On 1 Oct 2005 20:54:02 -0700, said in
rec.radio.scanner:

i guess i was trying to find out how many ways signal can be modulated.
even if the signal is digital, isn't it still modulated in fm?

Unless it's modulated in AM, SSB (which is really AM or FM, but we
usually use the term to mean one AM sideband) or some weird modulation
I haven't heard of.

Digital is the format of the data being used to modulate, FM is the
method of modulation.

It's like English/French vs. VHS/Beta. Either language can be put on
either tape format. Any data format (analog, any form of digital) can
be impressed on the amplitude of the carrier (AM), the frequency of
the carrier (FM) or, presumably on some other characteristic of the
carrier, if someone can come up with one.

When I think about what parameters of a carrier could be controlled with a
modulating signal, there's amplitude, frequency, phase, and waveshape, and
there are numerous ways to modulate these parameters, both continuous and
discrete. An example of waveshape modulation would be pulsewidth modulation
(PWM). It is possible to encode information digitally by modulating any of
those four parameters...it doesn't have to be FM. With more sophistication,
you could modulate more than one parameter at a time to get more information
out of a given bandwidth.

Have a look at "modulation" in Wikipedia
(http://en.wikipedia.org/wiki/Modulation).

- Doug


wrote in message
oups.com...
i guess i was trying to find out how many ways signal can be modulated.
even if the signal is digital, isn't it still modulated in fm?

On 1 Oct 2005 20:54:02 -0700, wrote:

i guess i was trying to find out how many ways signal can be modulated.
even if the signal is digital, isn't it still modulated in fm?
Actually most digital schemes use PM (yes there is such a thing, Phase
Modulation). At low modulation indices, with FM, you get Narrow Band
FM, which is mathematically the same as AM with about 25% modulation.
You can carry a lot more information more easily in a given bandwidth
with PM than you can with FM.

On Sat, 01 Oct 2005 17:49:28 -0400, Al Klein wrote:

On Sat, 01 Oct 2005 19:48:00 GMT, Korbin Dallas
said in rec.radio.scanner:

On Fri, 30 Sep 2005 23:45:46 -0400, Al Klein wrote:

On Sat, 01 Oct 2005 01:43:09 GMT, Korbin Dallas
said in rec.radio.scanner:

On Fri, 30 Sep 2005 11:29:31 -0400, Al Klein wrote:
On Fri, 30 Sep 2005 13:35:23 GMT, "Jim Hackett"
said in rec.radio.scanner:

Digital?

Most of what we call "digital" is NFM or SNFM.

Actually "Digital" is C4FM.

And the modulation on the carrier is??? AM? PM?? FM??

What bandwidth is it?

There's a difference between the process of putting information on the
carrier and the format that information comes in. The OP was asking
about the physical layer, as specified by "AM/FM ..." etc..

The standard is APCO 25, which defines BW to be 6Khz and Modulation as
C4FM.

Again - what's the physical layer? Id the frequency of the carrier
changed? The amplitude? The phase? Some other characteristic of it?
The OP wasn't asking about the logical layer (which is where C4FM
sits), he was asking about the physical layer.

Gee I don't know, Since it has FM in the NAME maybe its FM.
Or perhaps you prefer the Emission designator of 8K10F1E.

I always thought Modulation and Channel access methods are typically
placed at layer 1.

--
Korbin Dallas
The name was changed to protect the guilty.

On Mon, 03 Oct 2005 23:28:37 GMT, Korbin Dallas
said in rec.radio.scanner:

On Sat, 01 Oct 2005 17:49:28 -0400, Al Klein wrote:
Again - what's the physical layer? Id the frequency of the carrier
changed? The amplitude? The phase? Some other characteristic of it?
The OP wasn't asking about the logical layer (which is where C4FM
sits), he was asking about the physical layer.

Gee I don't know, Since it has FM in the NAME maybe its FM.
Or perhaps you prefer the Emission designator of 8K10F1E.

Point, head, whoosh.

I always thought Modulation and Channel access methods are typically
placed at layer 1.

Modulation is layer 1. "Channel access"? Wazzat? PL?

