Dave Platt wrote:
Does anyone have any schematic for Direct Conversion receiver that does not
use any FETs, Valves or ICs (e.g. NE602) but uses NPN transistors?


"Experimental Methods in RF design", section 1.8, page 1.13, has the
schematic for a DC receiver which uses NPN transistors throughout most
of its design (including the product detector). Tuning is done via a
varactor-based VCO - you might be able to substitute a reverse-biased
junction in an NPN transistor for the varactor.

There are two ICs - an LM7805 voltage regulator (for which you could
probably substitute a shunt regulator such as a zener diode or an NPN
transistor wired up as a Vbe-multiplier) and an LM386 audio amplifier
(for which you could substitute the discrete-NPN audio amp design on
the previous page of the book).

I'd say there's a good chance you could modify this design so that
every single semiconductor in it was an NPN transistor such as a
2N3904 or 2N2222 or a similar jellybean.

-- or for the shunt regulator you could use a back-biased base-emitter
junction in a 2N2222. It trashes the transistor, but it makes an
adequate zener.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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