[Premium-Rx] Home-Brew Sync-AM Detector

[Gary Geissinger]

Guys,

One of the guys from work (Skip, K0UE) and I are working on the sync-AM
detector circuit that was given in the July 1993 issue of QST magazine.  I
got my copy of the article from Skip.  If you don't have access to this
issue we can probably fax or scan you a copy of the article.

I have mine built and tested.  While it isn't going to run Sherwoood out of
business (I still like my SE-3 better), it works very well and can be built
for about $50 in parts, including the "Bud box" case.

I can't compare it to a Kiwa sync-AM unit because I don't have one. (If
anyone has a Kiwa sync-AM unit for sale, please let me know!!!)  I have
compared it to a Watkins-Johnson HF-100, a Drake R8-B, and the Kiwa upgraded
Icom R-75.  The R8-B and Kiwa/R-75 receivers lock up a little easier, but
the fidelity seems comparable (no instruments, just ears).  The sync-AM in
the HF-1000 is just "okay" in my estimation.  Once this homebrew circuit
locks to the incoming signal, it really holds on.

The bottom line is that the "price performance ratio" make this circuit look
pretty attractive.  

I had to build a 20 dB attenuator into the IF input to make it compatible
with the IF output level of my receiver.  I used an LM386N-1 audio output
chip (separately derived 6VDC power, at a gain of 20) to drive a speaker or
headphones.

The reason I am bringing this up now is that the 455 KHz oscillator variable
inductor recommended in the article is being discontinued by Digikey.  They
sent me the notice yesterday.  This inductor is:

TOKO AMERICA INC
   Description: COIL 220UH TYPE 10EZ            
   Manufacturer Part No: RWRS-T1019Z                             
   Digi-Key Part No: TK1223-ND     

While there are probably a huge number of alternate inductors that would
work, this one is "just right" and costs $3.46 each.  Digikey had about 400
of them in stock yesterday when I checked.

The only other "sticky-wicket" is that the SA604 chip now is only available
in a surface mount package. Digikey and Emulation Technology (and no doubt
many others) sell pinout adapters that will convert this chip into a
standard 16 pin dual-in-line device compatible with easy breadboarding.  The
available part number is SA604AD.  There is another chip that should work
too, the SA614AD; it is pin for pin compatible.  I have some SA614AD parts,
but I haven't tried them yet.  The other 2 chips needed are of  the well
known NE602 type.

This has been the most fun $50 I've spent in a long time.

73's,

Gary WA0SPM

Gary A. Geissinger
Chief Electrical Engineer
DigitalGlobe
1900 Pike Road
Longmont, CO 80501
(303) 682-3826
(303) 682-3848 (fax)
ggeissinger at digitalglobe.com
"An imaging and information company"
see: www.digitalglobe.com

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