Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Hi:

Hypothetical situation: a PCM audio signal [24-bit and monoaural] is
transmitted through an analog 3 Mhz AM carrier, an AM receiver on the
other end [tuned to 3 Mhz] picks up the signal, and the reciever is
attached to a device that can recieve, process, and decode the PCM
audio back to analog and then send it to a loudspeaker. However -- in
this theoretical situation -- the environment is filled with EMI, RFI,
and heterodynes that affect all AM stations.

My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?


Thanks,

Radium

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

You guess correct, assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient. You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use of
the RF bandwidth.

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Mike Gathergood (G4KFK) wrote:
Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

You guess correct,
assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

What is FEC?

But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient.

Isn't 3 Mhz enough to transmit a data rate of 1.06 mbps?

44,100 X 24 = 1,058,400

You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use of
the RF bandwidth.


Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Radium wrote:
What is FEC?

Forward Error Correction. Google it :-)

Isn't 3 Mhz enough to transmit a data rate of 1.06 mbps?

Yes - but the chipsets to compress the digitised audio are much cheaper
than the notional value of the bandwidth you would be trashing with
your 24bit PCM.

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Mike Gathergood (G4KFK) wrote:
Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

You guess correct, assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

What if FEC is not used?


But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient. You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use of
the RF bandwidth.

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Mike Gathergood (G4KFK)" wrote in message
oups.com...

Radium wrote:
What is FEC?

Forward Error Correction. Google it :-)


Just to add to Mike's comment, FEC works by send the same message several
times- in simple terms, in the hope that one with get through correctly. It
is simple to implement, your recieving system just needs to be able to
identify a correct message and use it, not spot a bad message and initiate
either a request for resend or applly some sort of correction method
(assuming there is error correcting code in the message).


--
73
Brian
www.g8osn.org.uk

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Brian Reay wrote:
"Mike Gathergood (G4KFK)" wrote in message
oups.com...

Radium wrote:
What is FEC?

Forward Error Correction. Google it :-)


Just to add to Mike's comment, FEC works by send the same message several
times- in simple terms, in the hope that one with get through correctly. It
is simple to implement, your recieving system just needs to be able to
identify a correct message and use it, not spot a bad message and initiate
either a request for resend or applly some sort of correction method
(assuming there is error correcting code in the message).


--
73
Brian
www.g8osn.org.uk

These comms are in one direction, so you don't resend a packet as there
is no way to make such a request. In practice, the codes have both
error detection and correction capabilities, so to the degree the
coding allows, the signal can be corrected with the bits that were
received. Note nobody mentioned a modulation scheme for sending this
data.

As a bit of trivia, Reed Solomon encoding was invented without a way to
decode it. That's what you get when you let mathematicians run wild.
For absolutely nothing of any value other than bragging rights, name
the guy who invented the decoding scheme for Reed Solomon. [Hopefully
this isn't wikied someplace. I did one class in grad school on error
detection and correction, and it was a pain in the ass if you get into
the theory. Implementation is quite simple.]

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Radium wrote:
Mike Gathergood (G4KFK) wrote:
Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

You guess correct, assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

What if FEC is not used?

With no FEC, your receiver would be more prone to those errors that you
were worried about in the first place.



But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient. You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use of
the RF bandwidth.

Just to amplify on this, anything that you can do to reduce the
bandwidth of the digital signal before it's used to modulate the
transmitter will help. One very big advantage is that you can wind down
the bandwidth of the receiver, thus reducing the level of background
noise in the system.

Why did you choose 3MHz? What's the application?

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Brian Reay wrote:
Just to add to Mike's comment, FEC works by send the same message several
times- in simple terms, in the hope that one with get through correctly. It
is simple to implement, your recieving system just needs to be able to
identify a correct message and use it, not spot a bad message and initiate
either a request for resend or applly some sort of correction method
(assuming there is error correcting code in the message).

FEC is generally used in applications where you don't have time to
request a retransmission of an errored packet, and/or where the
transmission path is simplex, and/or where there are multiplex
receivers for a single transmitter.

