[GreenKeys] Loop Keying Transistors

[Bob Camp]

Hi,

Not having stirred up enough controversy yet I have decided to attack 
on another front ...

For years and years I have used MJE340's as loop keying transistors 
both for 20 and 60 ma loops. I have used them both with high voltage/ 
resistor loops and with constant current loops. They have always worked 
just fine. They are still available and they are cheap. All that said I 
decided to take a look at some alternatives.

Fairchild makes a couple of 400 Volt TO-92 package power mosfets. They 
have 20 or 30 volt gates on them and will handle at least as much 
current as a MJE340. The best of the bunch appears to be the SSN1N45B. 
It's rated for a half amp and 450 volts. They are rated for inductive 
load switching and *appear* to be rated for a 60 mill / 4 H loop at 100 
wpm. With a 0 to 10 volt signal on the gate they should do a fine job 
of keying a loop.  The price seems to vary from about 17 cents up to 28 
cents depending on where you look. They are on the sample program from 
Fairchild so they may even be available free .... (free is good ....).

None of that is going to get me to tear out the MJE 340's and stuff in 
mosfets. However I may try them out in what ever I wire up next.

	Enjoy!

		Bob Camp
		KB8TQ