
I wonder if the BLF188 would be able to output a full 1.5KW if run in Class E rather than linear where it is limited to 1KW.

With a modulated supply it could do SSB etc but for 6m EME use and JT65 the straight Class E should be fine.

It is insanely rugged. Check out the Youtube videos of it.


jim ab3cv
11653 2015-09-24 05:21:28 kb1gmx Re: BLF188 Class E?
Look at the input and output capacitances as well as the saturated resistance (RDSon).
First you have to find those parameters as that MOSFET is not designed for that mode.  
That will also define the drive needs.  

The answer is likely yes but not easily at 6M.  

The other thing is class E envelope restore is a very touchy system as you also have 
to maintain phase relationships or the result is not very good.

But a pair of them with a simple Wilkerson splitter and combiner will do that easily
as a linear with plenty of headroom and low drive requirements. The TV and FM 
industry has been doing this for years and the results are good.  Much easier than 
trying to modulate a 40A 50V supply.

I've done that in small scale using a pair of MRF492 combined.  The result was both
rugged and reliable at 200W using a manageable 13.8V supply. Considering that's
and old bipolar device not know for being super rugged its proven itself in actual 
use into shorts, opens and the usual field day stuff.   Next step is a pair of BLF278s 
combined if I ever have the need.   So far the need for more on 6 has been satisfied 
with bigger antennas, that's cheaper gain.


11654 2015-09-24 07:10:36 nm0s_qrp Re: BLF188 Class E?
Yes, it looks doable.  Run 30v on the drain supply, and you should be able to get about 80% efficiency from it.  Sounds like a fun project.

73 Dave NM0S