From: a-kevinp@microsoft.COM (Kevin Purcell, Rho)
Newsgroups: rec.radio.amateur.misc
Subject: NE602 RXes
Date: 12 Nov 92 00:39:10 GMT
Article-I.D.: ingate.9211111647.aa12545
Organization: UCSD Usenet Gateway
NNTP-Posting-Host: ucsd.edu
Originator: daemon@ucsd.edu

On Info-hams <auratek!epacyna@uunet.uu.net> said:

I have recently read several postings concerning the construction of simple
receivers. While these seemed to grow out of another subject, I thought that
the following would be of interest to those who might like to build a high
performance, yet simple, compact and low cost receiver. Block diagram follows.

 L/C Band---NE602 Mixer---Cohn Xtal---MC1350---NE602 Prod.Det.---LM386 AF Amp.
 Pass Fil.       |          Filter    IF Amp.         |
                VFO                                  BFO

While this is a traditional single converstaion superhet design, it uses only 4
IC's. I've built over 15 of these receivers (or in a transceiver) over the last

The IC's use very few external parts. The NE602 is a double balanced mixer with
internal biasing and on board oscillator/buffer. The MC1350 is a high gain wide
band amp with agc conrol. The LM386 is a well know part.

The crystal filter uses cheap micro processor crystals. It is a ladder network
with capacitor coupling. They are very easy to build. Band width can be changed
by changing the C value to cover CW/SSB. Make the filter with 12MHz crystals
and a 5MHz VFO = 40M (a 16MHz Fil and 5 MHz Vfo = 15M, 10MHz Fil and 4 Mhz VFO
= 20M etc,).

One example of a design can be seen in Ham Radio Magazine in an article call-
ed Micro-20 receiver (3 or so years ago). A PC board is available from FAR
Circuits (about $5) and its about 1 1/2" x 3".

--- end of quote

I've been thinking along the lines for a similar RX, but dropping the 1350 so:


 L/C Band---NE602 Mixer---Cohn Xtal---NE602 Prod.Det.---NE3352---LM386 AF Amp.
 Pass Fil.       |          Filter            |       AF preamp
                VFO                          BFO


more like a convertor in front of a "DC" rx. It seems that most 602 DC
RXes seem to avoid hum and microphonics so I would expect this to be an
OK design.

This has an advantage of putting a minimum amount of gain in front of
the product detector 602 which should preserve its dynamic range to
IN-band signals (signals really close to the one your interested in).
You can find with the top design that the AGC will either get rid of a
weaker signal in the precence of a very strong one, or if the IF gain
is manually controlled will result in a IMD products across the
passband from a strong in-band signal.

In the original version how did they derive the AGC? Was there a front
end attenuator (essential with a 602)? Did you use the on-chip
oscialtor or an JFET off chip (latter gives better harmonic performance).

Have you tried a similar design replacing the front end 602 with a
diode DBM (Mini circuits or homebuilt) or a balenced JFET mixer? Like so

           SBL-1/TUF-1
 L/C Band---DBM Mixer---Cohn Xtal---MC1350---NE602 Prod.Det.---LM386 AF Amp.
 Pass Fil.       |          Filter    IF Amp.         |
                VFO                                  BFO

This will probably need an extra IF stage just before the Cohn filter
to terminate the DBM for out of band signals?

What is you experience with NE602 DC RXes?

ANybody suggest a lower distortion part as a replacement for LM386 
suitable for driving Walkman style headphones.

Finally (begging part) is there any chance of getting a copy of the Ham
Radio article from you? None of the local libraries stock HAM Radio.

73 de Kevin Purcell N7WIM/G8UDP (Seattle, WA)          a-kevinp@microsoft.com
Do your interests match mine? If so call me. I'd like to hear from you.
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