The AM Forum

Here’s another project that I’m working on. I’m challenging myself to build things smaller. This idea I’m trying to fit in a 1.75” x 1.75” plastic container that I bought from the Container Store.

It’s powered from a small A23 12v battery. The direct conversion receiver uses an SA612 chip and an LM386 audio amp. The antenna transformer is wound on a Starbucks straw, but I could only fit enough turns for 11.5uh. It still should do ok.

Now, we can discreetly listen to 3870 KHz in the club without spooking the chics.

Jon

If you would like to build an All-Band receiver sometime check out the Silicon Labs
Si473X series;

https://www.silabs.com/documents/public/data-sheets/Si4730-31-34-35-D60.pdf


Phil - AC0OB

Could one add a BFO for CW? Does not look like it to me.
Thanks
Carl

The purpose is for a fun AM project, not CW.

Jon

My question was more hypothetical and technical, not having worked with either of the chips discussed
Carl

No problem. I’m sensitive to people pointing out my overuse of CW. I have built class E rigs, you know... 😉

Jon

Phil - AC0OB
[/quote]
Could one add a BFO for CW? Does not look like it to me.
Thanks
Carl
[/quote]

A direct conversion does mix the RF directly to AF, so it can receive CW, SSB and DSB. For AM it should be tuned exactly right like an SSB receiver receiving AM

OK Thanks. I did not know it was DC. I have built several of those, a 40m meter one as a companion too the 1970s Tuna Tin 2 from QST and a nice little 75 meter one from maybe early 80s from QST. Fit the entire thing including speaker and batteries into a small Radio Shack project box.
Nice little rcvrs

Not a lot of parts yet, but here’s the starting point.

Jon

Ummm... so carrying in that 12ft diameter 3" thick copper tubing for the magnetic loop antenna
will not attract any undue attention??

Chics dig it.

Making this regenerative would add a lot of gain and selectivity. For AM, set regeneration just below oscillation, for SSB/CW, just above.

I just ordered the other parts that I need from DigiKey today. It's just a ha-ha project, maybe just a talking piece, but it won't take too long to put together.

Jon

And about the antenna, I remember my father showing me a trick back in the day. I had an kid's electronics learning board, and one project was a simple broadcast receiver. It had an antenna coil with a ferrite core built onto the board but it didn't work well. He just ran a wire from the wall receptacle's ground to the receiver and it worked great! I'm pretty sure he must've said not to plug it into the small hole one, but those neurons are lost to time.

Jon

You did infect me with this fun project Jon, which is highly appreciated, I had fun. My shack isn't ready yet, so I am limited to just a small experiment.
I did drive a schottky mixer TFM-2 (=SBL-1) with my DDS VFO, and added a transistor LF amp and an input tuning, which is absolutely required in DC receivers to keep the unwanted signals out
Works very nice, I heard many stations at 40.
I had to do it with a passive mixer. The customs in Costa Rica stole all my IC's, so I didn't have any active mixers left. But the TFM-2 gives an excelent IM

That's great!  There's lots of ways to do everything, and I'm glad I sparked something.

To be honest, I scrapped my project.  I experimented with the tank circuit being plugged into the wall socket ground and I tried to make a working antenna.  It worked, but not really well at all. Tuning the tank circuit had little effect on what little I received. 

I was going to go further by using the ground prong as the ground plane for a loop antenna hidden in my duffel bag, but I didn't get too far with that.  This 24-FETter captured my attention and I haven't looked back.

But yeah, customs can be SOB's especially when they're thieves! 

Jon