I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

There are some helpful hints here, though I'm puzzled by the gripe this
fellow has with synchronous detection. I personally wouldn't spend a
lot of dough on any receiver that lacked it. I think a lot of people
are sour on synchronous detection because they've bought and/or used a
receiver that had a very poor implementation of it. When sync detection
is done right, as it is on Drake's R8B, then it will sometimes do more
to aid reception than all of these hints put together. But the good
news is that we don't have to choose between synchronous detection and
this fellow's helpful hints. We can have all of these tools at our
disposal.

Steve

Steve wrote:
wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

There are some helpful hints here, though I'm puzzled by the gripe this
fellow has with synchronous detection. I personally wouldn't spend a
lot of dough on any receiver that lacked it. I think a lot of people
are sour on synchronous detection because they've bought and/or used a
receiver that had a very poor implementation of it. When sync detection
is done right, as it is on Drake's R8B, then it will sometimes do more
to aid reception than all of these hints put together. But the good
news is that we don't have to choose between synchronous detection and
this fellow's helpful hints. We can have all of these tools at our
disposal.

Steve

My first expousre to SAM was with an AOR7030+. My first impression was
that
"great". That lead me down a long path toward building my own SAM+
outboard
detector. Along the way I had a chance to test a Kiwa, MAOP and the
Sherwood
SE-3. Both are good and both are much better then the AOR. I tried
several
designs and settled on a variation of Pete's AD607 SAM. Again at first
I was very impressed. However after using it for several months the
glammor started to dull.
For better then 99% of my AM listening, which in truth is a very small
part of my
SWL activity as I am into utility, I ofund the 3 OpAmp simple "improved
detector"
to be the equal or the match for any of the SAMs I had on hand. I was
not able
to compare the MAP or SE-3 for any extened period and while both are
great units,
they do have differences. On balance I like the sound quality of the
MAP over the SE3,
but I liked teh SE3's ability to track rapid, deep fades, espcially
with nearby AM
signals. I had my feet held to the fire for my posts about Dallas
Lankfords
observations about the utility of a sharp LP audio filter that chops
every thing above
~3 or 4KHz. Exact break point depends on individual choice.

Now that I have a R8B, I must admit that this is the best implentation
of a SAM
I have yet experienced. However in many situations it too can benefit
from the
AF LP filter.

Perhaps I expected too much from SAM detectors. They aren't magic and
are far
from perfect. The
home.worldnet.att.net/~wa1sov/technical/sync_det.html
page is no longer up, but Peter C. McNulty, WA1SOV, offered an
additional
OpAmp fitler design that was reported to allow the AD607 to fully
reject
unwanted signals via I and Q difference and summing. I don;t have my
printed
copy in front of me so I can't relate the math. The design appeard to
be valid,
and several other EEs agreed with his reasoning. However I was never
able to
get that part of the design to work. I wrote if off in part to the 50Hz
minimum
tuning step the R2000 offers. His design is clearly worthy of study and
I suspect
that for someone with more time it could be a winner.

At this point I am most interested in reducing the local RF noise,
improving my
antennas and getting to understand how to get the most from my phaser.
Oh,
and I am still after the Holly Grail" of a perfect 12V audio amp.

Terry

wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

Eh, the author confuses DSB and AM. I wouldn't put much faith in
his/her analysis.

On Thu, 30 Nov 2006 20:59:40 GMT, Bart Bailey wrote:

In ups.com
posted on 30 Nov 2006 06:06:29 -0800, Steve wrote: Begin


wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

There are some helpful hints here, though I'm puzzled by the gripe this
fellow has with synchronous detection. I personally wouldn't spend a
lot of dough on any receiver that lacked it. I think a lot of people
are sour on synchronous detection because they've bought and/or used a
receiver that had a very poor implementation of it. When sync detection
is done right, as it is on Drake's R8B, then it will sometimes do more
to aid reception than all of these hints put together. But the good
news is that we don't have to choose between synchronous detection and
this fellow's helpful hints. We can have all of these tools at our
disposal.