If you have the luxuries of time and a full-duplex point-to-point
environment, ARQ is better.

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Mike Gathergood (G4KFK) wrote:
Radium wrote:
Mike Gathergood (G4KFK) wrote:
Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

You guess correct, assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

What if FEC is not used?


With no FEC, your receiver would be more prone to those errors that you
were worried about in the first place.

What would these errors sound like?




But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient. You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use of
the RF bandwidth.

Just to amplify on this, anything that you can do to reduce the
bandwidth of the digital signal before it's used to modulate the
transmitter will help. One very big advantage is that you can wind down
the bandwidth of the receiver, thus reducing the level of background
noise in the system.


Why did you choose 3MHz?

44,100 X 24 = 1,058,400

1,058,400 bps requires that the frequency of the carrier be at least
2,646,000 Hz. To make it safe, use 3 MHz.

What's the application?

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
..00000001 dB. Most likely, what would I hear?


Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

wrote:
As a bit of trivia, Reed Solomon encoding was invented without a way to
decode it. That's what you get when you let mathematicians run wild.
For absolutely nothing of any value other than bragging rights, name
the guy who invented the decoding scheme for Reed Solomon. [Hopefully
this isn't wikied someplace. I did one class in grad school on error
detection and correction, and it was a pain in the ass if you get into
the theory. Implementation is quite simple.]

It makes sense. The encoding software had to be ready to put into a probe
before the launch date. Once it was up it could not be changed.

Decoding software was another matter. Since they had years, maybe even decades
to decode the data, and it did not have to be real time, they could continue
to work on it.

All they had to do is not loose the tapes. :-(

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Radium wrote:
What would these errors sound like?

An error in a PCM system would manifest itself as a difference between
what you put in at the analogue input to the transmitter, and what you
got out of the analogue output of the receiver.

The magnitude and polarity of the difference would depend entirely on
whether the bit error was the MSB (polarity would be wrong), or one of
the LSBs (the amplitude would be wrong). It wouldn't "sound" like
anything in particular.

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?

Have a look he http://www.imdb.com/title/tt0375210/ :-)

Seriously though, I have no idea. Why don't you try it and post the
results here?

Cheers
Mike

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Mike Gathergood (G4KFK) wrote:
Radium wrote:
What would these errors sound like?

An error in a PCM system would manifest itself as a difference between
what you put in at the analogue input to the transmitter, and what you
got out of the analogue output of the receiver.

The magnitude and polarity of the difference would depend entirely on
whether the bit error was the MSB (polarity would be wrong), or one of
the LSBs (the amplitude would be wrong). It wouldn't "sound" like
anything in particular.

What about the heterodyne tones present on analog AM radio? Would they
be audible on a linear-PCM receiver that receives PCM signals on an AM
station?

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?

Have a look he http://www.imdb.com/title/tt0375210/ :-)


Seriously though, I have no idea. Why don't you try it and post the
results here?

Easy for you to ask. I doubt any store has the device. And the
equipment required to amplify .00000000001 dB to an audible level would
take up the entire room.

So the best I could do -- at least for the moment -- is guess.

I am aware though that just because the PCM-receiver is digital does
not mean its completely immune to heterodynes, EMI, or RFI. If the
heterodyne, EMI or RFI has a waveform that sufficiently resembles a PCM
signal, it may very well be picked up by the PCM-receiver that is
connected to the AM receiver.

Physically, the digital reciever is still an electronic device and
hence it has some reception of EMI, RFI, and heterodynes. Its just not
affected as much as an analog receiver would be.

Cheers
Mike

I've seen that "white noise" movie. But thats more like Sci-Fi. Yet it
is one thing that gave me the interest to hear whatever is buried DEEP
in background noise.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

On 9/12/06 3:57 PM, in article
, "Radium"
wrote:


Mike Gathergood (G4KFK) wrote:
Radium wrote:
What would these errors sound like?

An error in a PCM system would manifest itself as a difference between
what you put in at the analogue input to the transmitter, and what you
got out of the analogue output of the receiver.

