RadioBanter - View Single Post - Another Dallas Lankford article on synch detectors

[email protected] · August 2nd 06, 01:03 AM posted to rec.radio.shortwave

wrote:
Joe Analssandrini wrote:
Hello,

I do not know Dallas Lankford's e-mail address so I should like to make
a comment here in the hope that he will see it (or that someone will
forward it to him).

As a "program listener," I disagree with his overall assessment of
synchronous detection circuits in general as I find that even the
weakest one I own (on the Sony ICF-SW7600GR) is far more useful than
not in making SW (and MW) signals more intelligible and listenable.
However, be that as it may, and we are all entitled to our opinions of
this circuit (and it is obvious that Mr. Lankford knows what he is
doing so I accept and respect his opinion), I must strongly disagree
with his assessment of the AOR AR7030 Plus' synchronous detection
circuit and his characterization of it as being "unacceptable."

He is quite right, of course, when he states that the AOR's sync
circuit often will not lock by itself on a VERY weak AND fast-fading
signal (is there any sync circuit that will?) but there is, in fact, a
"trick" to get it to do so.

I control my AR7030 Plus with Jan Arkesteijn's "RxWings" - a free
computer-control program. As is known, when using the AOR with the
remote or the radio's tuning dial, and changing stations, the sync
temporarily turns off and then relocks (or attempts to) on the new
tuned frequency. If tuning to the type of signal mentioned by Mr.
Lankford, the radio will not re-lock, but, if using "RxWings," the sync
circuit never shuts off.

In other words, all one has to do is to engage the sync lock on any
relatively strong signal and then tune, via "RxWings" to the desired
(very weak and fading) station. The sync circuit will maintain lock.
Indeed, in over two years of ownership, once locked, my particular unit
has NEVER lost lock under any circumstances whatsoever! (Of course I
use the AUTO setting exclusively with the sync.)

I believe that the AOR AR7030 Plus synchronous detection circuit is a
superb one and is one that greatly enhances the listening experience.
At least it does for me!

I hope this is of some use to all in general and to Mr. Lankford in
particular. I also want to thank Mr. Lankford for his excellent and
thought-provoking article. I hope to see more along these lines from
him.

Best,

Joe

Pete's Analog Devices AD607 based receivert will track down below
the audible noise floor. On MW the AD607 is generally "better" as in
"will
track rapidly fading stations with multiple stations in the back ground
with
no, or very few growls" then AOR's in any position.

However the "improved AM detector" at
http://www.amwindow.org/tech/htm/alowdisdet.htm is about 95%+
as effective and never growls. And is a lot easier to build!

Those precision diode circuits date back to when op-amps were
expensive. When you need such a circuit on a chip (where floating
diodes don't come easy), you simply switch between an inverted and
uninverted signal path using analog switches. A comparator controls the
switching. It's an extremely high linearity design since no diodes are
in the signal path. It's similar to a sychronous rectifier used in
power supply design.

Thanks for the name of a control program for The AOR, since I will only
have it
for another 3 or 4 weeks, I didn't want to spring for a "real", as in
commercial,
software. I didn't realise the AOR acted differently under PC control
then
the local controls.

If I ever win the lottery, unlikely as I don't buy tickets, I would
love to buy at
least one of every major AMSD equiped radio, a Kiwa MAP, and the
Sherwood
SE-3.

I have come the conclussion that a good IF filter makes more difference
then the detector.

Terry