Steve

At least the guy gave a thumbs up to the Drake designed SAM in the E1,
although it wasn't referred to in his comments about pass band tuning.
I use both when conditions are rough, as is sometimes the case with KGO
(810) at night, the narrowest 2.3kc IF bandwidth filter combined with a
PBT shift of +1.2kc and a USB sync, which allows complete rejection of
the local XESPN (800) and shifts the audio to a more balanced sound.
The use of wider bandwidth IF filters work fine with SAM on easy
conditions like Radio Australia but in a crowd the extra bandwidth tends
to allow more of an AGC reduction from the then included but undesirable
signals. This is especially true if I'm trying to pick off KKOB (770)
from the side of the local powerhouse KFMB (760).
FWIW: Local is San Diego and the target stations are;
KGO (810) - San Francisco CA
KKOB (770) - Albuquerque NM
The other local interference station XESPN (800) is in Tijuana MX

KFMB 760 S9+15

KKOB 770 S9+10

KKOH 780 S9+15

KABC 790 (out of night pattern)

XESPN 800 S9+12

KGO 810 S9+15

All coming in beautifully (except KABC)

R8B PreAmp Off 50' Random Wire

Lang Station, CA

) writes:
wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

Eh, the author confuses DSB and AM. I wouldn't put much faith in
his/her analysis.

Huh? IN what way?

I glanced at it and maybe missed something, but DSB is AM. And
he certainly says it at the outset, and when he's talking about the
components he's talking about 2 sidebands and a carrier.

Now, "DSB" often has fallen into the meaning of "DSB with no carrier",
but technically one should specifically define that there is no carrier.

Some of the problem with AM reception discussion is that it was defined in
a certain set of terms, for decades and then even for beginners up
till recent times (and maybe even today). So they'd define AM as
a signal that is amplitude modulated, and that sets things up for
the vision that the carrier amplitude goes up and down. Then when
SSB became commonplace, instead of going back from the beginning
and redefining it all, a separate set of definitions gets tacked on.

This leaves people thinking they AM and SSB are two different things,
when they are basically the same.

Then when discussion of "low distortion AM detectors" comes along, it
isn't even clear what people are talking about. Because one is not
using a certain type of detector for AM (ie 2 sidebands with a carrier),
and a different type for SSB. The talk of "Amplitude Modulation" invokes
a vision of a detector that is following the voltage variations of the
signal. But that's not the case at all.

The carrier mixes with the sideband in the "envelope detector" and that
beating is what brings the modulation back down to "baseband". It's just
not a good mixer.

Listen to an SSB signal without a carrier or BFO. That's the sound of the
envelope varying according to the modulating signal, and there's no way
to make sense of it without a carrier. No differing loads on the dioded
detector, no precision half wave detector (with the diode in a feedback
loop), no forward biasing of the diode, can ever make up for the lack of
carrier.

The carrier of an AM signal is needed to beat with the sidebands and
get it back to audio. If the carrier fades in comparison with the
sidebands, you start hearing things like that SSB with an "envelope
detector", because the carrier is no longer strong enough to mix the
sidebands down to audio, and the "envelope detector" is actually
following the envelope of the signal.

The basic concept of demodulation is no different whether the signal
is AM (with carrier), DSB (with no carrier) or SSB (with no carrier). They
all need the carrier, or a locally synthesized equivalent, to beat the
sideband(s) down to audio.

If things were spoken of that way from the beginning, then there'd be less
of a leap to the "synchronous detector". No only would a universal set
of concepts be applied to all modes, but the point of a synchronous
modulator would become clear.

A single diode is a lousy mixer. On the other hand, since the carrier
of an AM signal comes in with the sidebands, there's no reason for
having a second and isolated input for that carrier.

But, long ago, people would mess with "exalted carrier reception", which
would be the first step up from those "envelope detectors". They'd turn
on the Q-multiplier, which had a narrow peak but a wide skirt, and that
would boost the incoming carrier in reference to the sidebands, so
there was a stronger carrier feeding into the "mixer".

It seems that only when SSB came along, and there were design reasons
to go to better mixers for the demodulation, that two input mixers started
being used, commonly called "product detectors". There were design reasons
for going to those, but the basic concept of a locally generated carrier
did not require anything more than the single diode "envelope detector".
Indeed, the concept had been there back in the days of regen receivers,
and every superhet that could be used for CW had a BFO that would feed
into the "envelope detector", to give to provide a beat with the incoming
signal. I should point out that when the synchronous detector was described
in CQ magazine in the late fifties, the actual mixers were single diodes.

