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Fictional "Intercom System" Over City Power Lines
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 14, 2006 4:36 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

phaeton wrote:
Quote:


It could have been used in a secure area for non secure
communications, but not anywhere near combat zones where targeting
information and troop movements were discussed. Also, there was little,
or no electrical grid in those zones, so you didn't have to worry about
20/50/60 Hz hum on the receiving end. There are places that you could
have enough AC ground currents to completely swamp this type of
communications.


--

That's what I'd figure. Although, the typical field phone is usually
radio, i presume. I'm sure that modern field phones use encryption and
frequency hopping and stuff, but I bet the phones used in WWII probably
had absolutely no scrambling/descrambling capability.


Field phones are used where you are in a fixed location for a while.
radios are used when you have to keep moving. If you every looked at an
old field phone you would see how simple, and how rugged they were.


--
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
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phaeton
electronics forum Guru Wannabe


Joined: 02 May 2005
Posts: 112

PostPosted: Fri Jul 14, 2006 3:13 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

Quote:

It could have been used in a secure area for non secure
communications, but not anywhere near combat zones where targeting
information and troop movements were discussed. Also, there was little,
or no electrical grid in those zones, so you didn't have to worry about
20/50/60 Hz hum on the receiving end. There are places that you could
have enough AC ground currents to completely swamp this type of
communications.


--

That's what I'd figure. Although, the typical field phone is usually
radio, i presume. I'm sure that modern field phones use encryption and
frequency hopping and stuff, but I bet the phones used in WWII probably
had absolutely no scrambling/descrambling capability.
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 14, 2006 1:18 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

Michael Black wrote:
Quote:

Yeah. The field telephone for GI Joe (the action figure) came with a roll
of wire.

I gather the system of driving rods into the earth and using them to
communicate appeared frequently(?) during WWII in the hobby publications,
in that it was something one could experiment and play with while radio
was out of the picture. QSTs from the period likely would offer up
an article or two.

Electronics Illustrated in the sixties ran an article about it,
and the image I remember is of a drawing with a telephone handset.
That certainly conjures up an image of a "field phone".

Michael


It could have been used in a secure area for non secure
communications, but not anywhere near combat zones where targeting
information and troop movements were discussed. Also, there was little,
or no electrical grid in those zones, so you didn't have to worry about
20/50/60 Hz hum on the receiving end. There are places that you could
have enough AC ground currents to completely swamp this type of
communications.


--
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
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Michael Black
electronics forum Guru Wannabe


Joined: 24 Mar 2005
Posts: 251

PostPosted: Thu Jul 13, 2006 6:08 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

"Michael A. Terrell" (mike.terrell@earthlink.net) writes:
Quote:
jasen wrote:

On 2006-07-12, phaeton <blahbleh666@hotmail.com> wrote:


Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John

Interesting. I'm going to have to try that.

It's called a field telephone. you might be able to get a pair at a surplus
store (probably they've all gone to collectors).


Real field phones used two conductor cable, usually made with steel
wire so it wasn't easy to cut or break. Using the ground to carry the
signal would allow the enemy to monitor your communications. they had a
hand crank generator to signal other phones on the line, and even
portable switchboards for command locations.

Yeah. The field telephone for GI Joe (the action figure) came with a roll

of wire.

I gather the system of driving rods into the earth and using them to
communicate appeared frequently(?) during WWII in the hobby publications,
in that it was something one could experiment and play with while radio
was out of the picture. QSTs from the period likely would offer up
an article or two.

Electronics Illustrated in the sixties ran an article about it,
and the image I remember is of a drawing with a telephone handset.
That certainly conjures up an image of a "field phone".

Michael
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Thu Jul 13, 2006 5:38 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

jasen wrote:
Quote:

On 2006-07-12, phaeton <blahbleh666@hotmail.com> wrote:


Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John

Interesting. I'm going to have to try that.

It's called a field telephone. you might be able to get a pair at a surplus
store (probably they've all gone to collectors).


