RadioBanter - Grundig 750 or Grundig G3

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Grundig 750 or Grundig G3

Bruce,

My G5 can do SSB but it's via a fine tune knob. Not separate USB/LSB.
I can't really complain about the G5, I think I just want a new toy to
play with.

Now my G6, I can only get in USB signals, it just won't work with
anything on LSB. Weird.

Grundig 750 or Grundig G3

Bob Dobbs wrote:
joe wrote:
Bob Dobbs wrote:
SC Dxing wrote:
Operator Bob,

I guess the questions I am asking. Does having separate USB/LSB switch
make a difference when listening to sideband signals?
Sure does!

Will having
separate USB/LSB along with synch detection make that much of a
difference trying to listen to weak AM signals both on AM and
shortwave?
If your experience matches mine you might have some difficulty getting the
sync-det to lock on the variable intensity SSB signals but on AM it will make a
difference depending on which side of the signal is being encroached.
I guess you mean AMBCB and SW in which case the operation is the same.

A sync detector is not designed to be used on an SSB signal. It is no
wonder that you have some difficulty.

Was just answering the question from the person I responded to,
I know full well how it works but I can see where my answer might be
misconstrued and confusing.

A sync detector works by locking onto the carrier of the signal. In SSB
there is no carrier.

When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.

In SSB there is no carrier at all, you seem to be saying that there is.

The common AM mode (DSB modulation with carrier) has a carrier,
modulated or not. SSB is nothing with no modulation and one sideband
only when there is modulation.

If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.

True as a steady tone is just like a carrier. Because it may look like
one does not mean it is.

note* - there isn't a way to engage the sync-det in either of the SSB modes on
the only radio I have that has it.

Of course not, it would make no sense.

However, if your radio has USB/LSB selectable sync modes, then the only
difference between that and SSB is the injected carrier to the product
detector is either phase locked, or not.

Grundig 750 or Grundig G3

Bob Dobbs wrote:
When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.
If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.
note* - there isn't a way to engage the sync-det in either of the SSB modes on
the only radio I have that has it.

No. Most ham rigs made since 1980 don't actually produce an AM signal, they
produce a double sideband reduced carrier signal. Ham rigs produce a signal
by taking an AM signal and running it through a filter to remove
the carrier and the other sideband.

Their "AM" mode signal is made by recombining the the upper and lower sideband
signals, with only a tiny residual carrier.

Most AM receivers can receive this signal, but there is no carrier to lock
on to, so I doubt that a sync detector can lock onto them.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.

Grundig 750 or Grundig G3

On Thu, 1 Apr 2010, Geoffrey S. Mendelson wrote:

Bob Dobbs wrote:
When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.
If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.
note* - there isn't a way to engage the sync-det in either of the SSB modes on
the only radio I have that has it.

No. Most ham rigs made since 1980 don't actually produce an AM signal, they
produce a double sideband reduced carrier signal. Ham rigs produce a signal
by taking an AM signal and running it through a filter to remove
the carrier and the other sideband.

Their "AM" mode signal is made by recombining the the upper and lower sideband
signals, with only a tiny residual carrier.

Most AM receivers can receive this signal, but there is no carrier to lock
on to, so I doubt that a sync detector can lock onto them.

But that's exactly the situation for a synchronous detector.

An AM signal reaches your receiver, but the carrier is too weak due to
selective fading. The issue is the strength of the carrier to the
sidebands, if the carrier is too weak it will sound like overmodulation
(which it is, just at the receiver rather than transmitter).

You can reinsert the carrier at the receiver, but with DSB of some sort,
you don't know where to set it properly. It's not just the issue of
single sideband where a mistuned receiver will shift the audio by a
certain amount (which one can live with), but with DSB if each sideband
doesn't translate down to the same audio frequency (which would happen
if the BFO isn't in the right spot), then the two sidebands clash. If
the incoming carrier is weak, the issue of beating against the local
carrier from the BFO is a secondary issue.

A sync detector figures out where to place the missing carrier whether
the carrier is weak or not, or even whether there is a carrier. It
doesn't matter if the carrier was weak compared to the sidebands when
the signal left the transmitter, for if the carrier was weakened along the
way to your receiver.