But once you had product detectors, that opened things up. The notion of
boosting the incoming carrier for better mixing action became more clear.
I've said before, there was an article in QST about an advanced receiver
in the fifties, and it had two parallel IF chains. One wide for voice,
the other narrow for CW. But, it also allowed the output of the narrow
chain to feed the product detector, and there was the "quasi-synchronous
detector" before anyone came up with the name.

For AM (with carrier), you had two choices. You could strip off
the extra sideband and carrier, then the incoming signal was the
same as an SSB signal, and then demodulate it as an SSB signal. This
saw a lot of useage in the sixties, when SSB only ham rigs hit
the market, and yet AM was still common. People needed a means of
demodulating the AM signals, and that worked. While I think it
got discussed in the fifties as a better means of AM demodulation,
nobody in the sixties was talking that way. It was just a means of
demodulating AM signals when there was no means of doing so. (Not
only did the SSB-only receivers have narrow IF filters, but often
there was no way of turning off the BFO, and the product detectors
were a type of mixer that required having that second signal
at the second input; without it, you'd get little or no output
even with an AM signal that brought it's own carrier.)

But if you didn't want to do that, you had to deal with getting
the "locally generated carrier" in the right place. Not just
so it wouldn't beat against the incoming carrier (when it
was strong enough) but if it wasn't placed in the right place,
the sidebands would not be translated back to audio in the same
places. (So if you sent a 1KHz tone, and the "locally generated
carrier" was not right in the middle between those sidebands, one
sideband would translate down so that 1KHz tone was 1010Hz while
the other would translated down to 990Hz, which would obviously
clash with each other.)

That's what the "synchronous" bit is about. It's about putting
the same sort of BFO that you'd use with SSB (which would feed
the same sort of product detector used for SSB), with the addition
of circuitry to synchronize the BFO with the carrier of the incoming
AM Signal.

If the discussion had started with the AM detector as a mixer, then
there'd be little magic about "synchronous detectors". The whole
process is simply about getting the "carrier" strong in reference
to the sidebands, so good mixing happens in the detector. The
"synchronous" bit is only a secondary thing, a need because
you want the locally generated carrier in the right place.

There have always been various means of getting better mixing
action at the demodulator. But the important thing has always
been about doing that.

Michael

Michael Black wrote:
) writes:
wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

Eh, the author confuses DSB and AM. I wouldn't put much faith in
his/her analysis.

Huh? IN what way?

I glanced at it and maybe missed something, but DSB is AM. And
he certainly says it at the outset, and when he's talking about the
components he's talking about 2 sidebands and a carrier.

Now, "DSB" often has fallen into the meaning of "DSB with no carrier",
but technically one should specifically define that there is no carrier.

DSB never has a carrier. There is no such thing as DSB and DSB without
a carrier, just DSB.

Think of a mixer. If the signal are zero mean, you get DSB. If there is
a DC offset on the modulating signal, you get AM.


Some of the problem with AM reception discussion is that it was defined in
a certain set of terms, for decades and then even for beginners up
till recent times (and maybe even today). So they'd define AM as
a signal that is amplitude modulated, and that sets things up for
the vision that the carrier amplitude goes up and down. Then when
SSB became commonplace, instead of going back from the beginning
and redefining it all, a separate set of definitions gets tacked on.

This leaves people thinking they AM and SSB are two different things,
when they are basically the same.

No, AM and SSB are different.


Then when discussion of "low distortion AM detectors" comes along, it
isn't even clear what people are talking about. Because one is not
using a certain type of detector for AM (ie 2 sidebands with a carrier),
and a different type for SSB. The talk of "Amplitude Modulation" invokes
a vision of a detector that is following the voltage variations of the
signal. But that's not the case at all.

The carrier mixes with the sideband in the "envelope detector" and that
beating is what brings the modulation back down to "baseband". It's just
not a good mixer.

Listen to an SSB signal without a carrier or BFO. That's the sound of the
envelope varying according to the modulating signal, and there's no way
to make sense of it without a carrier. No differing loads on the dioded
detector, no precision half wave detector (with the diode in a feedback
loop), no forward biasing of the diode, can ever make up for the lack of
carrier.

And when did I comment about SSB?


The carrier of an AM signal is needed to beat with the sidebands and
get it back to audio. If the carrier fades in comparison with the
sidebands, you start hearing things like that SSB with an "envelope
detector", because the carrier is no longer strong enough to mix the
sidebands down to audio, and the "envelope detector" is actually
following the envelope of the signal.

