Sunday, 6 December 2009

IF Transformers

OK - change of plan (this is a hobby, after all). I was going to build a "Wobbulator" - but it occurred to me that I wouldn't have anything to wobbulate. So - I decided to go right ahead with building the IF Transformers.

I intended to use the sewing machine bobbins sourced by my wife in a layout following that proposed by Harry sm0vpo and others (on Harrys website, look under "Data Technique" for the page "DIY IF Cans" - I won't give a direct link 'cos Harry's going to be moving stuff around, judging by his current problems with Telia).

The first task was knocking up some end pieces - I decided to etch some PCBs as it would be easier in the long run - here's the board layout...

and here is the first batch of PCBs (made using my standard "toner transfer" process)...

The coils, wound on the sewing machine bobbins, were going to sit on 1/4 inch fibre-glass rod - here's a dry assembly...

Glass-fibre rod (and PCB material) is a pig to "machine" - I've got itchy hands from the little splinters!

The coils were wound onto the bobbins - Harry's words and music suggest that you should "wind 335 turns of 32 SWG wire for both the primary and secondary" - I knew (from yesterday's fun and games) that the bobbins hold about 300 turns of #30 wire - so that will have to do.

The resulting assembly starts to take shape...

I fitted a 100pF capacitor to each coil and measured the response with an RF generator and 'scope - the devices peak at about 550 kHz so, once I add the trimmers, everything should be fine. Here are the finished IFTs (sans trimmers - which I'll have to mail-order)...


I got an old tin out of the dustbin - no, credit where credit's due, my WIFE got a tin for me - and I roughed out a screening can - easier than I expected (although it is still a work-in-progress)...


Now we're all set to build the IF stage and the rest of the receiver... guess what I'll be doing next weekend!

...-.- de m0xpd

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