Need help with a puzzle - partial schematic for HAM Direct Conversion Rx
[Actually, after looking at the BPF (L1 and C2), I can tell this was actually a Direct Conversion Receiver project. From either "73 magazine", "QST", or the ARRL Handbook from 1990, or shortly before. Does that jog any memories?]
Hi, folks!
A while back (OMG it was 1990 or before!) I put together a nice little single band HAM Direct Conversion Rx. (It was for 40M, if I remember correctly.)
It worked pretty well. It was made up of discrete NPN BJT transistors. (All were RCA 40235 UHF Mixer/Oscillator transistors. With four legs. One for a "case ground". NGC161 is the equivalent.)
It was based upon some plans I found. In QST...or was it that years Handbook? Yeah, that is the puzzle...if I knew the answer as to where these plans originally came from...I could resurrect and finish the project.
Because, you see after I had it working FINE...although using a "flimsy" construction technique...I decided to "improve" things by transferring all the components over the a "wire wrap" version. Well, that was a mistake. I never got the "wire wrap" version to work.
So, I put the project back on the shelf, and went on to other things.
Well, I pulled it off the shelf recently, and would like to get it working, again.
So, here is where I need your help. I captured the "as built" version of this in a schematic. And I am hoping SOME one of you might find this schematic familiar enough, and might know where the project originally came from.
I attach a two PDF files. Which show the Audio AMP on page 1, and the Mixer/LO on page 2. This is only a "partial" schematic.
I should also note that the double balanced diode ring mixer is made out of DISCRETE DIODES. And the transformers are hand wound on circular cores.
Maybe that will serve to jog someones memory...
I hope one of you will recognize this project. And can tell me where the complete schematic is.
I would like to get this thing back and working as a receiver.
Jim
P.S. This is a puzzle, and I can't reconstruct the whole schematic myself...because it looks like I have "scavenged" some components off this board. So, for example, the LO is completely missing. So, I don't even known if it ALSO was implemented in discretes...or perhaps was implemented in an IC. I look at the pinouts on that 14 pin DIP socket - and having power on pin 4...sounds a lot like a quad op-amp part. But, then the rest of the pinouts make no sense. So, it was probably implemented in discretes. (I mounted all components on 14 pin DIP wire-wrap sockets. So, the presence of an empty 14 pin DIP socket DOESN'T necessarily mean that there was an IC there in the original circuit.)
P.P.S. Of course, because of file size limitations on this site, and the tools I happen to have...I couldn't fit a decent resolution picture of page 1 from the schematic. So, it is a little hard to read. But, basically I know this must be a Direct conversion receiver because there is 300Hz BPF right after the Mixer! Which means the incoming RF must be mixed down to audio. So, it is a DC Rx.
[Actually, after looking at the BPF (L1 and C2), I can tell this was actually a Direct Conversion Receiver project. From either "73 magazine", "QST", or the ARRL Handbook from 1990, or shortly before. Does that jog any memories?]
Hi, folks!
A while back (OMG it was 1990 or before!) I put together a nice little single band HAM Direct Conversion Rx. (It was for 40M, if I remember correctly.)
It worked pretty well. It was made up of discrete NPN BJT transistors. (All were RCA 40235 UHF Mixer/Oscillator transistors. With four legs. One for a "case ground". NGC161 is the equivalent.)
It was based upon some plans I found. In QST...or was it that years Handbook? Yeah, that is the puzzle...if I knew the answer as to where these plans originally came from...I could resurrect and finish the project.
Because, you see after I had it working FINE...although using a "flimsy" construction technique...I decided to "improve" things by transferring all the components over the a "wire wrap" version. Well, that was a mistake. I never got the "wire wrap" version to work.
So, I put the project back on the shelf, and went on to other things.
Well, I pulled it off the shelf recently, and would like to get it working, again.
So, here is where I need your help. I captured the "as built" version of this in a schematic. And I am hoping SOME one of you might find this schematic familiar enough, and might know where the project originally came from.
I attach a two PDF files. Which show the Audio AMP on page 1, and the Mixer/LO on page 2. This is only a "partial" schematic.
I should also note that the double balanced diode ring mixer is made out of DISCRETE DIODES. And the transformers are hand wound on circular cores.
Maybe that will serve to jog someones memory...
I hope one of you will recognize this project. And can tell me where the complete schematic is.
I would like to get this thing back and working as a receiver.
Jim
P.S. This is a puzzle, and I can't reconstruct the whole schematic myself...because it looks like I have "scavenged" some components off this board. So, for example, the LO is completely missing. So, I don't even known if it ALSO was implemented in discretes...or perhaps was implemented in an IC. I look at the pinouts on that 14 pin DIP socket - and having power on pin 4...sounds a lot like a quad op-amp part. But, then the rest of the pinouts make no sense. So, it was probably implemented in discretes. (I mounted all components on 14 pin DIP wire-wrap sockets. So, the presence of an empty 14 pin DIP socket DOESN'T necessarily mean that there was an IC there in the original circuit.)
P.P.S. Of course, because of file size limitations on this site, and the tools I happen to have...I couldn't fit a decent resolution picture of page 1 from the schematic. So, it is a little hard to read. But, basically I know this must be a Direct conversion receiver because there is 300Hz BPF right after the Mixer! Which means the incoming RF must be mixed down to audio. So, it is a DC Rx.
Last edited:
