Sunday, September 19, 2010

Car radio PTO

Funny thing, this past week I read at some blog (can't recall which one) something about an old car radio tuner using an unusual PTO mechanism, yesterday I went to a friend's house and he wanted to get rid of some electronics junk (i.e: ham gold), end up with this car radio:

Can you see the PTO? Well, as soon as I have some time will let you know what it can be done, maybe an 50Mhz receiver or another 144...who knows.

From what I could see the schematic is similar to some old designs using extensively IF cans, there's a nice tutorial in the following link about those designs:

I was given another radio but more modern design, anyhow one of the 10.7 Mhz crystal filter that came in it is already at the VHF receiver replacing the 10.7 Mhz simple crystal.

I am still having some trouble in the receiver, pressing the board and there's some interference and loss of signal, probably some solder joint that I didn't found yet. I am also in the process of adding an s-meter to the MC3361. Will post design as soon as it works....

Today while I was doing some tests, and with a piece of wire (70cm) inside the shack, I got some, of what looks like, meteo sat transmission! Incredible!
Here's the short video of NOAA 18 at 137.100 Mhz today:



Anonymous said...

the FM front-end is similar to the above, but it's not exactly the same, or it is? the one I'm showing uses tuning voltage for the FM broadcast band and permeability (I guess?) tuning for LW/MW.

Anonymous said...

anyway I'm kinda confused by the photo.. the early VHF FM FE shown on Vintage Radio is tuned by coils, but the IF shows SIP ICs, that would suggest more modern FE with varicap tuning. :-)

Ricardo - CT2GQV said...

The blog I refer my comments is another one but your link looks exactly the mechanical part I have. Still didn't disassembled it completely to figure out how it works. I don't think tuning voltage is used for FM, looks more an oscillator for mixing with a tracking front end, my guess of course.

Ricardo - CT2GQV said...

My radio has some SIP IC's but I think their for audio and for FM at 10.7Mhz