Which brings up another issue. Everyone talks about sync detectors, but
there are a variety of schemes, which do end up operating differently.
People think the sync detector is vital, yet then "some work better than
others". Some of that may be due to the specific scheme used to provide
the feature, while in other cases it can be due to bad implementation of
a specific scheme.

The stereotype of the phase locked loop locking to the carrier of the
incoming signal and then that is used as the BFO to translate the signal
down to audio, that may be the least used. It's certainly similar to
schemes where the carrier is simply amplified a lot in reference to the
sidebands (like the scheme to use a Q-multiplier to raise the level of
the incoming carrier compared to the sidebands) or a very narrow IF strip
is used to isolate and amplify the incoming carrier and then fed to the
product detector. They work, but if the carrier disappears, they go out
of lock, and they certainly aren't as versatile as some others. (I gather
the Drake R7 used a detector along these lines).

There was a whole wave of detectors for DSB in "Ham Radio" magazine in
the seventies, and the next scheme up was to get the location of the
missing carrier by looking at the sidebands. Double the frequency of
the incoming signal, and then divide it back, and you'd get a signal
right in the middle. Since the sidebands are duplicate of each other
Use a town at the transmitter to make it simple, a 1KHz tone. A 10MHz DSB
signal will then have an output at 9.999MHz and 10.001MHz, if you add
those up you will get 10MHz, and it will remain 10MHz no matter where that
tone goes. The 10MHz is exactly in the right spot to properly translate
the sidebands back to audio, and that's what you want.

When Webb described the "synchronous detector" in CQ about 1958, the
intent was to demodulate DSB with no carrier. (The carrier doesn't carry
content, it just means you don't need a BFO at the receiver or a means to
know where it should be set, but the carrier does use power, while the two
sidebands provide information about where the carrier should be, and allow
for some level of diversity reception by selecting one of the two
sidebands.). It doesn't lock to the carrier, since no carrier was
expected. It uses information from outputs of the product detectors (yes
two of them) to show where to place the reinserted carrier. It works with
any DSB signal, whether it has a carrier or not. It won't demodulate SSB
since there is no information on where to place the BFO in reference to
the sideband, you need to unlock the loop since the PLL will otherwise
try to lock to what it can't find and thus not tune properly. This type
of detector is very similar to the "sideband slicer" and other such
products that used the phasing method of sideband reception for SSB,
allowing one to select upper or lower sideband by the proper combination
of phased signals, the addition being the circuitry to lock the BFO
to the proper place.

I gather that's the common type of sync detector in most receivers
nowadays, but I don't know for sure. One can have that sort of
arrangement, that does lock to the sidebands, without fully decoding
the two sidebands separately, and there seems to be receivers that don't
provide for that selectible sideband.

Michael

Grundig 750 or Grundig G3

On Wed, 31 Mar 2010, SC Dxing wrote:

Bruce,

My G5 can do SSB but it's via a fine tune knob. Not separate USB/LSB.
I can't really complain about the G5, I think I just want a new toy to
play with.

But that's not some different technique, it's just cheaper.

it's cheaper to have a variable oscillator as the BFO than two crystals to
allow for a fixed BFO that is properly placed for upper and lower
sideband. Crystals cost money, the tuneable BFO is cheaper and allows
for a level of fine tuning (though once you use it for fine tuning, you
lose the ability to place it right where it should be on the slopes of
the IF filter, but with a tuneable BFO you'd only be guessing anyway).

In both cases, there is a BFO. Some people seem confused by that, since
in the old days of a tuneable BFO, the knob was labelled BFO, but once
sideband receivers came along with crystal controlled BFOs, the knob
was labelled "mode" or "sideband".

With a sync detector, you need a tuneable BFO anyway to lock to the
incoming signal, so there's little sense in tossing that out for a
crystal controlled BFO for SSB reception.

Michael

Grundig 750 or Grundig G3

Geoffrey S. Mendelson wrote:
Bob Dobbs wrote:
When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.
If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.
note* - there isn't a way to engage the sync-det in either of the SSB modes on
the only radio I have that has it.

No. Most ham rigs made since 1980 don't actually produce an AM signal, they
produce a double sideband reduced carrier signal. Ham rigs produce a signal
by taking an AM signal and running it through a filter to remove
the carrier and the other sideband.

Their "AM" mode signal is made by recombining the the upper and lower sideband
signals, with only a tiny residual carrier.

