Just wondering, as no one explains what it does or how it works.

"atomicthumbs" ) writes:
Just wondering, as no one explains what it does or how it works.

An AM signal has a carrier and two sidebands. The sidebands carry the
actual content (and they are identical, meaning only one is necessary)
while the carrier just goes along for the ride. But at the receiver end,
the carrier is needed to beat with the sidebands to translate the
modulation from RF back down to audio. (Imagine a 10MHz signal, with a 1KHz
tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz,
plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz
carrier at the receiver and you get the 1KHz signal out of the speaker again.)

Due to propagation, there are times when the carrier can fade more than the
sidebands, so it's too weak to properly demodulate the signal. You end up
with a distorted signal.

Synchronous detection uses a locally generated signal in the receiver to beat
against the sidebands to translate them back to audio. Since this local
"carrier" is nice and strong, it can never be too weak in reference to the
incoming sidebands. The signal may be weak, but it won't be distorted.

The problem, though, is that this local "carrier" has to be right at
the spot halfway between the sidebands. An obvious reason is that if
it's mistuned, you will hear a beat note between the signal's carrier
and the local "carrier". A constant and obnoxious tone in your ear.

But more important, if that local "carrier" is not right in the middle,
the sidebands will not translate to the same audio frequency. WIth
that previous example, both the upper (10.001KHz ) and the lower (9.999KHz)
sidebands both translate to 1KHz because the carrier is right in the middle.
But if this locally generated "carrier" is not right in the middle,
one sideband would translate to 1.1KHz and 990Hz, for example. You've
not only got them translated to the wrong frequency, but you suddenly have
two frequencies instead of one at audio. It will sound horrible.

This is where the "synch" comes in. There is circuitry in the receiver
to lock this local "carrier" to the incoming signal. The incoming signal
includes enough information so that exact middle point between the sidebands
can be determined, and this synchronization ensures that this local
"carrier" is set to that frequency.

The sidebands translate to the correct audio frequency, and everything
is well.

If there is no lock of this local "carrier" then the modulating signals
do not translate to the correct audio frequencies.

And as a side issue, once you have this circuitry in place, it doesn't
take all that much more to allow selectable sideband. Since both
sidebands carry identical information, only one is needed to recover
the modulation. With the right circuitry, the receiver can select which
of these redundant sidebands are used, so if one has some interference,
the other one may not and selecting that one will mean the listener
will not hear the interference.

Michael

Wow, excellent description, thanks.

Mark.
Auckland
New Zealand.

"Michael Black" wrote in message
...

"atomicthumbs" ) writes:
Just wondering, as no one explains what it does or how it works.

An AM signal has a carrier and two sidebands. The sidebands carry the
actual content (and they are identical, meaning only one is necessary)
while the carrier just goes along for the ride. But at the receiver end,
the carrier is needed to beat with the sidebands to translate the
modulation from RF back down to audio. (Imagine a 10MHz signal, with a
1KHz
tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz,
plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz
carrier at the receiver and you get the 1KHz signal out of the speaker
again.)

Due to propagation, there are times when the carrier can fade more than
the
sidebands, so it's too weak to properly demodulate the signal. You end up
with a distorted signal.

Synchronous detection uses a locally generated signal in the receiver to
beat
against the sidebands to translate them back to audio. Since this local
"carrier" is nice and strong, it can never be too weak in reference to the
incoming sidebands. The signal may be weak, but it won't be distorted.

The problem, though, is that this local "carrier" has to be right at
the spot halfway between the sidebands. An obvious reason is that if
it's mistuned, you will hear a beat note between the signal's carrier
and the local "carrier". A constant and obnoxious tone in your ear.

But more important, if that local "carrier" is not right in the middle,
the sidebands will not translate to the same audio frequency. WIth
that previous example, both the upper (10.001KHz ) and the lower
(9.999KHz)
sidebands both translate to 1KHz because the carrier is right in the
middle.
But if this locally generated "carrier" is not right in the middle,
one sideband would translate to 1.1KHz and 990Hz, for example. You've
not only got them translated to the wrong frequency, but you suddenly have
two frequencies instead of one at audio. It will sound horrible.

This is where the "synch" comes in. There is circuitry in the receiver
to lock this local "carrier" to the incoming signal. The incoming signal
includes enough information so that exact middle point between the
sidebands
can be determined, and this synchronization ensures that this local
"carrier" is set to that frequency.

The sidebands translate to the correct audio frequency, and everything
is well.

If there is no lock of this local "carrier" then the modulating signals
do not translate to the correct audio frequencies.