The magnitude and polarity of the difference would depend entirely on
whether the bit error was the MSB (polarity would be wrong), or one of
the LSBs (the amplitude would be wrong). It wouldn't "sound" like
anything in particular.

What about the heterodyne tones present on analog AM radio? Would they
be audible on a linear-PCM receiver that receives PCM signals on an AM
station?

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?

Have a look he http://www.imdb.com/title/tt0375210/ :-)


Seriously though, I have no idea. Why don't you try it and post the
results here?

Easy for you to ask. I doubt any store has the device. And the
equipment required to amplify .00000000001 dB to an audible level would
take up the entire room.

There is no such thing as a .00000000001 dB signal

So the best I could do -- at least for the moment -- is guess.

I am aware though that just because the PCM-receiver is digital does
not mean its completely immune to heterodynes, EMI, or RFI. If the
heterodyne, EMI or RFI has a waveform that sufficiently resembles a PCM
signal, it may very well be picked up by the PCM-receiver that is
connected to the AM receiver.

Physically, the digital reciever is still an electronic device and
hence it has some reception of EMI, RFI, and heterodynes. Its just not
affected as much as an analog receiver would be.

In fringe areas, analog cell phones could be well understood despite the
poor signal-to-noise ratio. Digital cell phones in a fringe area just quit
working, or lose sync and you hear bits of other conversations.




Cheers
Mike

I've seen that "white noise" movie. But thats more like Sci-Fi. Yet it
is one thing that gave me the interest to hear whatever is buried DEEP
in background noise.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Don Bowey wrote:
On 9/12/06 3:57 PM, in article
, "Radium"
wrote:


Mike Gathergood (G4KFK) wrote:
Radium wrote:
What would these errors sound like?

An error in a PCM system would manifest itself as a difference between
what you put in at the analogue input to the transmitter, and what you
got out of the analogue output of the receiver.

The magnitude and polarity of the difference would depend entirely on
whether the bit error was the MSB (polarity would be wrong), or one of
the LSBs (the amplitude would be wrong). It wouldn't "sound" like
anything in particular.

What about the heterodyne tones present on analog AM radio? Would they
be audible on a linear-PCM receiver that receives PCM signals on an AM
station?

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?

Have a look he http://www.imdb.com/title/tt0375210/ :-)


Seriously though, I have no idea. Why don't you try it and post the
results here?

Easy for you to ask. I doubt any store has the device. And the
equipment required to amplify .00000000001 dB to an audible level would
take up the entire room.


There is no such thing as a .00000000001 dB signal

Whats stops a .00000000001 dB signal from existing?


So the best I could do -- at least for the moment -- is guess.

I am aware though that just because the PCM-receiver is digital does
not mean its completely immune to heterodynes, EMI, or RFI. If the
heterodyne, EMI or RFI has a waveform that sufficiently resembles a PCM
signal, it may very well be picked up by the PCM-receiver that is
connected to the AM receiver.

Physically, the digital reciever is still an electronic device and
hence it has some reception of EMI, RFI, and heterodynes. Its just not
affected as much as an analog receiver would be.


In fringe areas, analog cell phones could be well understood despite the
poor signal-to-noise ratio. Digital cell phones in a fringe area just quit
working, or lose sync and you hear bits of other conversations.






Cheers
Mike

I've seen that "white noise" movie. But thats more like Sci-Fi. Yet it
is one thing that gave me the interest to hear whatever is buried DEEP
in background noise.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Don Bowey" wrote in message
...
There is no such thing as a .00000000001 dB signal

Sure there is. It's very close in amplitude to a 0.0dB signal. ;-)

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Radium" wrote in message
oups.com...
Hi:

Hypothetical situation: a PCM audio signal [24-bit and monoaural] is
transmitted through an analog 3 Mhz AM carrier, an AM receiver on the
other end [tuned to 3 Mhz] picks up the signal, and the reciever is
attached to a device that can recieve, process, and decode the PCM
audio back to analog and then send it to a loudspeaker. However -- in
this theoretical situation -- the environment is filled with EMI, RFI,
and heterodynes that affect all AM stations.

