RadioBanter - DSB SC Mode

RadioBanter (https://www.radiobanter.com/)

- CB (https://www.radiobanter.com/cb/)

- - DSB SC Mode (https://www.radiobanter.com/cb/96297-dsb-sc-mode.html)

On a sunny day (Mon, 12 Jun 2006 23:42:59 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.42.57.909000@Quetzalcoatl:

On Mon, 12 Jun 2006 13:42:26 -0700, Telstar Electronics wrote:

So let me get this straight... In DSB-SC... both sidebands are
transmitted... but there is no carrier sent at all? Correct?... and the
carrier is re-inserted at the receiver.

That's what Panteltje would have you believe.
Without a carrier there would be no RF propagation.

Now with the swing set-up... both sidebands are transmitted... along
with the carrier... but the carrier's amplitude changes from extremely
low to a normal AM carrier when the modulation is added.

That's right, the supressed carrier becomes un-supressed according to the
amplitude of the Modulation, otherwise there wouldn't be a signal.

IOW: Supress the carrier out entirely and all you have is audio, no radio
propagation, have to shout real loud to get any DX out of that.

Sorry dude, the sidebands are RF.

On a sunny day (Mon, 12 Jun 2006 23:50:21 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.50.19.219000@Quetzalcoatl:

On Mon, 12 Jun 2006 16:17:21 -0500, DrDeath wrote:

There is no carrier.

No Carrier - no propagation

It's like listening to LSB and USB at the same time.

That's what an AM receiver does.

If you remove half the ssb signal, say LSB, you would hear more of the
donald duck sound due to the reduced size of the bandwidth.

Not bandwidth reduction, but the lacy of waveform symetry

Just forget AM carrier when talking DSB-SC as it just isn't there. DSB
is AM and when the carrier is removed you have DSB-SC

As I've tried to point out
with out a carrier there isn't propagation.
why do you think they call it "supressed" carrier

Because it ain't there anymore, just like in SSB.

instead of removed carrier?
Because they already used 'removed' for brain.

On a sunny day (Tue, 13 Jun 2006 00:44:15 GMT) it happened james
wrote in :

On 12 Jun 2006 13:42:26 -0700, "Telstar Electronics"
wrote:

+++So let me get this straight... In DSB-SC... both sidebands are
+++transmitted... but there is no carrier sent at all? Correct?... and the
+++carrier is re-inserted at the receiver.
+++
*************

Not exactly. Supressed carrier is just that. The carrier is suppressed
by a desired amount measured in dBs. It can be fully suppressed or
partially supressed.

+++Now with the swing set-up... both sidebands are transmitted... along
+++with the carrier... but the carrier's amplitude changes from extremely
+++low to a normal AM carrier when the modulation is added.
+++
*************

There is several techniques that has been used in amatuer radio for
many decades. One stems from the old tube days called grid modulation.
What happens here is that the modulated stage, usually the final RF
stage, has the modulation signal applied to the grid of the tube. By
varying the grid voltage at an audio rate, the bias on the tube
varies. This will change the gain of the tube. What happens then is
when there is no modulation signal the tube is at or near cutoff and
there is little carrier. As you modulate the carrier varies at an
audio rate. Disadvantage of this method is the maximum percentage of
modulation is about 85%.

Another method is one sed by the Drake 4 line series of transmitters.
This is where modulation is applied to a low level stage. Usually a
balanced modulator. To achieve AM, the balanced modulator is slightly
kicked off balanced to allow a small amount of carrier to appear at
the output. With modualtion this will vary some. Subsequent stages of
amplification will bring the signal up to the desired level.

james

100% agreed.

On a sunny day (Mon, 12 Jun 2006 21:01:33 -0500) it happened "DrDeath"
wrote in :

"Telstar Electronics" wrote in message
roups.com...
Yes... at least the discussion is something interesting... instead of
dougie this and dougie that... whoever dougie is... LOL

I still trying to research this topic.... since there seems to be
considerably different views of DSB-SC out here. I'm starting to think
my original statement that a very high swing AM transmission can be
considered a DSB-SC... and requires no special BFO tuning.

www.telstar-electronics.com

Nope, if you listen with your rig set to AM and the transmission is DSB-SC
you will hear a garbled mess.

Exactly!

I thought this was very helpful for me.
http://www.williamson-labs.com/480_dsb.htm
It shows that in DSB-SC... both sidebands are transmitted (they are RF)
and that no carrier is ever transmitted. The carrier would have to be
added back at the receiver. I believe that would have the same critical
tuning issues as SSB.

