EMRFD Message Archive 8720

Message Date From Subject
8720 2013-06-11 10:47:37 bquijalvo Getting an SA602AN to oscillate

I recently added the 'EMRFD' book to my library, and I'm excited about getting into experimenting with basic concepts and to start building my own equipment.
I've started out with section 1.8, A direct conversion receiver using a discrete component product detector.
I'm having difficulties getting the SA602AN to oscillate.
Has anyone else built this circuit or a similar circuit and have experienced the same?

I've uploaded a schematic of the circuit I've built, if anyone cares to take a peek. It's in the Files section, Folder: AD0DA, FileName: DirectConversion-test5.pdf.

I've googled for hints, and ran across a few articles where others have had difficulties getting the circuit to oscillate.

Any input would be appreciated.

Thanks in Advance.

8722 2013-06-11 21:16:04 bquijalvo Re: Getting an SA602AN to oscillate
Correction to the chapter.
It's Chapter 1.5 - IC Based Direct Conversi
8725 2013-06-13 07:15:12 kx5x@att.net Re: Getting an SA602AN to oscillate
Hi Bert!
You have probably figured it out by now but I'll comment, and maybe help you or others out.

First, the circuit (602/612) oscillator needs sufficient loop gain for the oscillation to occur. Theoretically just over 1 will work. The caps in the feedback loop set that gain. Sometimes (just like the book title says) you have to 'experiment' with those caps to get the circuit to oscillate (for you). I have over the past REGULARLY had to use different values (usually larger than Wes - or anyone else used). The first time I have to admit that it was frustrating! Its supposed to work! (;-). This is a learning (or just for fun) exercise. If you don't plan to build it (and MAKE it work), then simulation is enough!
Have fun! Its ok to play...

Art / KX5X

8729 2013-06-13 21:28:10 bquijalvo Re: Getting an SA602AN to oscillate
Thanks Art. Since I didn't have variable capacitors of the same values as in the original design, I had to substitute from the very beginning. I ran the calculations to pad the capacitor values to match the inductor value to resonate at the desired frequency. I'll have to experiment with getting the needed loop gain.

Thanks for your input!