The basic concept of demodulation is no different whether the signal
is AM (with carrier), DSB (with no carrier) or SSB (with no carrier). They
all need the carrier, or a locally synthesized equivalent, to beat the
sideband(s) down to audio.

If things were spoken of that way from the beginning, then there'd be less
of a leap to the "synchronous detector". No only would a universal set
of concepts be applied to all modes, but the point of a synchronous
modulator would become clear.

A single diode is a lousy mixer. On the other hand, since the carrier
of an AM signal comes in with the sidebands, there's no reason for
having a second and isolated input for that carrier.

But, long ago, people would mess with "exalted carrier reception", which
would be the first step up from those "envelope detectors". They'd turn
on the Q-multiplier, which had a narrow peak but a wide skirt, and that
would boost the incoming carrier in reference to the sidebands, so
there was a stronger carrier feeding into the "mixer".

It seems that only when SSB came along, and there were design reasons
to go to better mixers for the demodulation, that two input mixers started
being used, commonly called "product detectors". There were design reasons
for going to those, but the basic concept of a locally generated carrier
did not require anything more than the single diode "envelope detector".
Indeed, the concept had been there back in the days of regen receivers,
and every superhet that could be used for CW had a BFO that would feed
into the "envelope detector", to give to provide a beat with the incoming
signal. I should point out that when the synchronous detector was described
in CQ magazine in the late fifties, the actual mixers were single diodes.

But once you had product detectors, that opened things up. The notion of
boosting the incoming carrier for better mixing action became more clear.
I've said before, there was an article in QST about an advanced receiver
in the fifties, and it had two parallel IF chains. One wide for voice,
the other narrow for CW. But, it also allowed the output of the narrow
chain to feed the product detector, and there was the "quasi-synchronous
detector" before anyone came up with the name.

For AM (with carrier), you had two choices. You could strip off
the extra sideband and carrier, then the incoming signal was the
same as an SSB signal, and then demodulate it as an SSB signal. This
saw a lot of useage in the sixties, when SSB only ham rigs hit
the market, and yet AM was still common. People needed a means of
demodulating the AM signals, and that worked. While I think it
got discussed in the fifties as a better means of AM demodulation,
nobody in the sixties was talking that way. It was just a means of
demodulating AM signals when there was no means of doing so. (Not
only did the SSB-only receivers have narrow IF filters, but often
there was no way of turning off the BFO, and the product detectors
were a type of mixer that required having that second signal
at the second input; without it, you'd get little or no output
even with an AM signal that brought it's own carrier.)

But if you didn't want to do that, you had to deal with getting
the "locally generated carrier" in the right place. Not just
so it wouldn't beat against the incoming carrier (when it
was strong enough) but if it wasn't placed in the right place,
the sidebands would not be translated back to audio in the same
places. (So if you sent a 1KHz tone, and the "locally generated
carrier" was not right in the middle between those sidebands, one
sideband would translate down so that 1KHz tone was 1010Hz while
the other would translated down to 990Hz, which would obviously
clash with each other.)

That's what the "synchronous" bit is about. It's about putting
the same sort of BFO that you'd use with SSB (which would feed
the same sort of product detector used for SSB), with the addition
of circuitry to synchronize the BFO with the carrier of the incoming
AM Signal.

If the discussion had started with the AM detector as a mixer, then
there'd be little magic about "synchronous detectors". The whole
process is simply about getting the "carrier" strong in reference
to the sidebands, so good mixing happens in the detector. The
"synchronous" bit is only a secondary thing, a need because
you want the locally generated carrier in the right place.

There have always been various means of getting better mixing
action at the demodulator. But the important thing has always
been about doing that.

Michael

Christ all mighty, what is with the verbal diarrhea? You are trying to
analyze modulation by looking at demodulation. This is wrong thinking.
You analyze modulation by looking at modulators.

AM:
One mixer. Feed it a carrier and signal. The carrier is zero mean. The
signal has a DC bias sufficient that the signal always remains
positive. Congrats, you gave birth to AM.
DSB:
One mixer: Feed it zero mean carrier and signal. Out pops DSB.
SSB:
Slightly more complicated since it involves Hilbert transformers and
quadrature mixers. I can do an explanation, but it might take a
paragraph.

My original comment still stands. The author of the paper confused AM
and DSB.

