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Tuesday, January 24, 2023

Update on High School Direct Conversion Receiver Project + .asc File

So far, in response to my recent request for testing,  no one has stepped up to build the DC receiver Dean KK4DAS and I are testing out.  We did get a couple of comments explaining why guys are opting not to help, but so far no other builders are actually melting solder in response to our recent request. 

So Dean and I decided to each build second versions of the receiver.   That will bring the total finished build population to 4.  I finished my second version yesterday.  Picture above.   It works great.  

One change:  The emitter resistor on the final AF amp was too low in value.   The transistor and the transformer were getting hot.  I switched from 10 ohms to 100 ohms and the problem disappeared.  I have made the change on the LTSpice Schematic.   Here is the .asc file (I hope!) : 


Dean posted the .asc file (and some other info) here: 


If you have trouble accessing that file, please let me know and I will try to e-mail it to you.   In any case the schematic appears here: 


You will notice that this Spice schematic actually works!  The PTO turns on, and I put a simulated RF signal at the antenna port.  Audio appears at the output.  

Time is getting very tight.  Dean and I will begin presenting this project to the high school students on February 2.  So it is not too late to help. But helping is, of course, strictly voluntary -- if you are reluctant to build this thing, DON'T!   


  1. Here is a link to a Google Drive with STL file and LtSpice models as well as my fancy hand-drawn schematic. For the PTO former you'll need a 3" 1/4x20 brass screw and 2 1/4x20 brass nuts. You need to print the PTO former scaled to 110% to fit the standard nuts you can get at your local big-box store.

    Here is the link:

    While we appreciate the suggestions about alternative circuits it would be very helpful for a couple of experienced builders to build to the schematic with no changes. We're trying to QA the project before setting the high school students loose on the build. Bill and I have both built the receiver a couple of times now with good success, but it is always helpful to have another confirmation. As Bill has said, we made various compromises in the design to keep the circuit simple, but not too simple, to produce a nice sounding 40-meter receiver.

    73 and happy building,

  2. I'll give it a shot, but I don't think there's enough time to source the components and build everything before the 2nd. Presumably the students won't be building the entire thing on the first day, though, so maybe I can still be of some help.

    -Sam, AI7PR

  3. Thanks Sam! Dean may have more info soon on a parts list. 73 Bill

  4. I did not see your request for help....


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