My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

Depends.
What is the transmitter power? What is the separation
between the transmitter and receiver?


I ask because I think -- but definitely don't know -- that because the
received signal is digital, it is less likely that the EMI, RFI, and
heterodynes would cause noticeable auditory disruptions when compared
to analog. Do I guess correct?

If there is a decent SNR you are correct.
If the SNR falls below a certain value then
the reverse is true.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Tim Williams wrote:

"Don Bowey" wrote in message
...
There is no such thing as a .00000000001 dB signal

Sure there is. It's very close in amplitude to a 0.0dB signal. ;-)


dB without a reference is meaningless. How can you have a ratio
without a reference?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Radium" wrote in message
oups.com...

Mike Gathergood (G4KFK) wrote:
Radium wrote:
Mike Gathergood (G4KFK) wrote:
Radium wrote:
My question: Will the received PCM audio signal remain noticeably
"clean" to the listener or will he/she notice the EMI, RFI, and
heterodynes affecting the audio?

I ask because I think -- but definitely don't know -- that because
the
received signal is digital, it is less likely that the EMI, RFI,
and
heterodynes would cause noticeable auditory disruptions when
compared
to analog. Do I guess correct?

You guess correct, assuming that FEC is applied to the digital signal
before it is used to modulate the transmitter.

What if FEC is not used?


With no FEC, your receiver would be more prone to those errors that you
were worried about in the first place.

What would these errors sound like?




But you wouldn't do it that way anyway. Raw PCM is too bandwidth
inefficient. You'd use MPEG layer 2, or apt-X, or something like that
to reduce the bandwidth without noticeably degrading the audio
quality.
You'd probably also multiplex several different channels (programmes)
together onto one RF carrier as well, to make better statistical use
of
the RF bandwidth.

Just to amplify on this, anything that you can do to reduce the
bandwidth of the digital signal before it's used to modulate the
transmitter will help. One very big advantage is that you can wind down
the bandwidth of the receiver, thus reducing the level of background
noise in the system.


Why did you choose 3MHz?

44,100 X 24 = 1,058,400

1,058,400 bps requires that the frequency of the carrier be at least
2,646,000 Hz. To make it safe, use 3 MHz.

What's the application?

Well, my application was more to do with reception than transmission.

I'd like to know what I would hear on a 3MHz AM carrier whose receiver
[both the AM and the linear PCM part] is at its maximum bandwidth. The
3 Mhz AM receiver is attached to a linear-PCM receiver [once again,
both receivers have the maximum bandwidth possible for them]. The
linear-PCM receiver is attached to a DAC which converts the linear-PCM
signal to analog. This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB.

dB is a ratio, not a power.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Geoffrey S. Mendelson wrote:
wrote:
As a bit of trivia, Reed Solomon encoding was invented without a way to
decode it. That's what you get when you let mathematicians run wild.
For absolutely nothing of any value other than bragging rights, name
the guy who invented the decoding scheme for Reed Solomon. [Hopefully
this isn't wikied someplace. I did one class in grad school on error
detection and correction, and it was a pain in the ass if you get into
the theory. Implementation is quite simple.]

It makes sense. The encoding software had to be ready to put into a probe
before the launch date. Once it was up it could not be changed.

Decoding software was another matter. Since they had years, maybe even decades
to decode the data, and it did not have to be real time, they could continue
to work on it.

All they had to do is not loose the tapes. :-(

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

I'm not sure what you mean by the "probe". The deal with Reed Solomon
is it is a non-binary code, which was a big deal at the time. The
buzzword is Galois mathematics. There wasn't any hardware that could
handle the code when it was invented.

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

On 9/12/06 10:04 PM, in article , "Tim Williams"
wrote:

"Don Bowey" wrote in message
...
There is no such thing as a .00000000001 dB signal

Sure there is. It's very close in amplitude to a 0.0dB signal. ;-)

Tim

Yes Master.... I had a momentary lapse of acumen, but it is clear now. dBm
to the people. :-)

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Michael A. Terrell" wrote in message
...
dB without a reference is meaningless. How can you have a ratio
without a reference?

