80m VXO

So today i thought i might be fun to whack together a VXO for 80m and see just where i landed me. Now i know that pulling crystals very far is not an easy thing to actually do, especially when they are on the lower end of the spectrum. So with this in mind, i set my initial goal as 1khz pull. I figure if i can get that, its kind of usable in other projects.

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First job is to get on google and find a simple schematic, with that out of the way, I can get to putting the ugly back into ugly style home brewing and slap something together on some scrap board.

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And slapping together is just what I did, a pair of 3.6864 xtals, with 10uH series inductance and 170pF of capacitance in the polyvaricon.

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Give it some power and connect up the scope and freq counter and am greeted with this ugly waveform, harmonics, bias, its a mix of everything that is wrong in the world. So let see how far we can pull these bad boys.
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High freq is 3.6867

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Low freq is 3.6863 HAHA we managed a whole 400hz agility, as good as useless, but it was rock stable, pun intended. So i did a but of goggle foo and found that I can get much better pulling power with more inductance, 10uH is orders of magnitude not enough, so i added another 200uH in series and got a total pulling power of 2khz. 2khz is not much in the scheme of things, but, for a cw 80m rig, 2khz is a nice slice of spectrum to be frequency agile on.

So, whats next? rip out the xtals and drop in a ceramic resonator and adjust the series inductance to suit. Should see a good pull range with that.

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