Does anyone remember the "Rock Bender" project for crystal scanners?

[Omega-TI]

Back in the late 1970's or early 1980's, I remember reading about, "The Rock Bender". It was a project that allowed one to sort of "tune" a crystal scanner by doing something with the crystal. If I remember right it had a schematic diagram and construction instructions. I don't remember if it was in Radio-Electronics, Popular Electronics, or one of the many other magazines I used to buy. I'd like to find it again just to see if it would make a nice project to play with this summer, just for kicks. Does anyone else remember it?

 

[ko6jw_2]

A small trimmer capacitor across the crystal will enable it to be"netted" to the exact frequency by metering off the discriminator tap. There were some very early scanners that had this feature (don't remember which). Also, commercial receivers had this feature. I have an old GE monitor receiver that was designed for use as an alerting receiver in fire stations that has these. I was able to skew a crystal for 154.445 MHz down to 154.430 MHz once. I don't know how far it could have been tuned (not very far I assume). The main problem I see with trying to add this capability to an existing scanner is space on the board. I can see adding one capacitor to one crystal but there would not be room for more that one. The capacitors in the GE receiver are ceramic trimmers of a few pf.

 

[cmaness2001]

I've been using one of these Si5351 signal generators on an old crystal scanner. I tune it to the fundamental of the crystal I need. It actually works pretty well, fun to play around with. If I were a younger man I would reprogram the controller on it to allow for direct entry of the receive frequency...

 

[IC-R20]

I've been using one of these Si5351 signal generators on an old crystal scanner. I tune it to the fundamental of the crystal I need. It actually works pretty well, fun to play around with. If I were a younger man I would reprogram the controller on it to allow for direct entry of the receive frequency...


View attachment 166579

Pretty cool. Back in 2016 someone was showing me something like that they used on their HF transceiver. Through a lot of spurs when transmitting but was no worse than a Baofeng does on vhf.