Thanks John...........that will be good.

Pete

John Crabtree wrote in message
...
"Pete KE9OA" on 12/30/03 wrote:

I am not sure how to do the selectable sideband function, but
I can figure it out, I will sure throw that function in. I just
ordered some samples of the high speed op-amp that is used
for squaring up the signal to the phase detector. They should
be in on Wednesday. I am doing two versions of the
detector...........one of
them will use an AD op-amp, while the
other will use a Burr-Brown device. This sync detector will have
two ceramic bandpass filters in the signal chain.........one of
them will be between the mixer output and the I.F. input, while
the other will be between the I.F. output and the demodulator
input. It shoud be a low-noise system. AD specifies this
configuration as having an MDS of -90dBm. I will be feeding in
a -20dBm signal, so the earlier stages of the receiver will have
more than enough takeover gain. If there is enough interest in
the circuit design, I will post the AD application note up on my
website.
Thanks for encouragement!

Pete

You have some options as to how to provide selectable sideband in the
synchronous detector:

1. You can do it with passband tuning and move the signal carrier to the
edge
of the IF filter passband. IIRC this is the way that you can select the
sideband in the AOR7030. I suspect that doing this will cause some phase
distortion to the carrier if you place it on the edge of the passband. To
what
extent this matters I do not know.

2. Once you have the I and Q signals from a quadrature detector, you can
use
all-pass networks to phase the outputs and then add or subtract as
necessary.
Sony did this with the ICF-2010. Trevor Brook in his Electronics and
Wireless
World article did this as well.

One issue with this approach is that the level of opposite sideband
reduction
is dependent upon the quality and number of stages in the phasing
networks.
IIRC Sony only achieve ca. 25db of opposite sideband reduction. The
quality of
phasing networks has been discussed in the ham radio literature re. the
generation of SSB signals. It is possible to design simple networks which
are
'OK' over the range 300 to 3000Hz.

Once you have the Q output, it then should be very straightforward to
offfer
quadrature detection as well, where you null out the strongest station on
the
frequency to which the detector has locked.

Which ever way you might choose, there are inevitable compromises.
Another
issue is what audio bandwidth is necessary in an AM receiver. Some time
ago,
in Short Wave Magazine (UK), John Wilson showed the spectrum analyser
display
of a BBC MW broadcast station. It was tightly filtered above 4+ kHz to
stay
with the allowed channel. Many AM stations also process their signals..

I like your idea of having two ceramic filters before the synchronous
detector.
I see that the oscillator in the AD607 has a wide tuning range, and it
would
be very unhelpful if it locked to the 'wrong' signal. As a contrast the
synch
oscillator in the ICF-2010, which is also used as the BFO, can only be
moved a
small frequency eg. 3 kHz (please do not quote me on this - I did measure
it
once) either side of 455kHz.

I must admit that I am still intrigued by the idea in Brook's article of
having
using the sync. oscillator as a BFO and restricting it to a very narrow
(+/-
20Hz ?) locking range. One could then listen normally with envelope
detection,
turn on the BFO to get ECSS detection, and then once one has obtained a
zero
beat, turn it to sync mode. However it is not something which I would
wish to
put into a general purpose radio.

Let me register my interest in seeing the AD application note on your web
site.
If you want a copy of the Brook article, please contact me off list.

73 John KC0GGH