Re: Valve AM transmitter (very very low power!)
I'm not really an expert on coil winding, but i don't think it's to crucial at this sort of frequency. The overall length of my coil is around 85m. It's meant to be one coil centre tapped (it's not in the centre though! closer to 1/3rd ) so keeping the winding next to each other would be preferable. You may need to increase the number of turns on the larger coil since they are slightly further apart due to the insulation. You can find a formula / calculator for air wound coils on the googletron! (someone - back up the thread calculated the micro-henries for the coils - so you may want to aim at those).
To be honest i just guestimated it, based on previous experience of building crystal set's. The best way to be sure is to measure the frequency using a scope or DVM (i got one from China, cost #9.50 and does frequency up to 20mhz along with V/A, AC/DC and ohms)
Just experiment, that's the fun! You could for example put the smaller winding on top of the bigger winding, as long as you keep the direction the same (ie the correct phase for the feedback to make it oscillate)
Sorry i can't be more helpful.
coop
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