"Michael Black" wrote in message
mple.org...
On Fri, 16 May 2008, Scott Dorsey wrote:

Richard Knoppow wrote:
It seems to me that it should not be too difficult
to
design one that is superior to the old vacuum tube
models.
There are certainly plenty of receivers out there which
could use an adaptor. Have you any definite ideas about
price range, features, etc?

What I was thinking was to take the AM synchronous
detector circuit from
OH2GF which was published in the July '93 QST issue. It
is based on an
NE602 which does not have the best dynamic range in the
world but seems to
be okay.

A slicer by definition has selectible sideband, and maybe
specifically uses phasing to get it.

They existed at a time when there wasn't much but AM
radios, so to get
around the "turn down the RF gain, turn up the AF gain and
turn on the
BFO" you needed to add a product detector. Once you were
doing that,
you might as well add selectable sideband via phasing,
since it didn't
add that much to the cost, but did help improve things
when the receiver's
IF was wide for AM.

It lives on today, since most "low end" shortwave
receivers that have
synchronous detector uses the phasing method to increse
performance
without the cost of an actual better IF filter.

There were external SSB adaptors that included an IF
filter for SSB,
but I can't think of seeing any that called themselves
"slicers".

Michael VE2BVW

I was first going to make up a PC board layout rather
than constructing it
dead-bug style like the original, then I was going to try
one of the new
Maxim detector chips in place of the NE602, but retaining
the NE804 limiter
and phase detector.

If I were going to do it with tubes, I would look into
some of the sheet
beam tubes that were intended for TV chroma detector
circuits... many of
them have excellent performance and are very inexpensive
(as are all old
TV tubes). The 7360 costs a bloody fortune when you can
find one, but
the 6AR8, 6JM8, and 6ME8 are effectively the same basic
design but with
less crosstalk.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I am not sure how a synchonous detector works with
suppressed carrier SSB but my understanding of it may be
incorrect. To me a synchronous detector is a device for
replacing the carrier of a double sideband signal, either AM
or suppressed carrier and synchronized by means of the equal
and opposite phase of the two sidebands. Such a detector
will supply a locally generated carrier which has exactly
the right phase with relation to the sidebands even when
they are distorted by selective fading. Similar detectors
are also used for television where there is a residual
carrier and sideband since that is enough to lock the
oscillator to the correct frequency and phase.
Beam switching tubes were used to some extent in
commercial vacuum tube equipment but Hallicrafters
transmitters are the only example with come to mind at the
moment, I am sure there were others. These things came along
at about the same time that transistors began to supplant
tubes.

As far as selectable sideband in an SSB adaptor AFAIK
all worked by means of either shifting the signal to the
filter frequency or having two filters. I don't see how
phasing would work in a receiving adaptor. There were
numerous phasing type SSB generator for transmitting, for
instance the one made by Barker and Williamson who also made
90degree audio phase shifting networks for use in home made
ones. I still have the B&W adaptor I used in the 1960s. It
worked pretty well but had to be adjusted for any large
frequency change. Stable high performance filters or
reasonable cost pretty much ended the use of phasing type
exciters.

In any case, a good performing receiving adaptor which
would work on older receivers, especially tube receivers,
would be welcome. The old Hammarlund and TMC units are
pretty hard to come by and, I suspect, something modern
would outperform them.


--
---
Richard Knoppow
Los Angeles, CA, USA

WB6KBL