any idea about power line intercom?

[haylin1217]

i need some backgrounds and theories about power line intercom as my reference for a certain project study.

could anyone give some ideas?

any help would be appreciated. thanks.

 

[audioguru]

I think power line intercoms used FM about 30 years ago.

 

[MrAl]

i need some backgrounds and theories about power line intercom as my reference for a certain project study.

could anyone give some ideas?

any help would be appreciated. thanks.

Hi there,

If you read audioguru's post and still want to proceed, then you
might want to do a search on this site. We talked about this quite
a bit not that long ago, maybe a year or less.
This subject seems to come up now and then.

The basic idea is to inject a relatively high frequency modulated wave into the line,
like around 250kHz or even higher, then demodulate it on the receiver end to recover
the original signal.
It's basically like a radio only at lower frequency and the line acts sort of like an antenna.
The frequency is kept high so that a filter on the receive end can separate it easily apart from
the constant 50 or 60Hz line frequency who's amplitude is much much higher.

 

[haylin1217]

thank you for replying audioguru and Mral. I am still in the progress of researching about power line intercoms. I hope I could still get some ideas from you.

I am just wondering if the signals that I would like to inject to the main power ac line would not be seen as a disturbance or noise riding on the 50-60 Hz power line.

I am still in the learning process on this thing so just please correct me if I'm wrong.

thanks for the help.

 

[audioguru]

A power line voltage is 120V or 240V.
The signal level from your intercom is only 1V or less so it will not cause interference to the power line voltage.

But a power line is very noisy due to light dimmers and switching power supplies.
Therefore the intercom should use ultrasonic FM for good noise rejection.

 

[haylin1217]

power line intercom again..

what are the standards and protocols needed to consider in building power line intercoms?

thanks in advance....

 

[audioguru]

Power line intercoms were made and discontinued a long time ago.

 

[marcbarker]

what are the standards and protocols needed to consider in building power line intercoms?

You'd probably want to study the characteristics of typical mains wiring at RF frequencies, i.e. what kind of 'transmission line' properties it has. It's probably a '50 ohm feeder cable' above a few 100 kHz. Then from there it's like any other radio signalling project. Only protocols and standards I think apply are HV safety and common sense around lethal voltage. I think you have a blank sheet to start with here... Post a schematic and the people here will review it!

 

[john1]

Hi,

I recall seeing one a long time ago.
I think it was AM at quite a moderate frequency, guessing it was below long wave frequencies. I think the injected signal was quite small, such that the receiver had to have reception gain similar to a radio.
I dont think it carried past the local substation which made it quite localised.
Dont recall if the signal carried onto the other phases, it may have done.

I have a feeling that the (UK) electricity companies did not approve of these units and may have 'prohibited' them, but i dont think they were ever made illegal.

John