Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

regards,
NEO

N9NEO wrote:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

regards,
NEO

AGC systems don't lend themselves to easy modification.

There are many issues, attack time and release time, are the two most
significant.

Too fast the audio gets "chopy", too slow not enough effect.

I think I can say that I really understand the Kenwood R2000. And while
I have
tried several "improved" AGC designs, none made enough difference to be
worth mentioning.

The DX398 has some published modifications that you may want to track
down.
The main effect as I recall was to slow the release time. The DX398's
AGC
is a tad too fast.

Good luck and let us know how it works.

Synch detectors can mitigate the some of the effects caused by fading.
But in my experience are not the "do all- end all" that I had hoped.

At this point I have decided to concentrate on improving my antenna
to get the most signal and as little noise as possible. A much better
pay off for the energy required.

Terry

"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

Synchronous detectors have never been about dealing with fading. They
are about ensuring there is enough "carrier" to beat the sidebands down
to audio.

So there's fading on the incoming signal. That means the amplitude of
the sidebands is varying with that fading. A locally generated "carrier"
at the receiver ensures that there is something to beat those sidebands
down to audio, even if the transmitter's carrier has faded too much to
do the proper job. But a constant level "carrier" at the receiver beats
the sideband down to audio intact, ie an ideal mixer would not add anything
to the signal. So if the sideband is fading, of course the audio output
of the receiver will vary with that fading.

What the sync detector brings you is the ability to decode that signal
even if the carrier goes missing, because of selective fading.

Dealing with the fading of the sidebands is in a different realm, and
obviously a miraculous receiver that eliminates fading has long been
sought after. Armstrong dealt with it in part, by moving to FM
and using limiters in the receiver, but that only works when the signal
is above a certain level. Below it, the signal levels are too low for
the limiters to kick in, and that fading is obvious.

Beyond a certain point, you get conflict. Have a scheme that does
a really good job of eliminating the fading, and likely that starts
affecting the "fidelity" of the signal, because how do you discriminate
between the voice at the transmitter end varying in amplitude, because
the speaker starts talking more quietly or even just because sounds are
made up of varying levels, and the signal fading as it travels to the
receiver? It's easy to counter some of the fading, but it gets harder
the more you try to conquer it.

Michael

In article ,
(Michael Black) wrote:

"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

Synchronous detectors have never been about dealing with fading. They
are about ensuring there is enough "carrier" to beat the sidebands down
to audio.

Snip

Sync is for selective fading specifically when the carrier fades but
most of the side band information is still there. When the fading is
wide and covers the entire channel it can not help.

--
Telamon
Ventura, California

The purpose of the sync detector is not to reduce fading, but to reduce the
distortion during the fades. A good sync detector does a remarkable job of
that, even when listening to music. A sync detector that allows one side
band to be selected adds the ability to reduce adjacent channel inteference.

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

wrote in message
oups.com...

N9NEO wrote:

Synch detectors can mitigate the some of the effects caused by fading.
But in my experience are not the "do all- end all" that I had hoped.

Terry

Michael Black wrote:
Beyond a certain point, you get conflict. Have a scheme that does
a really good job of eliminating the fading, and likely that starts
affecting the "fidelity" of the signal, because how do you discriminate
between the voice at the transmitter end varying in amplitude, because
the speaker starts talking more quietly or even just because sounds are
made up of varying levels, and the signal fading as it travels to the
receiver? It's easy to counter some of the fading, but it gets harder
the more you try to conquer it.

Michael
Has anyone tried to measure the fading of the carrier and use that as a
guide as to whether the level change in the sideband is fading related
or program content related?

Bob

Michael Black wrote:
"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

Synchronous detectors have never been about dealing with fading. They
are about ensuring there is enough "carrier" to beat the sidebands down
to audio.

Narrow band signal have less fading, thus sync demod will have less
fading. However, the result isn't all that significant since all you
have done is cut the bandwidth in half.


So there's fading on the incoming signal. That means the amplitude of
the sidebands is varying with that fading. A locally generated "carrier"
at the receiver ensures that there is something to beat those sidebands
down to audio, even if the transmitter's carrier has faded too much to
do the proper job. But a constant level "carrier" at the receiver beats
the sideband down to audio intact, ie an ideal mixer would not add anything
to the signal. So if the sideband is fading, of course the audio output
of the receiver will vary with that fading.

With an envelope detector, the carrier isn't beating down the sideband.
If you just look at the math of AM modulation, you would see that the
carrier is just there for the ride.

What the sync detector brings you is the ability to decode that signal
even if the carrier goes missing, because of selective fading.

Dealing with the fading of the sidebands is in a different realm, and
obviously a miraculous receiver that eliminates fading has long been
sought after. Armstrong dealt with it in part, by moving to FM
and using limiters in the receiver, but that only works when the signal
is above a certain level. Below it, the signal levels are too low for
the limiters to kick in, and that fading is obvious.

Beyond a certain point, you get conflict. Have a scheme that does
a really good job of eliminating the fading, and likely that starts
affecting the "fidelity" of the signal, because how do you discriminate
between the voice at the transmitter end varying in amplitude, because
the speaker starts talking more quietly or even just because sounds are
made up of varying levels, and the signal fading as it travels to the
receiver? It's easy to counter some of the fading, but it gets harder
the more you try to conquer it.

