I came up with that idea over 20 years ago when we needed an "Advertiser Radio" to park up the road near the Interstate, with a Digital Voice Recorder (DVR, or Watergate) and a prerecorded message advertising our shop. I used a 555 timer circuit set to fire the DVR about every 10 minutes or so, and the radio, a Cobra 25 LTD, which was set in TX the whole time (shorted jumpered mic plug), although I may have had the 555 trip the DVR, which in turn would key the radio, I can not remember that particular detail. In between message firings, there would be no carrier, or maybe just enough signal to hear from 5 feet away.
This works on Cobra 29 style radios too, pull JP32 and feed the voltage into the left trace that JP32 was connected to, to do the same thing.
This can have the "windshield wiper effect" on receivers on the other end, with the carrier dropping low in between words.
Now, mind you, I have not worked in a CB shop in purt dern near 20 years, though, so this is all from memory. I used to work in a shop in North East Ohio, near Youngstown.
I used to make DVR's from ISD chips, chipcorders like Memo Mate key fobs, and other such. I still have a few samples of the dead bug style o9nes I had made, I even used sound toy boards I retrofitted with the record and other such functions of the chips.
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