Ok, Makers it’s time for another adventure in electronics with Carl & Jerry. In this short story the local police need Carl & Jerry’s help rescuing a kidnapped girl (back in the 50’s junior sleuths and electronic wizards solved most crimes & mysteries in clever ways). The kids need to figure out a way to listen in on the kidnapper’s scheduled phone call without said kidnapped knowing he’s being listened to… Carl & Jerry, along with a cop dressed up as a milkman save the day…
“It’s not impossible,” Jerry interrupted, “but I wish we had more time. I guess we’ll have to use an inductive type bug. This is really just a large inductance placed somewhere near the telephone induction coil. The field about that coil induces faint currents in our inductance that can be amplified until they are audible.”
“What do you mean by ‘near?’ ” the chief asked.
“Well, a large coil is supposed to be able to pick up conversations ten feet from the telephone; but I’ll feel safer if we can place our bug five or six feet away.”
“Do you have such an inductance?”
“Nope, but Carl and I can make one in shop class at school this afternoon. Really it’s just a couple of pounds of very fine wire, say #40, wound on an iron core, This inductance could feed an amplifier~modulator that would modulate a small transmitter. That would allow the gadget to be placed near the telephone without any wires going to it. We could listen some distance away. The only trick is to place the bug close to the telephone the parent uses without arousing his suspicion or the suspicion of anyone watching him.”
January 1959 V10-1 Little “Bug” with Big Ears – Link.
What are the “Carl & Jerry – Adventure in electronics”? In the 50’s and 60’s John T. Frye, W9EGV / Popular Electronics published a series of fiction stories called “The Carl and Jerry stories” – In each story the pair acquired new skills, got their ham radio licenses and used their knowledge of electronics to get out of a jam or solve a mystery – there isn’t a complete collection of all the stories that I know of, but there are some scans / text online. If you have more of these or know where more can be found, let me know.