Easy. "dB" in general usually refers to acoustic power, where the reference
is some ungodly small power level (10^-12W/m^2 IIRC?).

I forget if there's a similar radio context used...

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

The answer is this:

It would be far more suceptable to interference than the AM equivalent.

The far higher bandwidth gives you a far higher noise bandwidth than the
narrower AM equivalent.

So because of the large bandwidth, AM would beat it hands-down.


Sam

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Radium" wrote in message
oups.com...
This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?


I think you need to be a bit clearer in your thinking. I see several people
have commented on your use of dB and it seems Mike dealing with the digital
side so I'll not pick up on those. I'd like to comment on " the antennae
and receivers are so sensitive that they can pick signals as low as........"
and your other comment about wide bandwidth.

Firstly, a "sensitive antenna" isn't a good concept, better to think in
terms of gain.

However, more importantly, sensitivity isn't just about how "small" a signal
your receiver system can "pick up"- you can (in theory) just add more and
more gain. The issue is the ratio of the signal to the noise- that is the
noise your receiver introduces and that which is "picked up" by the antenna.
Winding up the gain doesn't help much with the latter- the noise in the
available bandwith is amplified as well. Often a good way to get a better
signal to noise ratio is to reduce the bandwidth so, before you get too hung
up on having a wide bandwidth, think about what you need to do the job.


I also notice someone mentioned Galois- there was a thread some time back in
uk.radio.amateur where I explained the maths behind these. I'd sure a search
of Google Groups will turn it up.

--
73
Brian
www.g8osn.org.uk

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

On 9/13/06 8:43 AM, in article , "Tim Williams"
wrote:

"Michael A. Terrell" wrote in message
...
dB without a reference is meaningless. How can you have a ratio
without a reference?

Easy. "dB" in general usually refers to acoustic power, where the reference
is some ungodly small power level (10^-12W/m^2 IIRC?).

I forget if there's a similar radio context used...

Tim

There is no exception; dB is meaningless without a reference. Decibel is
used in radio also.

Don

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Tim Williams wrote:

"Michael A. Terrell" wrote in message
...
dB without a reference is meaningless. How can you have a ratio
without a reference?

Easy. "dB" in general usually refers to acoustic power, where the reference
is some ungodly small power level (10^-12W/m^2 IIRC?).

I forget if there's a similar radio context used...


You need to do a lot of studying on how to use the dB. Without a
reference, it is meaningless. The classic use in audio was 1 mW into
600 Ohms = 0 dBm, and yes, there are a number of RF uses for the dB.
Either in reference to one of several different reference levels, or as
an absolute ratio, such as the input to output level of an amplifier.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Samuel Hunt wrote:
The answer is this:

It would be far more suceptable to interference than the AM equivalent.

Including heterodynes?

The far higher bandwidth gives you a far higher noise bandwidth than the
narrower AM equivalent.

So because of the large bandwidth, AM would beat it hands-down.


Sam

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

You got a heterodyne fetish, Radium? There must be some kind of support
group for that.

http://groups.google.co.uk/group/rec...acb45 99d8f13


"Radium" wrote in message
oups.com...
Including heterodynes?

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Brian Reay wrote:
"Radium" wrote in message
oups.com...
This analog signal [which was PCM] is then sent to a
loudspeaker. Just to make things more interesting, the antennae and
receivers are so sensitive that they can pick signals as low as
.00000001 dB. Most likely, what would I hear?


I think you need to be a bit clearer in your thinking. I see several people
have commented on your use of dB and it seems Mike dealing with the digital
side so I'll not pick up on those. I'd like to comment on " the antennae
and receivers are so sensitive that they can pick signals as low as........"
and your other comment about wide bandwidth.



Firstly, a "sensitive antenna" isn't a good concept, better to think in
terms of gain.

