25 March 2011

Fiddling with a MC145106 PLL

While re-arranging the shack, I have come across a 10-11m RTX with MC145106 PLL inside. I had used it on 10m, so I decided to check its electrolytic capacitors since it was built more than 20 years ago. While peeking inside I traced damages and mods I had done and fixed, and that was about 20 years ago too!

I had always wanted to "upgrade" the RTX by feeding the PLL divider with a binary counter, in place of the rotary switch + band switches. Now that I can "master" (aehm...) microcontrollers, adding such a control will give even more flexibility.

The plan is to remove the two 4008 adders between the rotary switch and the PLL, and replace them with DIP sockets. Then build a daughter board with a ATtiny2313 and two or more buttons to get the tuning done.

If this works, meaning that I have understood how was designed the PLL circuitry, an external display could be added too, memories, scanning, restricting to 10m and so on.

The RTX will keep the orignal 10 kHz channelization, unless I manage to make the PLL chip do 5 kHz increments. But that would require close work on the PLL.

First I will check the RTX power ups and is still generating some RF :-)

The picture shows PCB traces between 2x4008 and the PLL 145106.

For the records, this RTX is called Pearce Simpson Super Cheetah but it has 6 "bands". It has a circuit very similar to Superstar 3900, which I am using as a reference for this mod.