Direct Conversion Receiver with DDS VFO

So not to be outdone with just one project on the go, I also get it in my head to rebuild the 2-IC DC Receiver from page 1.8 of EMRFD. I have built this simple receiver before, it was one of my first projects ever and it worked first time out of the box, well kind of.

My original was built Manhattan style, but at the time, being rather newbie, i was not able to make the LC oscillator circuit with sufficient Q to make the thing work. It was yanked out and initially replaced with an xtal, making it rock bound and of limited use, then the xtal was removed and replaced with an Arduino DDS VFO and my love of DDS was born LOL.

My first project that gave excellent results, I was receiving stations from all across Australia, New Zealand, Japan and the USA. It was thrilling. I was now hooked on homebrew.

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Above is the schematic of the circuit, i have changed out the local oscillator for a DDS VFO, and i have made a couple of minor changed to the audio amp, mainly double the gain it will now put out maximum gain, the only issue no gain control on the audio amp.

 

dc-rx

Board was laid out in Sprint Layout, with extra holes drilled for mounting the DDS board onto it.

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Its a nice simple project, wont take long to solder it up and get it on the air and tuning the 40m band.

UPDATE:

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So it is all together and it works ok. I did have to change a few things, mainly making the audio single ended rather than differential, this gave much more audio at the speaker. Also the tank, while it functions, does not seem to do all that much, tuning it by the trimmer, yields no change what so ever. Its something i will need to look at.

While its working, it could do with some improvements, especially to the front end. Here is a video showing it working.

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3 thoughts on “Direct Conversion Receiver with DDS VFO

  1. hi

    Im doing the same thing – DDS VFO into a DC receiver. Question, did you have to filter / and or attenuate the DDS output before feeding it into the NE602 ?? I am not having success and wondering if the 2v square wave DDS output is causing issues. Which pin on the NE602 did you connect the DDS to and via a capacitor??

    Cheers

    Marty

    1. No filter, always ac couple with a cap, pin 6 if i recall off the top of my head, the square wave is fine, mixers are non linear anyway and make harmonics, though in this project i was using a sine wave output on the dds and it was about 300mv peak i think. I would have to go back and measure it to be sure.

  2. thanks for the reply, yes coupling with cap, still no success, ha ha – im suspicious of front end so will re take a look at the inductors – cheers

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