Monday, May 16, 2016

Direct Conversion Reciever

I've been in a holding pattern on some other radio projects, so I decided to start another one - the "IC BASED DIRECT CONVERSION RECEIVER" from section 1.5 of EMRFD.  (Chapter 1 that has this project is online here.)  This is your basic ne602/lm386 combination you find lots of places.  I built mine for 40m.

The variable capacitors are little polyvaricons.  I got these cute little dials for them, but still need to find some screws to hold them in.

I threw some wire out the door and was able to hear some stations!  The thrill of hearing anything on a radio you built yourself is *awesome*.

Unfortunately, it is quickly replaced by the annoyance that it isn't doing *quite* what you want.  For one, it isn't quite on the frequency I want.  I made a rookie mistake and mounted the variable capacitors on veroboard (it was late and I was excited to be close to done...), which seems to have added a bit of capacitance.  I also found I had a wrong cap in somewhere.  So, I haven't quite got it to the 7-7.125 MHz range I was going for.

Also, it is *really* hard to tune.  I think a third padded down cap would help a lot, but getting it right on a station took a lot of practice.  Even as I got the hang of it, it was kind of harsh to listen to, and the whining as you got close to a station got old quick.

All in all, I'm counting this as a huge success.  But I don't think I'm going to keep it as is for long.  I got an AD9850 off of Ebay the other day that I think I'm going to try in place of the tuned circuit here.  Partially because I want to play around with the DDS, partially because the little variable caps here are fiddly.

This is my first Manhattan-style build, and I looked at a *lot* of examples before starting.  I need to give huge props to KK6GXG - his build was a huge inspiration.


  1. Greetings Ben,

    Thank you for the kind words. I am very pleased that my post was helpful to your build of this DC receiver. One of the greatest joys in amateure radio for me is knowing that I contributed in some way to someone else's project success.

    Keep making solder smoke!

    ~Jon KK6GXG

    1. It really did. This was first time using Manhattan/MePads/etc, and I spent ages trying to get my head around how to lay out things. The close-up pictures you had of the way you did your ICs was what finally got my head in the right space.