I'm not sure why anyone would want to do this as all the intelligence
is contained in a single sideband anyway.

So it appears that DSB-SC is not much different than SSB-SC. I guess
that really figured.

I was wrong in using DSB-SC and a mode that is basically AM (with a
greatly reduced carrier that increases via modulation) interchangeably.
It now is apparent they are not the same.

www.telstar-electronics.com

Jan

I don't have to go through your exercises, I am very well familiar
with diode ring demodulators and various other techniques to
demodulate audio in amplitude modualted sysytems. I am well aware of
the trade offs in effectiveness and costs of may different aprroaches.

james
On Tue, 13 Jun 2006 10:15:08 GMT, Jan Panteltje
wrote:

+++On a sunny day (Tue, 13 Jun 2006 00:32:38 GMT) it happened james
wrote in :
+++
+++A product Detector is prefered due to its mixer characteristics. Being
+++balanced, the two inputs are supressed sufficiently to make filtering
+++their components in the output much easier. Product detectors and
+++Envelope dection is not the only means of detecting DSB-SC and DSB-LC
+++signals. They are the most simplest and easiest to implement.
+++
+++I have used sampling to demodulate QAM, In any color TV you will find it,
+++carrier is regenerated in phase from the color burst, look up NTSC.
+++And there we have 2 modulating systems, here is how that works in the
+++time domain:
+++ http://groups.google.com/group/sci.e...ce23fcbb253646
+++
+++The main thing is perhaps that you can see that in SSB, if we have 1MHz
+++carrier, and 1kHz sine modulation, we get a 1.001 MHz carrier (or 0.999 if
+++the other sideband is used.
+++So to get the original back, it would be sufficient to substract the 1MHz
+++again in the first case (1.001 - 1) = 1kHz, or in the other case 1 - .999.
+++
+++In the DSB-SC case we would have 1.001 AND .999 AT THE SAME TIME.
+++
+++Using one sideband is enough. DSB uses double the bandwidth and as such
+++is less efficient then SSB,
+++
+++Distortion of the RF waveform may not nescessarily indicate that the
+++detected audio is unintelligable. As long as the recovered audio is
+++reproduced accuarately during demodulation then there is no
+++distortion.
+++
+++But it won't [work].
+++What the 4 diode ring modulator does, is make a RF amplitude phase phi
+++when the audio signal goes positive proportional to the audio amplitude,
+++and the same with phase phi+180 degrees when the audio signal goes negative.
+++If you do AM envelope detector (as the you normally do with a diode and RC
+++lowpass) you get a wave form that is no longer a sine, but looks like double
+++phase rectified sine when filtered.
+++
+++
+++ Spectral content of the demodualted signal can be set by
+++post detection filtering. This can reduce to some extent the harmonics
+++of the modulating signal.
+++
+++
+++
+++By the way the lab you point to is more about the generation of a DSB
+++signal. From figure 4 you are making statements about demodulation.
+++
+++Of course, lok at that waveform, build a 'non distorting AM detector
+++for it without carrier re-insertion (BFO, some oscillator), you CANNOT.
+++Modulation /demodulation is related.
+++
+++Please build one, try it,
+++
+++Since the information in both sidebands are indentical the only need
+++for the second sideband is to increase demodulated audio.
+++
+++Yes, we agree here.
+++
+++Please try it:
+++
+++But for the non-believers, try it out, all you need is an audio amp,
+++oscillator, 4 diodes, and of course a 27 HHz xtal oscillator.
+++http://www.nzart.org.nz/nzart/examin...les/Mixers.htm
+++There is a description and diagram a bit down on the page.
+++
+++Listen to it on an AM receiver, and you will KNOW.
+++

On Tue, 13 Jun 2006 10:18:17 GMT, Jan Panteltje
wrote:

+++On a sunny day (Mon, 12 Jun 2006 23:34:57 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.34.54.717000@Quetzalcoatl:
+++
+++On Mon, 12 Jun 2006 18:34:51 +0000, Jan Panteltje wrote:
+++
+++ There is in fact no need for the 'other' sideband in DSB-SC, no problem
+++ if the receiver filters it out, that is why you can receive DSB-SC both
+++ with USB and LSB!
+++
+++Without both sidebands, it would no longer be DSB, and the reason stations
+++use DSB instead of SSB is for the use of ordinary receivers that lack a
+++BFO.
+++
+++How about providing a source of those 'undetectable" DSBSC signals that
+++one might encounter within or nearby to the CB band, instead of some
+++technobabble with irrelevant circuitry illustrations?
+++
+++OK for the last time before you enter my killfile:
+++DSB is not AM. AM is AM, and AM has both sidebands, but when we say 'DSB we mean DSB-SC.
+++idiot
+++
+++
+++
+++
**************************

We seem to be hung up on abbreviations and their applications to
analog communications.