Most AM receivers can receive this signal, but there is no carrier to lock
on to, so I doubt that a sync detector can lock onto them.

Geoff.

Actually, though transceivers vary, most do produce a real AM
signal. (The old Drake C-lines produced DX-60-like "controlled
carrier" screen modulation, which _is_ AM though the average carrier
level goes up and down with modulation. A few older Collins and
other SSB transceivers just insert carrier on an SSB signal,
producing a rather distorted poor excuse for an AM signal called
"AME" or "AM equivalent." But they're rare. Most transceivers today
generate real AM.)

They do this by either bypassing the SSB filter or replacing it with
a wider one, and then unbalancing the balanced modulator by adding
an adjustable DC component to its audio input port. When the audio
and DC levels are balanced correctly, this can produce perfect
amplitude modulation. (Some amateurs, of course, don't adjust things
correctly, which can cause distortion and other problems.)

Before all my equipment was stolen with the complicity of the FBI, I
had a modified Kenwood TS440S which used this scheme. The stock 440
produced pretty good AM, but I wanted better. The modifications
included bypassing the low IF filters entirely in the AM transmit
mode, and reconfiguring the audio chain for better waveform
fidelity. It produced 25 watts of AM with better quality than many
broadcast stations.

With all good wishes,

Kevin, WB4AIO.
--
http://kevinalfredstrom.com/

Grundig 750 or Grundig G3

Michael Black wrote:
[...]

When Webb described the "synchronous detector" in CQ about 1958, the
intent was to demodulate DSB with no carrier. (The carrier doesn't
carry content, it just means you don't need a BFO at the receiver or a
means to know where it should be set, but the carrier does use power,
while the two sidebands provide information about where the carrier
should be, and allow for some level of diversity reception by selecting
one of the two sidebands.). It doesn't lock to the carrier, since no
carrier was expected. It uses information from outputs of the product
detectors (yes
two of them) to show where to place the reinserted carrier. It works
with any DSB signal, whether it has a carrier or not. It won't
demodulate SSB since there is no information on where to place the BFO
in reference to
the sideband, you need to unlock the loop since the PLL will otherwise
try to lock to what it can't find and thus not tune properly. This type
of detector is very similar to the "sideband slicer" and other such
products that used the phasing method of sideband reception for SSB,
allowing one to select upper or lower sideband by the proper combination
of phased signals, the addition being the circuitry to lock the BFO
to the proper place.

I gather that's the common type of sync detector in most receivers
nowadays, but I don't know for sure. One can have that sort of
arrangement, that does lock to the sidebands, without fully decoding
the two sidebands separately, and there seems to be receivers that don't
provide for that selectible sideband.

Michael

The type of sync detector that needs no carrier whatever in order to
lock on a DSB signal is called a Costas loop -- after John P.
Costas, who invented it. (Costas, by the way, did make a few rare
appearances on high-fidelity 40 and 75 meter amateur AM well into
the 2000s. He died in 2008.)

Sadly, no commercial receiver I am aware of uses a Costas loop. They
all use some form of carrier lock.

The last time I tuned a receiver with a Costas loop in it was in
1975, at the home of W3DUQ, using his National HRO-60 with his
homebrew 7360-based stereo sync system. It was amazing, and gave you
the ability to copy signals so deep in interference that you simply
couldn't believe it.

Interestingly, the (now out of production) Racal 6790 series used a
form of exalted carrier sync detection in which the incoming AM
signal was limited in the same way an FM detector limits, stripping
off all amplitude-modulated components.

Then the amplitude-limited carrier was applied to the carrier input
of the product detector to detect the AM signal.

This allowed for good sync detection (except perhaps for _extremely
deep_ selective fades) with the added benefit that _the signal was
always locked_. There were no heterodynes while tuning or if an
off-frequency station broke in on the QSO. It tuned just like a
regular diode detector AM receiver, with AM signals always
demodulated properly even as you tuned through them. If anyone wants
to give me one of those Racals, I'll take it.

With all good wishes,

Kevin, WB4AIO.
--
http://kevinalfredstrom.com/

Grundig 750 or Grundig G3

On 4/24/2010 9:11 AM, Kevin Alfred Strom wrote:

Before all my equipment was stolen with the complicity of the FBI...

Sounds like there is a story there. Would you care to elaborate?