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Old 19th Feb 2018, 9:39 am   #5
Dave Moll
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Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,127
Default Re: Phones or intercoms

Yes, these generally operate as intercoms and are powered by local batteries. They are not suitable for connecting to the telephone network!

When "off-hook", pressing the ring button simply places the battery across the line, ringing the DC bell (which is connected across the line when "on-hook") of the remote unit.

When both units are off-hook, it would appear that it uses a simple series connection between the transmitters and receivers.
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