Jeff Liebermann wrote:
Argh, that brings back fond nightmares of Ma Bell.

And of splicing damaged buried plant in a wet trench...that stuff had a
bite to it.

On 6/30/07 10:44 PM, in article
et, "DTC"
wrote:

Mike Kaliski wrote:
ELF communications are carried out at very slow data rates, only a few
characters per hour at best.

Actually its on the order of several characters per minute using a 64
character "alphabet".

It is possible to communicate at a base band frequency of 0Hz. This is what
happens when you talk down a hard wired telephone or intercom. At a
telephone exchange (switching centre), the signals from each line are
modulated onto a higher frequency for onward transmission down a trunk wire
cable or fibre optic cable. The multiplexed high frequency modulated signals
are down converted back to audio frequencies once they reach the intended
destination.

In the old T carrier (before 24 channel digital T1) carrier, each telephone
conversation was modulated onto a low frequency radio frequency AM signal
ranging from (and don't quote me as its been over thirty years since I
worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide
AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band.

The O Carrier systems went from a low of about 32 kHz up to 164 kHz if I
remember right. And the mainstay of long-haul communications (L Carrier)
channel bank, was 64 - 108 kHz.

One of the most strange Carrier Systems I worked with was a 1930s vintage H
Carrier, one channel ssb "system" operating at about 12 kHz, and it ran
without automatic synchronization. That was in the 60s. We used it as a
maintenance channel in a voice over data configuration for a gap-filler
radar site. I've never seen a more extreme merging of old and new
technologies.

Don

On 6/30/07 11:25 PM, in article , "John Smith
I" wrote:

Radium wrote:
...

You miss the simple point, the dc is the carrier ... instead of dc, you
could put a 1 hz signal on the line and modulate it with your voice,
indeed, you can put a 30 hz signal on the line and modulate it with your
voice--if you can tollerate a bad 30 hz hum! But, who knows, perhaps
you are tone deaf to the 30 hz hum and would like it ...

JS

But you miss the basic point......

The topic was Amplitude Modulation.

On 6/30/07 11:27 PM, in article , "John Smith
I" wrote:

Don Bowey wrote:

...

You are an idiot ... bother some one who has the time to take you to
task ...


Open your mind.

On Jun 30, 2:55 pm, John Smith I wrote:
Radium wrote:

...

I am getting conflicting answers. Some say it's possible to modulate a
carrier frequency at a frequency higher than the carrier frequency,
others say it isn't.

Who is right?

Radium:

Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice),
(hint, your telephone line is an example) right?

However, when you get into RF--possible, usable, desirable are seperate
and distinct things.

Again, with simple logic, modulating a 30 CPS signal with limited voice
freq (say 5K wide) is going to create a LOT of harmonics and mixed
signals, ain't it? Suggesting a very wide band receiver would be needed
to begin with ... in my humble opinion, and for various reasons, NO, it
is NOT possible ...

Regards,
JS

radium, I applaud you in your interest generating discussion.

if there are no questions there are no answers; dumb or smart!

to me your questions came across wonderfully, and generated both
responses.

as humans we stand on two legs, most of us that is.

men get the honor and privilage to stand on three legs from time to
time.

this is our blessing and our curse!

ps. how would u like to change the cell phone industry? and your
discussion group of course!

remeber all things are possible!!!!!!!!!!!!!!!!

Don Bowey wrote:

Open your mind.


Geesh!

Hook up a 20X linear behind an xmitter and see if you can't find some
artifacts ...

JS

DTC wrote:
Jeff Liebermann wrote:
Argh, that brings back fond nightmares of Ma Bell.

And of splicing damaged buried plant in a wet trench...that stuff had a
bite to it.

The Coax we used for the repeaters was fed with 250-0-250V DC and the
current was regulated at 49mA. The only time the cable jointers worked
on it the power feed was disabled.

On 7/1/07 8:05 AM, in article , "John Smith I"
wrote:

Don Bowey wrote:

Open your mind.


Geesh!

Hook up a 20X linear behind an xmitter and see if you can't find some
artifacts ...

JS

Sheesh....

That has nothing to do with helping someone understand AM. It appears you
are more interested in dumping your blog on this board, than providing
something to clarify the real answers for an electronic novice.

On 7/1/07 8:05 AM, in article , "John Smith I"
wrote:

Don Bowey wrote:

Open your mind.


Geesh!

Hook up a 20X linear behind an xmitter and see if you can't find some
artifacts ...

JS

By the way, I have. A 10B to a GPT750.

Don Bowey wrote:

That has nothing to do with helping someone understand AM. It appears you
are more interested in dumping your blog on this board, than providing
something to clarify the real answers for an electronic novice.

So, you will decide what he needs to know and what he doesn't?

If he becomes aware of the more esoteric and trivial it is dangerous.

Get real control freak!

JS