Okay, in this theoretical experiment of mine, the gain is set at
maximum thats physically-possible


However, more importantly, sensitivity isn't just about how "small" a signal
your receiver system can "pick up"- you can (in theory) just add more and
more gain.

Okay.

The issue is the ratio of the signal to the noise- that is the
noise your receiver introduces and that which is "picked up" by the antenna.

Winding up the gain doesn't help much with the latter- the noise in the
available bandwith is amplified as well.

Hopefully I can get some frightening-yet-enjoyable heterodynes from far
outer space amplified in my hypothetical audio system.

Often a good way to get a better
signal to noise ratio is to reduce the bandwidth so, before you get too hung
up on having a wide bandwidth, think about what you need to do the job.

Okay.


I also notice someone mentioned Galois- there was a thread some time back in
uk.radio.amateur where I explained the maths behind these. I'd sure a search
of Google Groups will turn it up.

--
73
Brian
www.g8osn.org.uk

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

It would be far more suceptable to interference than the AM equivalent.

Including heterodynes?

Theoretically, with optimal decoding, you require around 3dB C:N to decode
an AM digital signal.

3dB C:N as opposed to the 20dB C:N that you need to get a good AM signal
sounds to be a winner.

But AM would be about 30khz bandwidth, and this PCM signal would be 3mhz.

That means that the bandwidth gives you at least 20dB less sensitivity, so
comparing the signal bandwidth-wise, you only require 0dB C:N across the
same bandwidth to get the AM signal.

So you have a 3dB advantage for conventional AM over PCM.

Next, let us look at the nature of AM and heterodynes.

By the nature of audio AM, you will find that a single heterodyne can
degrade the C:N to as low as 10dB before it becomes perceptible.

So therefore in the same bandwidth with PCM, you then have -10dB C:N, which
is not enough to decode the PCM.

Therefore, PCM is inferior to AM, and you would not only be wasting precious
bandwidth, and face considerable issues with other transmissions and the
physical design of the antenna, transmitters and receivers, you would also
find that it is nowhere near as effective.

Maybe studying something like GSM compression or MP3 compression formats,
FEC and COFDM or similar may be your answer.

COFDM with a good FEC system is one of the most robust methods to transfer
digital data in the presence of heterodynes there is. With the correct
encoding and decoding techniques, you can have easily -80dB C:N because of a
heterodyne some 80dB stronger than your signal, and the data would be still
decoded correctly. Theoretically you could have hetrodynes thousands of dB
stronger than the carrier, but unfortunately the reciever technologies are
nowhere near that advanced yet, but even with cheap decoders, you could aim
for around 80dB as a realistic goal under ideal situations (which is what
you appear to advocate).


Sam
M1FJB

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Michael A. Terrell" wrote in message
...
You need to do a lot of studying on how to use the dB.

I know full well what a logarithm is; don't patronize me.

My point was that some otherwise ambiguous dB scales (at least one) have a
defined absolute basis.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

In article ,
"Tim Williams" wrote:

"Michael A. Terrell" wrote in message
...
You need to do a lot of studying on how to use the dB.

I know full well what a logarithm is; don't patronize me.

My point was that some otherwise ambiguous dB scales (at least one) have a
defined absolute basis.

Like Michael stated dB is a logarithmic reference-less ratio value.

You can use dB for things like amplifiers that have a gain or
attenuators that have a loss for example. The gain of an amplifier can
be expressed in dB because the reference value is the input value of
the amplifier, which will allow you to calculate the output value but
if you are speaking of a value of power or voltage by itself then you
need an absolute scale with a reference quantity.

Absolute scales would be dBV, dBuV, and dBm. In those terms the
reference is 1 volt, 1 micro-volt (0.000001 volt), and 1 milliwatt
(.001 watt).

The reason you need a reference value is noise prevents you from
measuring 0 Volts and 0 watts accurately so you need to use a small
reference value in its place and so everyone agreed to use these
values.

