NE602s are indeed simple, but a poor choice for a direct conversion
receiver. It's really important for a DC receiver mixer to retain good
linearity and balance with large signals. Otherwise, strong AM signals
will be demodulated and their audio will appear in the background (or
foreground!). Doubly balanced mixers like the SBL-1 or one you can
easily make from a couple of ferrite cores and 4 silicon or hot carrier
diodes are much less sensitive to this problem than an NE602. In some
circles, DC receivers have a bad reputation, and one reason is that
people aren't aware of this problem so use inappropriate components.

The problem is particularly acute on 40 meter, which it's difficult or
impossible to filter out strong AM broadcast stations before they get to
the mixer.

Roy Lewallen, W7EL

John R. Strohm wrote:
"Joshua P Luben" wrote in message
...

Get a CD-ROM from ARRL of the past few years QST articles. There are some
pretty simple to build receivers and transmitters.

Then get yourself an ARRL handbook, it will be your best reference for a
long time to come.

Since you're just begginning, start simple. Work on direct conversion
receivers using SBL-1 mixers and LM386 audio op-amps. Keep them simple;

once

you get one working, tinker with it, add on to it. Most importantly, if it
doesn't work--ask very specific questions.


NE602 front-ends are even simpler than SBL-1 front ends. Contrary to
popular belief in some circles, you can still get the NE602 in 8-pin DIP,
new, from Philips: the new name, for an improved part, is SA612AN. (The N
suffix means 8-pin DIP.)

You can find most of the "Amidon" toroids on eBay: the key is to search for
MicroMetals (the actual manufacturer). www.kitsandparts.com also sells the
popular toroids in 25-count quantities, for CHEAP.

Ocean State Electronics has a lot of useful stuff. www.oselectronics.com (I
think).

I'd add a copy of "W1FB's Design Notebook" to that CD-ROM and the ARRL
Handbook. If you can find DeMaw & Hayward's "Solid State Design for the
Radio Amateur", grab it. Check www.qrpbooks.com; they may still have a few
copies.