Michael

Telamon wrote:
In article ,
(Michael Black) wrote:

"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

Synchronous detectors have never been about dealing with fading. They
are about ensuring there is enough "carrier" to beat the sidebands down
to audio.

Snip

Sync is for selective fading specifically when the carrier fades but
most of the side band information is still there. When the fading is
wide and covers the entire channel it can not help.

--
Telamon
Ventura, California

With analog tuners, does tunig off the main carrier, a bit, get one
into the sidebands, and if so, are there any advantages to analog
tuners ?

Thanks

In article . com,
wrote:

Michael Black wrote:
"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio.
The sync detector seems to take care of a lot of the distortion,
but the audio continues fading in and out and is quite annoying.
Could the fading be mitigated to any extent by using another
stage of agc? I am going to be doing some experiments with the
455kc if out on my Red Sun RP2100 whenever it gets here.
Detectors, filters, SSB, etc... I thought that along with other
experiments I might want to try some outboard agc.

Synchronous detectors have never been about dealing with fading.
They are about ensuring there is enough "carrier" to beat the
sidebands down to audio.

Narrow band signal have less fading, thus sync demod will have less
fading. However, the result isn't all that significant since all you
have done is cut the bandwidth in half.

Narrow band signals do not have less fading.

So there's fading on the incoming signal. That means the amplitude
of the sidebands is varying with that fading. A locally generated
"carrier" at the receiver ensures that there is something to beat
those sidebands down to audio, even if the transmitter's carrier
has faded too much to do the proper job. But a constant level
"carrier" at the receiver beats the sideband down to audio intact,
ie an ideal mixer would not add anything to the signal. So if the
sideband is fading, of course the audio output of the receiver will
vary with that fading.

With an envelope detector, the carrier isn't beating down the
sideband. If you just look at the math of AM modulation, you would
see that the carrier is just there for the ride.

Selective fading occurs when conditions cause a very narrow band of
frequencies to be received at very low amplitudes where most of the
side band information is present at levels that your receiver can
ordinarily demodulate properly.

When part of the side band is being notched out it does not sound all
that bad but when the carrier gets weakened then the AM demodulator
can't process the side band information properly and there is
horrendous distortion. The carrier which is at the right frequency and
phase relative to the side band information keeps the detector in the
linear region so distortion is minimized.

A sync detector uses a local oscillator in a similar to the way SSB is
detected with the difference that it is phase locked to the signal
carrier and mixed with it so when the carrier fades out this near
perfect copy of the carrier allows the demodulator to continue to
detect the side band or bands without distortion during a carrier
fading condition. Here this necessary frequency and phase information
carried by the "carrier" is retained by the sync circuitry.

What the sync detector brings you is the ability to decode that
signal even if the carrier goes missing, because of selective
fading.


Snip

Michael has it right.

--
Telamon
Ventura, California

wrote:


Michael Black wrote:
"N9NEO" ) writes:
Greetings,

I have just got a sony ICF sw7600GR and it is a very nice radio. The
sync detector seems to take care of a lot of the distortion, but the
audio continues fading in and out and is quite annoying. Could the
fading be mitigated to any extent by using another stage of agc? I am
going to be doing some experiments with the 455kc if out on my Red Sun
RP2100 whenever it gets here. Detectors, filters, SSB, etc... I thought
that along with other experiments I might want to try some outboard
agc.

Synchronous detectors have never been about dealing with fading. They
are about ensuring there is enough "carrier" to beat the sidebands down
to audio.

Narrow band signal have less fading, thus sync demod will have less
fading. However, the result isn't all that significant since all you
have done is cut the bandwidth in half.


So there's fading on the incoming signal. That means the amplitude of
the sidebands is varying with that fading. A locally generated "carrier"
at the receiver ensures that there is something to beat those sidebands
down to audio, even if the transmitter's carrier has faded too much to
do the proper job. But a constant level "carrier" at the receiver beats
the sideband down to audio intact, ie an ideal mixer would not add
anything
to the signal. So if the sideband is fading, of course the audio output
of the receiver will vary with that fading.

With an envelope detector, the carrier isn't beating down the sideband.
If you just look at the math of AM modulation, you would see that the
carrier is just there for the ride.

If you look closely at the operation of an envelope detector, you find the
carrier is an important component.


What the sync detector brings you is the ability to decode that signal
even if the carrier goes missing, because of selective fading.

Dealing with the fading of the sidebands is in a different realm, and
obviously a miraculous receiver that eliminates fading has long been
sought after. Armstrong dealt with it in part, by moving to FM
and using limiters in the receiver, but that only works when the signal
is above a certain level. Below it, the signal levels are too low for
the limiters to kick in, and that fading is obvious.

Beyond a certain point, you get conflict. Have a scheme that does
a really good job of eliminating the fading, and likely that starts
affecting the "fidelity" of the signal, because how do you discriminate
between the voice at the transmitter end varying in amplitude, because
the speaker starts talking more quietly or even just because sounds are
made up of varying levels, and the signal fading as it travels to the
receiver? It's easy to counter some of the fading, but it gets harder
the more you try to conquer it.

Michael