And as a side issue, once you have this circuitry in place, it doesn't
take all that much more to allow selectable sideband. Since both
sidebands carry identical information, only one is needed to recover
the modulation. With the right circuitry, the receiver can select which
of these redundant sidebands are used, so if one has some interference,
the other one may not and selecting that one will mean the listener
will not hear the interference.

Michael

"Michael Black" wrote in message
...

"atomicthumbs" ) writes:
Just wondering, as no one explains what it does or how it works.

An AM signal has a carrier and two sidebands. The sidebands carry the
actual content (and they are identical, meaning only one is necessary)
while the carrier just goes along for the ride. But at the receiver end,
the carrier is needed to beat with the sidebands to translate the
modulation from RF back down to audio. (Imagine a 10MHz signal, with a
1KHz
tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz,
plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz
carrier at the receiver and you get the 1KHz signal out of the speaker
again.)

Due to propagation, there are times when the carrier can fade more than
the
sidebands, so it's too weak to properly demodulate the signal. You end up
with a distorted signal.

Synchronous detection uses a locally generated signal in the receiver to
beat
against the sidebands to translate them back to audio. Since this local
"carrier" is nice and strong, it can never be too weak in reference to the
incoming sidebands. The signal may be weak, but it won't be distorted.

The problem, though, is that this local "carrier" has to be right at
the spot halfway between the sidebands. An obvious reason is that if
it's mistuned, you will hear a beat note between the signal's carrier
and the local "carrier". A constant and obnoxious tone in your ear.

But more important, if that local "carrier" is not right in the middle,
the sidebands will not translate to the same audio frequency. WIth
that previous example, both the upper (10.001KHz ) and the lower
(9.999KHz)
sidebands both translate to 1KHz because the carrier is right in the
middle.
But if this locally generated "carrier" is not right in the middle,
one sideband would translate to 1.1KHz and 990Hz, for example. You've
not only got them translated to the wrong frequency, but you suddenly have
two frequencies instead of one at audio. It will sound horrible.

This is where the "synch" comes in. There is circuitry in the receiver
to lock this local "carrier" to the incoming signal. The incoming signal
includes enough information so that exact middle point between the
sidebands
can be determined, and this synchronization ensures that this local
"carrier" is set to that frequency.

The sidebands translate to the correct audio frequency, and everything
is well.

If there is no lock of this local "carrier" then the modulating signals
do not translate to the correct audio frequencies.

And as a side issue, once you have this circuitry in place, it doesn't
take all that much more to allow selectable sideband. Since both
sidebands carry identical information, only one is needed to recover
the modulation. With the right circuitry, the receiver can select which
of these redundant sidebands are used, so if one has some interference,
the other one may not and selecting that one will mean the listener
will not hear the interference.

Michael



Then,

why do they have double sideband on some rigs like the Lowe HF-150? What
purpose does double sideband serve and what is it's benefits?

Stronger lock??

Lucky

Lucky wrote:

"Michael Black" wrote in message
...

"atomicthumbs" ) writes:
Just wondering, as no one explains what it does or how it works.

An AM signal has a carrier and two sidebands. The sidebands carry the
actual content (and they are identical, meaning only one is necessary)
while the carrier just goes along for the ride. But at the receiver end,
the carrier is needed to beat with the sidebands to translate the
modulation from RF back down to audio. (Imagine a 10MHz signal, with a
1KHz
tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz,
plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz
carrier at the receiver and you get the 1KHz signal out of the speaker
again.)

Due to propagation, there are times when the carrier can fade more than
the
sidebands, so it's too weak to properly demodulate the signal. You end up
with a distorted signal.

Synchronous detection uses a locally generated signal in the receiver to
beat
against the sidebands to translate them back to audio. Since this local
"carrier" is nice and strong, it can never be too weak in reference to the
incoming sidebands. The signal may be weak, but it won't be distorted.

The problem, though, is that this local "carrier" has to be right at
the spot halfway between the sidebands. An obvious reason is that if
it's mistuned, you will hear a beat note between the signal's carrier
and the local "carrier". A constant and obnoxious tone in your ear.

But more important, if that local "carrier" is not right in the middle,
the sidebands will not translate to the same audio frequency. WIth
that previous example, both the upper (10.001KHz ) and the lower
(9.999KHz)
sidebands both translate to 1KHz because the carrier is right in the
middle.
But if this locally generated "carrier" is not right in the middle,
one sideband would translate to 1.1KHz and 990Hz, for example. You've
not only got them translated to the wrong frequency, but you suddenly have
two frequencies instead of one at audio. It will sound horrible.

