This project grew from the "Lash up direct conversion receiver" thread which was started some time ago. I thought it would be better if I did a seperate thread on it in the relavent section.
Enclosed is the first part of the schematic as developed to date, the second part which I will post later will just be a simple AF Output stage.
I will probably add and on board VFO in the Mixer stage and possibly a sharp AF notch filter in the audio stage centered for CW reception somewhere between 400 Hz to 1 Khz and a switchable 2.8Khz roll off filter for SSB. The PSU and speaker plus the speaker matching transformer will be external. All components shown on the schematic are from my junk box and were all I had to hand so they are not to be taken as the ideal values but they are in the ball park as the receiver works very well.
Lawrence.
Part 2 showing AF stage.
Lawrence.
Hi Lawrence
Just a quick input on cct diag drwg. Others may have their way but this is good for me.
No need for junction 'dots' on lines. They get lost or sometimes forgotten to put on in the first place.
I used to draw resistors as squiggle lines but rectangle are better. In Corel Draw they are given a white fill. When placed over a line (wire) they maybe not be on top, and the line goes thru them, but just 'order' them on top. The advantage is you can just slide the boxes along the wire with no altering of resistor end lines.
My caps are two lines on the edge of a rectangle (box) drawn with 'hairline'. Then fill the box with white and change 'hairline to 'none'. Now want to move the cap just lasso it, complete with rectangle and slide it along (I can set it up so that its centre stays on the line!)
I said creating a component library but I don't really bother. In Corel, draw one item and a duplicate is lasso and hit+ on the numeric keypad. Of course you can step and repeat as many as wanted at any defined spacing.
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Quick cut of a recent one done this way.
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Oh! and sometimes colour helps for complicated diags.
Oh! and I forgot 2.5mh would be 250mH (again for loss of dot)
Gotta dash Yoga calls.
Gary
Thanks Gary, I like the elipse inductors, neat trick, early days yet for me with PC schematic drawing, have always used scribble on paper.
Lawrence.
Screwed up here: don't normally do many inductors. And I was going to miss the bus!
"Oh! and I forgot 2.5mh would be 250mH (again for loss of dot)" WRONG
Guess, continuing the Philips method 2.5mh would be 2m5H and 2.5H could be 2H5
I do have a component library for valves, its cut and paste from a diag I drew earlier!!
And on the Diag the 2K2 should be alongside one of the resistors but you get the principle
Gary
Some general thoughts.....Another alternative to the HRO tuning mech would be one from a scrap BC221 Frequency Meter, the reduction drive is 100:1 (50 turns for 180 deg. rotation) and is a nice unit, the BC221 has a high quality tuning capacitor as well, the value of which is not that far off what's needed, in fact the BC221 has a good cabinet and chassis to build everything in...
Lawrence.