Cheap AM chips
 

Hi All;

I just bought 75 LM3820 chips from B.G. Micro for 12 cents each. You have to buy tubes of 25 chips. The chips seem to work great, I'm using one yellow IF can from a pocket radio, and two 455khz ceramic filters in the IF. I used an FET detector stage, and there's enough audio level to drive the line input of a boom box that I was using for a quickie amp. I don't know what the upper limit is of the oscillator, but I had it up to 13 mhz with no trouble, at least after I figured out the scope probe was loading down the oscillator, and stopping it at 5 mhz.

The pin out in the original data sheet for the LM3820 seems incorret, or maybe just confusing. I couldn't get those configurations to work. I had an app guide for the LM1868, which was using the LM3820 for the AM side of an AM/FM system. Those connections shown were considerably different from the LM3820 data sheet, and it works! Both data sheets show a tuned RF input circuit, but I'm using just a six foot wire, and it works ok on AM.
I'm using voltage tuning, using the NTE618 as the capacitor in the AM oscillator. I haven't tried it on short wave yet, that's tomorrow's project. I mainly want the 39 to 31 bands, but may play with using it on the HF ham bands.

I can e-mail the schematic if anyone is interested, it might be easier to follow than the data sheet. It's an old chip, but the price, and ease of use attracted me to it.

Frank

Cheap AM chips
 

Frank wrote:

Hi All;

I just bought 75 LM3820 chips from B.G. Micro for 12 cents each. You
have to buy tubes of 25 chips. The chips seem to work great, I'm using
one yellow IF can from a pocket radio, and two 455khz ceramic filters
in the IF. I used an FET detector stage, and there's enough audio level
to drive the line input of a boom box that I was using for a quickie
amp. I don't know what the upper limit is of the oscillator, but I had
it up to 13 mhz with no trouble, at least after I figured out the scope
probe was loading down the oscillator, and stopping it at 5 mhz.

The pin out in the original data sheet for the LM3820 seems incorret,
or maybe just confusing. I couldn't get those configurations to work. I
had an app guide for the LM1868, which was using the LM3820 for the AM
side of an AM/FM system. Those connections shown were considerably
different from the LM3820 data sheet, and it works! Both data sheets
show a tuned RF input circuit, but I'm using just a six foot wire, and
it works ok on AM.
I'm using voltage tuning, using the NTE618 as the capacitor in the AM
oscillator. I haven't tried it on short wave yet, that's tomorrow's
project. I mainly want the 39 to 31 bands, but may play with using it
on the HF ham bands.

I can e-mail the schematic if anyone is interested, it might be easier
to follow than the data sheet. It's an old chip, but the price, and ease
of use attracted me to it.

Schematic please! Thanks

Bob WB0POQ

Got an address to e-mail it to? Mine's

I couldn't figure out how to send an E-mail off the forum, if you send amy an e-mail, I think by clicking on my nmame here, I can send a schematic.

Frank