This is where the "synch" comes in. There is circuitry in the receiver
to lock this local "carrier" to the incoming signal. The incoming signal
includes enough information so that exact middle point between the
sidebands
can be determined, and this synchronization ensures that this local
"carrier" is set to that frequency.

The sidebands translate to the correct audio frequency, and everything
is well.

If there is no lock of this local "carrier" then the modulating signals
do not translate to the correct audio frequencies.

And as a side issue, once you have this circuitry in place, it doesn't
take all that much more to allow selectable sideband. Since both
sidebands carry identical information, only one is needed to recover
the modulation. With the right circuitry, the receiver can select which
of these redundant sidebands are used, so if one has some interference,
the other one may not and selecting that one will mean the listener
will not hear the interference.

Michael



Then,

why do they have double sideband on some rigs like the Lowe HF-150? What
purpose does double sideband serve and what is it's benefits?

No real benefit compared to sideband selectable sync, other than the fact that
you have sync. Take for example the R8 and R8A, they both have sync on both
sidebands at once, compared to the better sideband selectable sync on the R8B.

dxAce
Michigan
USA

Thanx!

"atomicthumbs" wrote in
oups.com:

Due to people's obsession to possess things that have certain terms
affiliated with them (Namely, in this case, Synchronous Detection), allow
me to direct you to the following link.

Concerning the venerable Icom R-75 with "Synchronous Detection", Radio
Netherlands had the following to say:

"Spot the Difference with the Sync

What is the singular failing of this receiver? In our opinion, there is
virtually no difference between synchronous AM and AM reception. The
synchronous mode includes both sidebands; there is no option to choose
the lower or upper sideband. The Lowe HF-150 synchronous modes and
performance are far superior. We urge that ICOM correct the synchronous
performance in future models and make available a retrofit ROM available
to current customers.

Fortunately all is not lost here. As the receiver's SSB reception is
quite good, in difficult or crowded band conditions, we simply tune in
the appropriate sideband of the desired signal and, if necessary, adjust
the PBT controls."

http://www2.rnw.nl/rnw/en/features/m...ceivers/icr75b.
html

As I have diatribed before, using the SSB capabilities of "quality
receivers and transceivers" functions similarly to using "Synchronous
Detection", or at least the uninformed reviewers at Radio Netherlands
seem to think.

Yes, you can survive without "Synchronous Detection". Using the Icom R-75
and the Yaesu FRG-100, I do not see any differences worthy of lavishing
attention on the Sync features of the Icom.

I will say that in terms of portables, the Sony 7600GR, with the Sync
Detection (when the signal levels are sufficient to preclude the ghastly
noise that the Sony makes as the Sync Detector locks and losses its
lock), is a laudable feature making listening under "some circumstances"
much more enjoyable. (avoiding the noise associated with one sideband or
the other sometimes provides relief, but it seems that not infrequently
the noise the infests one sideband sooner or later manages to infest the
other).

Oddly enough, in terms of 3.210 and 5.070 MHz, my DX-396 is more
sensitive than the Sony, (this is with the antenna extended on the Sony
and the antenna collapsed on the DX-396, using it's internal antenna).

Of course, since Sony makes the worlds best everything (Remember the
obsession to possess things with specific names from the beginning of
this post), it must mean that my Sony is defective.

Soliloquy.

(P.S. to any poster unlucky enough to not have added me to their plonk
files, I have filtered this post, please offer all the antagonism that
you wish, I won't be here to read it ;-)




Just wondering, as no one explains what it does or how it works.

In article ,
"Dr. Artaud" wrote:

Snip

(P.S. to any poster unlucky enough to not have added me to their plonk
files, I have filtered this post, please offer all the antagonism that
you wish, I won't be here to read it ;-)


No problem Dr.

Plonk

--
Telamon
Ventura, California

dxAce wrote:


No real benefit compared to sideband selectable sync, other than the
fact that you have sync. Take for example the R8 and R8A, they both
have sync on both sidebands at once, compared to the better sideband
selectable sync on the R8B.

Drake advertises the R8 and R8A as having 'sideband selectable sync' but you
have to use the passband offset to select one side or the other. Certainly
not as good as the R8B detector. Interestingly the RX-350 (and some other
receivers) give you the choice of both sides, lsb or usb. I guess if there
is no adjacent interference, the 'both' choice is OK but I still don't see
what the benefit is over a choosing the sync with one sideband.

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

wrote:

Others have told me about how sync detection is so dispensible, but my
own ears say otherwise. So who am I supposed to believe....the
aforementioned people or my own ears?

In this day and age, I personally wouldn't buy a new receiver that
lacked sync detection.

I'd still take a nice Drake R7 that does not have sync any old day... I'd out dx
you in most any situation!

dxAce
Michigan
USA