Continuing on the #fieldtelephone and also #barbedwirefencephone journey, I got two actual field telephones last weekend 🥳 (yes, finally, and only now 🙈)
Time to test a few things!
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One thing I was interested in is connecting a normal phone to the field telephone. The ringing generator in the field telephone will make the normal phone ring. That’s pretty neat. Talking to each other like that is not possible however, not enough power it seems. Didn’t get deeper into that last night though
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Next up, can my DIY ringing generator make the field telephone ring? Well, kind of. It rings but only very faintly. I realized afterwards that I was probably running the circuit at 9V only, 12V may have been more suitable. Yet another thing to try next time.
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For reference, this is what they normally sound like when ringing (really glad I got two to test this out)
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Did some more experimentation today. Like hooking up the #fieldtelephone to the barbed wire fence phone experiment. And while we were able to talk while the FT was in OB mode, it wouldn’t work while in ZB mode. And even after looking at the schematic for half an hour still don’t quite understand while.
Also didn’t take any pictures today, which kind of bugs me 😑
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@tiefpunkt for ZB you will need the central battery voltage across the fence, preferably with some coils between it and the line (so the audio signal doesn't disappear in the battery/power supply) or a capacitor across the battery (maybe 100nF?) to let the AC audio signal through. Central battery voltage in telephone exchanges can be -24 to -60V DC (maybe -12V might work, but -24V would be better for short distances to the normal telephone).
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@tiefpunkt some years ago I built a system to simulate a phone line to demonstrate how room audio from phones was backfed as a surveillance method (widespread in East Germany but possible in other countries), and my "telephone line" used a 24V power supply..
https://www.youtube.com/watch?v=gcq7_JG6oGQ
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@vfrmedia thank you, I'll take a look at that. We did have 12V on the "fence" (replicating https://social.tchncs.de/@tiefpunkt/113783545007454792 essentially), but maybe that just wasn't enough, or missing the inductors. Worth another try next week :)
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