In article .com,
"Steve" wrote:

wrote:
I found this web page while looking for a nifty audio filter I
found last year. At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

There are some helpful hints here, though I'm puzzled by the gripe
this fellow has with synchronous detection. I personally wouldn't
spend a lot of dough on any receiver that lacked it. I think a lot of
people are sour on synchronous detection because they've bought
and/or used a receiver that had a very poor implementation of it.
When sync detection is done right, as it is on Drake's R8B, then it
will sometimes do more to aid reception than all of these hints put
together. But the good news is that we don't have to choose between
synchronous detection and this fellow's helpful hints. We can have
all of these tools at our disposal.

Some of it is regional reception patterns, ax grinding, ignorance, and
some of it is just plain nut case thinking focusing on the negative
aspects because the sync circuit in radios are not perfect and ignoring
the good performance that results most of the time.

Listening to AMBCB in the car where I don't have a sync detector and
home where I do sure makes me wish I had it in the car. I'm not talking
about some small improvement I'm talking huge. Without sync you can
have a strong but completely unintelligible signal for a few seconds to
a few minutes a lot of the time in the evenings on any station not
right in town or more than 50 miles away or in other words most
stations. Usually the distortion is more like a few seconds length on
SW but whether you miss a few words or miss whole paragraphs of the
conversation it is very annoying.

It depends on conditions of course but when you have selective fading
turning on the sync detector makes an absolutely huge difference in
reception even with the Sony 7600 portable.

And of course if you have side band selectable sync detection with
another station or local noise source generating interference to one
side of a station you want to receive usually results in near 100%
rejection of the offender by selecting the opposite side band. It's as
close to a magic improvement in reception you are going to get on a
radio. Again this results in a huge non-arguable difference in
reception quality.

The improvement in reception most radios have with sync detection is
huge not small and so the improvement is not open to argument. People
that argue about it are being stupid. People can write anything on
Usenet or on a web page and a lot of it is crapola.

--
Telamon
Ventura, California

In article ,
"Brenda Ann" wrote:

"Michael Black" wrote in message
...
) writes:
wrote:
I found this web page while looking for a nifty audio filter I
found last year. At the very least it gives food for thought.

http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf

Terry

Eh, the author confuses DSB and AM. I wouldn't put much faith in
his/her analysis.

Huh? IN what way?

I glanced at it and maybe missed something, but DSB is AM. And he
certainly says it at the outset, and when he's talking about the
components he's talking about 2 sidebands and a carrier.

Now, "DSB" often has fallen into the meaning of "DSB with no
carrier", but technically one should specifically define that there
is no carrier.

Some of the problem with AM reception discussion is that it was
defined in a certain set of terms, for decades and then even for
beginners up till recent times (and maybe even today). So they'd
define AM as a signal that is amplitude modulated, and that sets
things up for the vision that the carrier amplitude goes up and
down. Then when SSB became commonplace, instead of going back from
the beginning and redefining it all, a separate set of definitions
gets tacked on.

This leaves people thinking they AM and SSB are two different
things, when they are basically the same.

Then when discussion of "low distortion AM detectors" comes along,
it isn't even clear what people are talking about. Because one is
not using a certain type of detector for AM (ie 2 sidebands with a
carrier), and a different type for SSB. The talk of "Amplitude
Modulation" invokes a vision of a detector that is following the
voltage variations of the signal. But that's not the case at all.

The carrier mixes with the sideband in the "envelope detector" and
that beating is what brings the modulation back down to "baseband".
It's just not a good mixer.

Listen to an SSB signal without a carrier or BFO. That's the sound
of the envelope varying according to the modulating signal, and
there's no way to make sense of it without a carrier. No differing
loads on the dioded detector, no precision half wave detector (with
the diode in a feedback loop), no forward biasing of the diode,
can ever make up for the lack of carrier.

The carrier of an AM signal is needed to beat with the sidebands
and get it back to audio. If the carrier fades in comparison with
the sidebands, you start hearing things like that SSB with an
"envelope detector", because the carrier is no longer strong enough
to mix the sidebands down to audio, and the "envelope detector" is
actually following the envelope of the signal.

The basic concept of demodulation is no different whether the
signal is AM (with carrier), DSB (with no carrier) or SSB (with no
carrier). They all need the carrier, or a locally synthesized
equivalent, to beat the sideband(s) down to audio.