Real field phones used two conductor cable, usually made with steel
wire so it wasn't easy to cut or break. Using the ground to carry the
signal would allow the enemy to monitor your communications. they had a
hand crank generator to signal other phones on the line, and even
portable switchboards for command locations.


Quote:
What kind of wattage power amp

more is better, a step-up transformer on the output may help too.

, how far is a goodly distance,

more than 10 times the electrode separation. should be possible.
possibly much more.

and wouldn't the dirt also be full of all kinds of other electrical 'noise'
in this case?

depends on the territory.

Oh yeah, and do I need decoupling caps on the output and
input of the amps?

could help.

Bye.
Jasen


--
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
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John Popelish
electronics forum Guru


Joined: 29 Apr 2005
Posts: 1601

PostPosted: Thu Jul 13, 2006 4:55 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

phaeton wrote:
Quote:
Ok...

Dumb question time- Need I put both + (signal) and - (ground) into
the dirt for both sending and receiving end?

I found some 6 penny nails and crimpable wire connectors to use as
electrodes, but it was thunderstorming pretty heavily last night, so no
go. I have both some TDA2002vs and LM383 amplifiers (~7W) that I could
try out for this. (I have a small yard, so....)

You need something like 4 foot or longer ground rods at opposite
corners of your property (if you want any hope of getting the signal
beyond your own yard), and a step up isolation transformer (something
like a tube amplifier output transformer, or line to speaker
transformer) connected backwards (to step the voltage up) to get a
fair impedance match to the resistance between the rods and to
eliminate any ground loop current caused by the instantaneous
difference between the ground potential at the rods and that at your
amplifier.

You can drive the transformer with an ordinary speaker output from any
amplifier.
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phaeton
electronics forum Guru Wannabe


Joined: 02 May 2005
Posts: 112

PostPosted: Thu Jul 13, 2006 4:45 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

Ok...

Dumb question time- Need I put both + (signal) and - (ground) into
the dirt for both sending and receiving end?

I found some 6 penny nails and crimpable wire connectors to use as
electrodes, but it was thunderstorming pretty heavily last night, so no
go. I have both some TDA2002vs and LM383 amplifiers (~7W) that I could
try out for this. (I have a small yard, so....)


Thanks!

-phaeton
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jasen
electronics forum Guru Wannabe


Joined: 18 Jun 2006
Posts: 204

PostPosted: Thu Jul 13, 2006 11:12 am    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

On 2006-07-12, phaeton <blahbleh666@hotmail.com> wrote:
Quote:


Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John

Interesting. I'm going to have to try that.

It's called a field telephone. you might be able to get a pair at a surplus
store (probably they've all gone to collectors).

Quote:
What kind of wattage power amp

more is better, a step-up transformer on the output may help too.

Quote:
, how far is a goodly distance,

more than 10 times the electrode separation. should be possible.
possibly much more.

Quote:
and wouldn't the dirt also be full of all kinds of other electrical 'noise'
in this case?

depends on the territory.

Quote:
Oh yeah, and do I need decoupling caps on the output and
input of the amps?

could help.

Bye.
Jasen
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John Larkin
electronics forum Guru


Joined: 29 Apr 2005
Posts: 4320

PostPosted: Thu Jul 13, 2006 2:34 am    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

On 12 Jul 2006 11:47:47 -0700, "phaeton" <blahbleh666@hotmail.com>
wrote:

Quote:


Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John

Interesting. I'm going to have to try that.

What kind of wattage power amp,

As much as you can get.

Quote:
how far is a goodly distance,

I've heard of a mile or two.

Quote:
and
wouldn't the dirt also be full of all kinds of other electrical 'noise'
in this case?

Yup, some worthless and some interesting.


Quote:
Oh yeah, and do I need decoupling caps on the output and
input of the amps?


No.


