Most of my parts have arrived and I am beginning the process of planning my first official scratch build. For sure this is not a true scratch built radio like the OMs who had to learn 20 WPM CW in the 50s. BUT my goal here is to complete a project from a schematic and learn a little about what challenges I will face in the planning phase of circuits. I’m confident there will be LOTS of little lessons along the way.
Direct Conversion Receiver from EMFRD (out of print currently)
When I failed building my Regen last year I learned that you should
think about the layout prior to actually building the circuit. Most schematics do not represent reality in any way. Take a look at the schematic to the right. Do you see the problem in this picture? Look closely. Do you see it yet?
How many 8 pin DIP chips have you seen with pins on all 4 sides of the chip? The beauty of the 8 pin DIP package is that you can count on the numbering of the pins and that there will be 4 pins on each side. With that in mind how am I going to lay out this circuit?
My attempt at drawing a real life representation of the layout.
I got out my lab notebook and started sketching out how the circuit would lay out. I really wasn’t thinking about the realities of pin layout when I started. I was aiming to make the chips line up vertically side by side just like the drawing. I was hoping that I could make it as pretty as something from AA7EE. I am by nature not a very organized person, but I appreciate people who do and its something to aspire to right?
Well as you can see from my first attempt, this is not an ideal layout. If I were to have just started without drawing it out first, I would have had jumper wires all over the place. Most concerning to me is that the LO (bottom of the schematic) would have a low-level RF signal traveling on long jumper wires to pins 6 and 7 on the NE602. Mission accomplished, I learned!
My second attempt turned out much better
In my second attempt you will see that I am not an artist, but this layout at least makes sense. I’ll have one long trace to get power to both chips, but the individual circuits should be able to sit nicely and not interfere with one another. Also any connections with RF will be short and direct. I am confident that this circuit can be built. I need to do a little more research as I do not have a 5V or 6V power supply so I want to figure out if I can add a 5V regulator and use a 9V power supply. I know it can be done, I’ve just never done it so I want to make sure I connect it correctly and don’t let out the magic smoke.
More to come. . .
I’m a relatively new ham. Got my license, joined a club and I’m having fun! I enjoy CW, pedestrian mobile, backpacking, and I dream of building radios at some point. At present I have a wife and daughters so my building time is limited.
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