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.

 

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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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Super VXO

Ok, so mostly I am a DDS and Arduino kind of guy, they just work, they don’t drift and they are super simple. But sometimes, you get that “Retro” kind of nostalgia happening and a desire to build something rock bound. I have a ton of crystals in matched pairs for 7mhz, enough to cover the whole CW portion to 7.050. So i thought, what the hell, I will make a Super VXO, and incorporate it into a transceiver if it proves to be stable enough.

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So i went looking for a suitable circuit to modify to suit my parts bin and needs. And i came across this one above. Varactor tuning is nice, as getting quality air variable caps and reduction drives is impossible, so varactors are must. The only thing i changed is the inductor as I do not have any Toko IF coils, and the only other thing i changed was to add an unbalanced to balanced transformer to split the signal in to, one for the receiver and the other for the transmitter. The original article and associated info for this Super VXO can be foundĀ HERE!!

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Laid the board out in Sprint Layout, and after ironing out the bugs with the help of Ben VK6FBLJ who put his eyes over the layout and noticed all the errors, the gerbers were then converted to gcode for routing.

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Could fit 2 boards on the one sheet of FR4 the above picture is the boards on the mill deck still after routing and v-cutting in two.

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And this is the finished board after being cleaned with steel wool and a coat of PCB lacquer being applied. They have come up rather nice looking. More to come on this, after they have been built and tested to see how stable they are.

UPDATE 1:
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Most of the parts are installed, I threw in a pair of 10mhz xtals for testing with, they will not be the what is used in the final board, but are good enough for testing purposes. Just have the inductors to wind, 10 turn pot to wire up and the 8v regulator to install and it is ready for smoke test. Oh and i was able to find a MV2109 varactor in my semi conductor box, so, no cheeping out and using a silicon rectifier.

UPDATE 2:

Well i cannot get this thing to start oscillating. Have tried just about everything i can think of, will post back when i work out what the case is.

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