John
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phaeton
electronics forum Guru Wannabe


Joined: 02 May 2005
Posts: 112

PostPosted: Wed Jul 12, 2006 6:47 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

Quote:

Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John

Interesting. I'm going to have to try that.

What kind of wattage power amp, how far is a goodly distance, and
wouldn't the dirt also be full of all kinds of other electrical 'noise'
in this case? Oh yeah, and do I need decoupling caps on the output and
input of the amps?

:-D

-phaeton
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John Larkin
electronics forum Guru


Joined: 29 Apr 2005
Posts: 4320

PostPosted: Wed Jul 12, 2006 6:42 pm    Post subject: Re: Fictional "Intercom System" Over City Power Lines Reply with quote

On 12 Jul 2006 09:13:35 -0700, "phaeton" <blahbleh666@hotmail.com>
wrote:

Quote:
You guys all read books like "The Mad Scientist's Club" when you were
kids, right?


I recall that in this book they (the pre-adolescent boys in the Mad
Scientists Club) devised (among many other things) an intercom system
that allowed them all to communicate from house to house across a small
town, using its power grid.

I know there are in-house (room to room) intercom kits that you can
buy, and they work with some success, but is it possible on this scale?
Not that i'd try it, mind you. I suppose there are a lot of obstacles,
i.e. having to filter out a 60hz AC hum with a huge amplitude, for
starters. You'd be limited to AM instead of FM, I presume, blah blah.

I realize that it is a fictional book and it has a lot of, shall we say
"embellishments" for the sake of the story. For instance, they often
used lots of radio equipment, and while nothing seemed to have antennas
on it, nobody ever mentioned line-of-sight, signal gain, pine trees,
radio control frequencies vs. ham radio frequencies, the FCC or the
usual stuff, most everything had a perfect 5+ mile range. Maybe the
RF situation in the sky was different in the 1960s, eh?

I had completely forgotten about this 'intercom system' i read about 20
years ago, until I overheard (yet another) discussion about the
"broadband over powerlines" concept that people have been debating the
last few years.


For what it's worth, I remember that book fondly in my youth, and
lately I've been developing a small (but present) interest in
communications using unconventional means.

/lameness
-phaeton

Power lines would be tough. You can use dirt instead. Just bury a pair
of electrodes as far apart as possible and drive with a power amp,
receive with any sensitive audio amp. Party-line commiunications are
possible across goodly distances.

John
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phaeton
electronics forum Guru Wannabe


Joined: 02 May 2005
Posts: 112

PostPosted: Wed Jul 12, 2006 4:13 pm    Post subject: Fictional "Intercom System" Over City Power Lines Reply with quote

You guys all read books like "The Mad Scientist's Club" when you were
kids, right?


I recall that in this book they (the pre-adolescent boys in the Mad
Scientists Club) devised (among many other things) an intercom system
that allowed them all to communicate from house to house across a small
town, using its power grid.

I know there are in-house (room to room) intercom kits that you can
buy, and they work with some success, but is it possible on this scale?
Not that i'd try it, mind you. I suppose there are a lot of obstacles,
i.e. having to filter out a 60hz AC hum with a huge amplitude, for
starters. You'd be limited to AM instead of FM, I presume, blah blah.

I realize that it is a fictional book and it has a lot of, shall we say
"embellishments" for the sake of the story. For instance, they often
used lots of radio equipment, and while nothing seemed to have antennas
on it, nobody ever mentioned line-of-sight, signal gain, pine trees,
radio control frequencies vs. ham radio frequencies, the FCC or the
usual stuff, most everything had a perfect 5+ mile range. Maybe the
RF situation in the sky was different in the 1960s, eh?

I had completely forgotten about this 'intercom system' i read about 20
years ago, until I overheard (yet another) discussion about the
"broadband over powerlines" concept that people have been debating the
last few years.


For what it's worth, I remember that book fondly in my youth, and
lately I've been developing a small (but present) interest in
communications using unconventional means.

</lameness>
-phaeton
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