If things were spoken of that way from the beginning, then there'd
be less of a leap to the "synchronous detector". No only would a
universal set of concepts be applied to all modes, but the point of
a synchronous modulator would become clear.

A single diode is a lousy mixer. On the other hand, since the
carrier of an AM signal comes in with the sidebands, there's no
reason for having a second and isolated input for that carrier.

But, long ago, people would mess with "exalted carrier reception",
which would be the first step up from those "envelope detectors".
They'd turn on the Q-multiplier, which had a narrow peak but a wide
skirt, and that would boost the incoming carrier in reference to
the sidebands, so there was a stronger carrier feeding into the
"mixer".

It seems that only when SSB came along, and there were design
reasons to go to better mixers for the demodulation, that two input
mixers started being used, commonly called "product detectors".
There were design reasons for going to those, but the basic concept
of a locally generated carrier did not require anything more than
the single diode "envelope detector". Indeed, the concept had been
there back in the days of regen receivers, and every superhet that
could be used for CW had a BFO that would feed into the "envelope
detector", to give to provide a beat with the incoming signal. I
should point out that when the synchronous detector was described
in CQ magazine in the late fifties, the actual mixers were single
diodes.

But once you had product detectors, that opened things up. The
notion of boosting the incoming carrier for better mixing action
became more clear. I've said before, there was an article in QST
about an advanced receiver in the fifties, and it had two parallel
IF chains. One wide for voice, the other narrow for CW. But, it
also allowed the output of the narrow chain to feed the product
detector, and there was the "quasi-synchronous detector" before
anyone came up with the name.

For AM (with carrier), you had two choices. You could strip off
the extra sideband and carrier, then the incoming signal was the
same as an SSB signal, and then demodulate it as an SSB signal.
This saw a lot of useage in the sixties, when SSB only ham rigs hit
the market, and yet AM was still common. People needed a means of
demodulating the AM signals, and that worked. While I think it got
discussed in the fifties as a better means of AM demodulation,
nobody in the sixties was talking that way. It was just a means of
demodulating AM signals when there was no means of doing so. (Not
only did the SSB-only receivers have narrow IF filters, but often
there was no way of turning off the BFO, and the product detectors
were a type of mixer that required having that second signal at the
second input; without it, you'd get little or no output even with
an AM signal that brought it's own carrier.)

But if you didn't want to do that, you had to deal with getting the
"locally generated carrier" in the right place. Not just so it
wouldn't beat against the incoming carrier (when it was strong
enough) but if it wasn't placed in the right place, the sidebands
would not be translated back to audio in the same places. (So if
you sent a 1KHz tone, and the "locally generated carrier" was not
right in the middle between those sidebands, one sideband would
translate down so that 1KHz tone was 1010Hz while the other would
translated down to 990Hz, which would obviously clash with each
other.)

That's what the "synchronous" bit is about. It's about putting the
same sort of BFO that you'd use with SSB (which would feed the same
sort of product detector used for SSB), with the addition of
circuitry to synchronize the BFO with the carrier of the incoming
AM Signal.

If the discussion had started with the AM detector as a mixer, then
there'd be little magic about "synchronous detectors". The whole
process is simply about getting the "carrier" strong in reference
to the sidebands, so good mixing happens in the detector. The
"synchronous" bit is only a secondary thing, a need because you
want the locally generated carrier in the right place.

There have always been various means of getting better mixing
action at the demodulator. But the important thing has always been
about doing that.

Michael

Damn good explanation, Michael. And 100% accurate.

He always writes good posts.

--
Telamon
Ventura, California

On Fri, 01 Dec 2006 08:43:43 GMT, Bart Bailey wrote:




Interesting that KABC (790) isn't heard in your area.
Not as strong as KNX (1070) but definitely good copy here.
What do you hear at 1MHz?
KCEO - Escondido
or KOMO - Seattle
You're between them.
I can only get a co-channel mix here in town but if I go up to Mt
Laguna, about 40 miles east, then the loop separates them nicely. Also
on occasions there's an unknown co-channel MX station under KGO that the
loop can't separate from here. Haven't tried it on the hill yet.

I can hear KABC, plus another station and they fight with each other
and the KABC skywave.

KOMO 1000 is always there, almost like fringe groundwave. I think it
may be ducting along the coast.

There's a ''TIS'' station at UCLA on 810; more of a problem than the
Mexican.