A list of Abbreviation in analog Modulation from Introduction to
Communications System Third Edition by Ferrel G. Stremler. This is
taken from my Communications Textbook from college.

1)AM AMplitude Modulation: A CW modulation using amplitude variation
in proportion to the amplitude of the modulating signal. Usually taken
as DSB-LC for commercial broadcast transmission and DSB-SC for
multiplexed systemes.

2) CW COntinuous Wave: A carrier signal (usually sinusoidal) used for
modulation or keying.

3) DSB Double Sideband(LC or SC): a signal having two spectral
sidebands symetrically balanced with respect tothe carrier frequency.

4) LC Large Carrier: a signal in which a relatively large proprotion
of the spectrum is concentrated at the carrier frequency ( used with
DSB, SSB, and VSB).

5) SC Supressed Carrier: a signal in which a relatively small
proportion (ideally zero) of the spectrum is is concentrated at the
carier frequency ( used with DSB, SSB, VSB).

Now translating into CB lingo AM and DSB-LC are synonymous. That is
what nearly all off the shelf AM CB radios produce. Modulation takes
place in the final stage before the antenna. There are some that use
low level modulation that follow the modulated stage with further
amplification afterwards to raise the power density to a level to
effect the desired communication range with the intended antenna
system.

Please note that the difference between Large Carrier and Suppressed
carrier can be used with DSB, SSB and VSB amplitude systems. The
difference is the role the carrier itself plays in demodulaztion ONLY!
In DSB it is generally accepted that both sidebands carry the same
information during modualation. SSB is defined as a spectrum in which
only one sideband is trransmitted with or without the carrier.
Vestigial Sideband is where one full sideband is and a partial of the
other sideband is not fully transmitted. TV signals are VSB signals.

hope this helps

james

"Jan Panteltje" wrote in message
...

I did a nice frequency counter on an FPGA lab board:
http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2

And just how do you open/view such a beast? WinRAR opened the file, but
left me with another file that was unknown and completely useless... If you
are trying to make a point, you might want to put it in a format that humans
can actually use...

PowerHouse Communications schreef:

"Jan Panteltje" wrote in message
...

I did a nice frequency counter on an FPGA lab board:
http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2

And just how do you open/view such a beast? WinRAR opened the file, but
left me with another file that was unknown and completely useless... If you
are trying to make a point, you might want to put it in a format that humans
can actually use...

'bz2' is a compressed format, it is open source, and frequently used in
Linux.
It has a higher compression ratio then for exmpel 'zip' or tgz.
the correct way to 'unpack' it in Linux / unix is:
tar -jxvf frequency_counter-0.2.1.bz2
In MS windows there is as far as i knwo no correct way to do anything,
so I
cannot help you there.
You would only find verilog source files anyways, and then complain you
cannot read verilog (language), that posting really was on level3, you
were still on level 1.

wrote in message
oups.com...

PowerHouse Communications schreef:

"Jan Panteltje" wrote in message
...

I did a nice frequency counter on an FPGA lab board:
http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2

And just how do you open/view such a beast? WinRAR opened the file, but
left me with another file that was unknown and completely useless... If
you
are trying to make a point, you might want to put it in a format that
humans
can actually use...

'bz2' is a compressed format, it is open source, and frequently used in
Linux.
It has a higher compression ratio then for exmpel 'zip' or tgz.
the correct way to 'unpack' it in Linux / unix is:
tar -jxvf frequency_counter-0.2.1.bz2
In MS windows there is as far as i knwo no correct way to do anything,
so I cannot help you there.

Like I told you, WinRAR opened (uncompressed) the file (unpack[ed] it in
your language)...

You would only find verilog source files anyways, and then complain you
cannot read verilog (language), that posting really was on level3, you
were still on level 1.

I could really give a **** less what planet you are on, I asked a simple
question, all you had to do was answer it without your nasty attitude.

It was nice of you to provide a link, however I'd roughly guess that over
98% of the people reading this group, including the person you replied to,
does not use Linux, and therefore would have no use for the file. Oh, and
since you have a cocky attitude about you, let me return the favor... IT'S
"example", NOT "exmpel"!