On 29 Sep 2005 21:18:12 -0700, wrote:

there has to be some other modes that normal scanners wouldn't decode.
any thoughts?


ISB, DSB ?

DRM?

On Tue, 04 Oct 2005 10:39:59 GMT, (Peter Newman)
said in rec.radio.scanner:

On 29 Sep 2005 21:18:12 -0700, wrote:

there has to be some other modes that normal scanners wouldn't decode.
any thoughts?

ISB, DSB ?

Any receiver that will receive SSB will also receive DSB, since both
sidebands are the same. ISB too, but only 1 at a time.

On Wed, 05 Oct 2005 21:18:23 -0400, Al Klein
wrote:

On Tue, 04 Oct 2005 10:39:59 GMT, (Peter Newman)
said in rec.radio.scanner:

On 29 Sep 2005 21:18:12 -0700, wrote:

there has to be some other modes that normal scanners wouldn't decode.
any thoughts?

ISB, DSB ?

Any receiver that will receive SSB will also receive DSB, since both
sidebands are the same. ISB too, but only 1 at a time.
Only if the IF is narrow enough to keep the other sideband out,
otherwise you get both at once.....

On Thu, 06 Oct 2005 20:37:32 -0700, matt weber
said in rec.radio.scanner:

On Wed, 05 Oct 2005 21:18:23 -0400, Al Klein
wrote:

On Tue, 04 Oct 2005 10:39:59 GMT, (Peter Newman)
said in rec.radio.scanner:

On 29 Sep 2005 21:18:12 -0700, wrote:

there has to be some other modes that normal scanners wouldn't decode.
any thoughts?

ISB, DSB ?

Any receiver that will receive SSB will also receive DSB, since both
sidebands are the same. ISB too, but only 1 at a time.
Only if the IF is narrow enough to keep the other sideband out,
otherwise you get both at once.....

A SSB receiver is one that has a bandwidth narrow enough to receive
only 1 sideband. If it's 6 KHz wide it's a DSB receiver. (Yes,
almost any ham receiver is either SSB or DSB, depending on the filter
you have running at the moment.)

Of course finding DSBSC signals on the air today is a bit difficult.
(They used to be much more prevalent, but ARC5s are expensive antiques
today, not cheap transmitters. And is there still 1 operational
DSB-100?)

Al Klein wrote:

On Thu, 06 Oct 2005 20:37:32 -0700, matt weber
said in rec.radio.scanner:

On Wed, 05 Oct 2005 21:18:23 -0400, Al Klein
wrote:

On Tue, 04 Oct 2005 10:39:59 GMT, (Peter Newman)
said in rec.radio.scanner:

On 29 Sep 2005 21:18:12 -0700, wrote:

there has to be some other modes that normal scanners wouldn't decode.
any thoughts?

ISB, DSB ?

Any receiver that will receive SSB will also receive DSB, since both
sidebands are the same. ISB too, but only 1 at a time.
Only if the IF is narrow enough to keep the other sideband out,
otherwise you get both at once.....

A SSB receiver is one that has a bandwidth narrow enough to receive
only 1 sideband. If it's 6 KHz wide it's a DSB receiver. (Yes,
almost any ham receiver is either SSB or DSB, depending on the filter
you have running at the moment.)

Of course finding DSBSC signals on the air today is a bit difficult.
(They used to be much more prevalent, but ARC5s are expensive antiques
today, not cheap transmitters. And is there still 1 operational
DSB-100?)

You can't assume that any filter over 3kHz or so is symetrical about the
'carrier' frequency just because that is the normal configuation of consumer
equipment.

Just for fun I am currently listening to an LSB conversation on 3763 kHz with
a 7.5 kHz filter and I cannot hear any sign of the conversation on 3765 - but,
the noise is a bit higher due to the wider filter. I wouldn't normally do this
but just had to try it. Of course, if I select DSB or ISB I get both signals,
although the 3765 conversation is inverted and shifted in frequency.

I don't know how much DSB is still on the air but a quick google search for
"double side band' gets over 12 million hits. It may not be encountered in
normal voice communications on HF and scanner frequencies but it is hiding in
other places and frequencies from a quick look at some of the hits.

Dave