Cheap AM radio chips!
 

I just bought 75 LM3820 AM radio chips from B.G Micro at 12 cents each. The chips have some wierd Delco number on them, but they are the LM3820's. You have to buy them by the tube , 25 per tube for 3 bucks! It looks like by using other oscillator configurations, you can cover some short wave. I don't know how high the oscillator will run yet, but I had it up to 5 mhz last night using a ferrite antenna core for the coil core from a newer pocket radio. It had 30 turns of #28 for the primary, and 6 turns of #24 hook up wire of the secondary. With an MVAM108 diode, I could tune from about 2.5 mhz to 5 mhz. I'm in the process of making a couple other coils, one for AM starting with 60 turns, and another for short wave coverage up to 10mhz on a smaller core starting with 70 turns (cuz that's what fit on the core). The coils I'm using are larger, and will probably need shielding. Aluminum shields kill the oscillation, but brass works ok. I'll be using an FET detector satge, and I'll add a BFO for sSSB, and CW, and LM386, to start with, for audio.

I tried using a Red AM oscillator can, but it doesn't have enough range. I'm using varactor diodes for tuning. A black IF can with the capacitor removed has almost enough coverage.

I'm using the diagram from App note AN-147 as a guide to connetions of the chip. I do have the data sheet as well.
Frank

Crap, can't get them run abouve 5 mhz! But they should still be useful.

Frank

Wait, the scope wasn't seeing the signal, or shorting out the higher freq. They do run well into the shortwave range. I had one up to 13 mhz with no problem using junk box parts, an dthe scope probe set to X10, Doh!

Frank