Wednesday, 3 February 2010

Wobbulator

Well, after all the fun and games with the IFTs you may remember I finally built a Wobbulator.

The "glitch" in the first response captured with the device was traced to a flyback issue (the point where the voltage controlled oscillator flies back from the top of its sweep to start over at low frequency again).

Here's a decent response of one of my experimental IFTs in close-to-critically coupled tuning, made with the Wobbulator...



Having gone to the trouble of brewing up the Wobbulator and finding it useful, I decided that I would put it in a box for longevity and ease of use...



The front controls...





... give me manual frequency selection (via the knob), manual / swept frequency (switch at lower left) and low / high impedance output (switch at centre). Speaking of high impedance, it is so high that the shunting capacitance of a 1meter coax connector becomes very significant in measurement - I'm learning all the time in this strange, high impedance world!

Having enjoyed more success with the experimental IFT homebrewed with axial RF coils than with home-wound coils on sewing machine bobbin formers (described here , I made a second "axial IFT"...



... and popped it into the valve superhet project (blogs passim).

The result is pretty convincing - best performance so far (although still with too little overall gain - working better into headphones than speakers). I could use the Wobbulator to measure an IF response in situ (this is important, given the effects of stray capacitances etc mentioned earlier)...



Must dash now - got a bout of business travel to attend to!

To tell you the truth, I made this post from the Thai Airways Royal Orchid Lounge in Hong Kong Airport during the business trip - but that's another story. Come to think of it, Bill Meara has a "travelogue" section on Soldersmoke, so perhaps I'll post some travelogue too!

...-.- de m0xpd

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