Wednesday, June 1, 2011

AutoDyne Receiver Project

I have been working with "virtual" electronics for the last few days. I must have inadvertently turned a corner without me noticing. I have not been in my Shop for days, most of my work has been at the computer in the Loft.

In the past, I have always breadboarded my circuits before creating Homebrew PCB's, which I think is still a good idea. But, professionally manufactured PCB are so cheep, that I decided to skip the breadboard stage, with the idea that I can re-do-it if the circuit fails miserably.

Normally I would not Blog about a Project until it is successful, but for this project "you are going for a ride", and you will see the success or maybe a total failure.

My current little project is to build an "AutoDyne Receiver", as documented by Nick - WA5BDU and describe at Wikipedia.

This circuit is a Frequency tracking receiver that outputs the station audio for a speaker circuit, and the RF carrier frequency. If it is configured to receive WWV (say at 10MHz) the RF output can be used for a frequency standard (or at least that what it says in the documentation).

This circuit was originally constructed with discrete transistors, and then with a CA3046 Transistor Array. But, the CA3046 part is currently almost unobtainable (it must be made of unobtainium :-), I will substituted with five SMT 2N3904's.

This is what I have so far, note the circuit has been redrawn in sections, and parts from my junk box have been substituted where necessary. Refer to the original link above. I hope I have not miss re-creating the circuit.

The AutoDyne Receiver Circuit in DipTrace

Proposed Circuit PCB - 1.6x.9 Inch

A DipTrace 3D View

As with all of my HomeBrew PCB Circuits I have tried to make this board as small as possible, is will be 1.6 x .9 inches and will be powered initially by a 9 Volt Battery (if you know my projects, what else would you have expected?).

The PCB is now on order. If all goes well, my small board with be merged via DorkbotPDX onto a large manufacturing board on Jun 6th, and then enter their normal manufacturing process. My board(s) should be returned around Jun 15th.

This little project has been on my drawing board for more than a year, only recently have I pushed it along to the PCB stage, my original planned implementation used much larger parts. Now, I will use small 0805 and 0603 SMT parts. After looking at the photos above, I could have (with more work) held out for an even small build/design. A lot of space is taken up by the Audio connector (lower right on PCB)?

Later, I will report the results (or failure) of my attempt to skip the Breadboard stage for this project.

Again, Thanks to Nick - WA5BDU for documenting (and his mods) of the original circuit. Note: many others have had their hand in the circuits creation. The link is an interesting read.



  1. I found this autodyne circuit a couple of weeks ago. I've been looking for a reasonably-accurate frequency reference to calibrate my frequency counter. I had a PCB made, and put it together. My circuit uses a CA3146E which I found on eBay. I am using the original design by K7QO & VE3DNL, which can be found on the Brainwagon site.
    I used a different L1 at first, and the oscillator would not run. Reducing the value of R1/10K fixed that, but I ended up adding a regulated 12V supply instead.
    I can hear some beats at certain settings, but no modulation at all. This is with a 1/2 wavelength dipole through a commercial 300-75 ohm balun. Amplified LO output is 150mV-PP, not enough to trigger my 1989 ARRL Handbook frequency counter. So thus far it has been a total waste of time. If anyone else has suggestions for improvements, I'd love to hear 'em.

  2. Greg Morris here again (as unknown, above).
    I continued tweaking the circuit, using an air-variable cap for C6, and using one of the Radio Shack 9V pocket amplifiers (based on the LM386) at the output of the on-board LM386 to really boost the audio. One possible improvement would be to use the leftover transistor in the CA3146E (or equiv.) as a preamp, so the unit doesn’t require an external amplifier.
    I am getting much better results. The LO output *does* track the received station, as described by Nick (see link in article). I can usually hear WWV or WWVH, sometimes both at the same time. I was able to use the LO output to also tweak my home-built ARRL frequency counter (needed more localized supply filtering) and so now I have achieved the goals I set out to accomplish with this unit. I more than doubled the sensitivity of the frequency counter 10 MHz front-end, improved the stability of the 550 MHz front-end, and got it calibrated within a Hertz or two.

  3. Thanks Greg, for the interesting updates of your project and the use with the counter. I may revisit this circuit to do something similar.

  4. Thanks Greg, for the interesting updates of your project and the use with the counter. I may revisit this circuit to do something similar.