[TRLog] Need help with Keying/PTT/Paddle interface

[Michael Tope]

Good point - the darlington adds one diode drop to 
the Vce saturation voltage! Exactly how low do the
modern transceivers need to go anyway? One would think 
that pulling them down to 1 volt would do the trick.
Guess not, or is the strobe driver adding more voltage
drop as Tree's post suggested?

Mike, W4EF...........

----------
From: 	George Cutsogeorge[SMTP:w2vjn@rosenet.net]
Sent: 	Tuesday, January 26, 1999 12:00 AM
To: 	Michael Tope
Subject: 	Re: [TRLog] Need help with Keying/PTT/Paddle interface

The darlington has more drop than a single transistor and may
cause trouble with some radios.  A better choice is a power MOS
FET as it draws no input current and has very low output drop.  A
suitable type is the VN10KM or the 2N7000.  They are designed to
saturate with a TTL input level.

George
W2VJN


-----Original Message-----
From: Michael Tope <W4EF@pacbell.net>
To: 'Pete Smith' <n4zr@contesting.com>
Cc: 'TRLOG' <TRLOG@contesting.com>
Date: Monday, January 25, 1999 7:11 AM
Subject: RE: [TRLog] Need help with Keying/PTT/Paddle interface


>
>Has anyone tried a darlington pair (beta multiplier)
>in place of the keying transistor? This should draw
>very little current from the interface.
>
>Mike, W4EF
>
>----------



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