Definitions a
dBV = 20 * log (volts / 1 )
dBuV = 20 * log ( volts / 0.000001 )
dBm = 10 * log ( power / .001 )

So for example:
30 dBm = 1.0 watt
0 dBm = 0.001 watt (the reference value)
-30 dBm = 0.000001 watt

Most of the time in radio dBm, dBuV, and watts are used.

--
Telamon
Ventura, California

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Tim Williams wrote:

"Michael A. Terrell" wrote in message
...
You need to do a lot of studying on how to use the dB.

I know full well what a logarithm is; don't patronize me.

My point was that some otherwise ambiguous dB scales (at least one) have a
defined absolute basis.


I'm not "Patronizing" you. You were using it in the wrong context.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Telamon" wrote in message
...
Absolute scales would be dBV, dBuV, and dBm. In those terms the
reference is 1 volt, 1 micro-volt (0.000001 volt), and 1 milliwatt
(.001 watt).

The reason you need a reference value is noise prevents you from
measuring 0 Volts and 0 watts accurately so you need to use a small
reference value in its place and so everyone agreed to use these
values.

Given you are discussing use of the dB, I think the above leaves a bit out.
You can't use 0W as your reference because, given the definition of the dB,
you'd need to divide by 0 which, as I'm sure you know, isn't acceptable.

--
73
Brian
www.g8osn.org.uk

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

On 2006-09-13, Don Bowey wrote:
On 9/12/06 3:57 PM, in article
, "Radium"
wrote:


In fringe areas, analog cell phones could be well understood despite the
poor signal-to-noise ratio. Digital cell phones in a fringe area just quit
working, or lose sync and you hear bits of other conversations.


with GSM phones I got a "guitar sounding" effect in marginal areas

Bye.
Jasen

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

On 2006-09-13, Radium wrote:


Easy for you to ask. I doubt any store has the device. And the
equipment required to amplify .00000000001 dB to an audible level would
take up the entire room.


There is no such thing as a .00000000001 dB signal

Whats stops a .00000000001 dB signal from existing?

Nothing, it's just indistinguishable from a 0db signal.

In other words it's about half the amplitide of a 3db signal...

It's a logarythmic scale.

Bye.
Jasen

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

jasen wrote:

On 2006-09-13, Radium wrote:

Easy for you to ask. I doubt any store has the device. And the
equipment required to amplify .00000000001 dB to an audible level would
take up the entire room.


There is no such thing as a .00000000001 dB signal

Whats stops a .00000000001 dB signal from existing?

Nothing, it's just indistinguishable from a 0db signal.

In other words it's about half the amplitide of a 3db signal...

It's a logarythmic scale.

Bye.
Jasen


No, without a reference, its use is meaningless. He was trying to
use dB for an absolute signal level, not a ratio.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

"Telamon" wrote in message
...
My point was that some otherwise ambiguous dB scales (at least one) have
a
defined absolute basis.

Like Michael stated dB is a logarithmic reference-less ratio value.

So what is acoustic dB?
http://home.new.rr.com/trumpetb/audio/dBexamp.html
SPL, I should say.

There it lies, x dB on the left scale.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Tim Williams wrote:

"Telamon" wrote in message
...
My point was that some otherwise ambiguous dB scales (at least one) have
a
defined absolute basis.

Like Michael stated dB is a logarithmic reference-less ratio value.

So what is acoustic dB?
http://home.new.rr.com/trumpetb/audio/dBexamp.html
SPL, I should say.

There it lies, x dB on the left scale.


That is a SPL chart with the dB levels referenced to 0 dB SPL =
0.0002 µbar.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
 

Tim Williams wrote:

"Telamon" wrote in message
...
My point was that some otherwise ambiguous dB scales (at least one) have
a
defined absolute basis.

Like Michael stated dB is a logarithmic reference-less ratio value.

So what is acoustic dB?
http://home.new.rr.com/trumpetb/audio/dBexamp.html
SPL, I should say.

There it lies, x dB on the left scale.


Read this Sound Level Meter manual if you want to understand that
chart.

http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/3304050_PM_EN.pdf


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida