RadioBanter - DSB SC Mode

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

On a sunny day (12 Jun 2006 11:20:24 -0700) it happened "Telstar Electronics"
wrote in
.com:

Hmmm... that's what I thought originally. Now I'm getting confused. I'm
real interested how this discussion shakes out...

Do not listen to him, it is 100% nonsense.

Very simply:
An AM detector is an 'enveloppe' detector,
a DSB and SSB detector is a 'product detector'.

You have seen that waveform I pointed out in fig 4 for a sine wave single
tone modulation, the amplitude of the RF signal dos not really look like a
sinewave does it?

So you hear sever distortion, in fact you cannot make out what it is.

In a product detector the BFO is the 'substitute' carrier, and multiplication
of one (SSB) or both (DSB) sideband[s] gives the original modulation.

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!

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 Sun, 11 Jun 2006 14:38:54 GMT, Jan Panteltje
wrote:

+++Something wrong here, DSB-SC received on a normal set can only be
+++made 'inteligible' if it is received as SSB.
+++SSB is simply one sideband of the 2 DSB sends, so your BFO is [just as]
+++critical.
+++If you BFO is of center (so you re-insert the wrong carrier) and your RX
+++filter already removed the other sideband, then you have all the 'duck'
+++sound of SSB.
+++Moderns CB sets have no 'DSB' option, only USB / LSB, so always use one
+++sideband.
+++In case a set DOES pass both sideband, you get double the problem....
+++
+++Maybe you mean something else by DSB-SC altogether? Leave SOME carrier?
**************************

DSB-SC reception is not restricted to just SSB-SC receivers. A DSB-SC
signal can be received by reinjecting the carrier, even on a DSB
receiver.

DSB-SC stands for Double Sideband Supressed Carrier.

james

On Sun, 11 Jun 2006 21:16:28 GMT, Jan Panteltje
wrote:

+++On a sunny day (11 Jun 2006 13:35:21 -0700) it happened "Telstar Electronics"
wrote in
oups.com:
+++
+++Not sure what you're talking about. When I say DSB... I'm referring to
+++what others call the AM mode.
+++
+++www.telstar-electronics.com
+++
+++
+++DSB-SC (as you originally referred to) stands for:
+++Double Sideband Suppressed Carrier.
+++So, if the carrier is surpressed, then you have only 2 sidebands if a signal
+++is present (single tone modulation), nothing if no modulation is present.
+++ http://www.ece.drexel.edu/courses/ECE-S306/lab3.pdf
+++Look at figure 4, for a single tone modulating audio signal.
+++You will notice it is quite different from AM!
+++
+++Normal AM is also DSB, but the carrier is not surpressed.
+++Better to say AM if you mean AM, DSB is often used for DSB-SC.
______________

AM == Double Sideband Full Carrier.

james

"Telstar Electronics" wrote in message
oups.com...
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.

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.

www.telstar-electronics.com

There is no carrier. It's like listening to LSB and USB at the same time. 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. 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

On Mon, 12 Jun 2006 18:34:51 GMT, Jan Panteltje
wrote:

+++On a sunny day (12 Jun 2006 11:20:24 -0700) it happened "Telstar Electronics"
wrote in
oups.com:
+++
+++Hmmm... that's what I thought originally. Now I'm getting confused. I'm
+++real interested how this discussion shakes out...
+++
+++Do not listen to him, it is 100% nonsense.
+++
+++Very simply:
+++An AM detector is an 'enveloppe' detector,
+++a DSB and SSB detector is a 'product detector'.
*****

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.

+++
+++You have seen that waveform I pointed out in fig 4 for a sine wave single
+++tone modulation, the amplitude of the RF signal dos not really look like a
+++sinewave does it?
+++
+++So you hear sever distortion, in fact you cannot make out what it is.
+++
*****

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. 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.

+++In a product detector the BFO is the 'substitute' carrier, and multiplication
+++of one (SSB) or both (DSB) sideband[s] gives the original modulation.
+++
+++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!
+++
***********

Since the information in both sidebands are indentical the only need
for the second sideband is to increase demodulated audio.

+++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.
+++

james

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

On Mon, 12 Jun 2006 23:50:21 GMT, Bob Dobbs EC42
wrote:

+++On Mon, 12 Jun 2006 16:17:21 -0500, DrDeath wrote:
+++
+++ There is no carrier.
+++
+++No Carrier - no propagation
******************

You have to remember that in DSB-SC and in SSB tranmission the audio,
modulating signal, spectrum is mixed up to the desire frequency range.
In these voice signals the audio is now moved u p in the frequency
spectrum. That is essentially what modulation does, frequency
transform. In both DSB-SC and SSB, your are now transmitting a band of
frequencies that is equaly to the voice bandwidth at varying power
densities.

In DSB-LC, the carrier goes along for the ride to demodulate the
signals at the receiver. The carrier does not carry ant information at
all.

james

Telstar Electronics wrote:
Hmmm... that's what I thought originally. Now I'm getting confused. I'm
real interested how this discussion shakes out...

www.telstar-electronics.com
indeed a something close to a flamefest of a what to call mode

oh well at least it is a reasonably on topic post for once

personaly I like basci AM well enough although I use SSB on cb since I
can't legaly boost the power level but in ham bands I love AM better

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

"Telstar Electronics" wrote in message
oups.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. If you set both rigs to AM and lower the
deadkey to say an 1/8 watt with 15 watts of swing you can understand the low
dead key rig.