Re: Building the 'Minimod' AM modulator-questions!
I built one and had it published in the BVWS Bulletin Autumn 2000, but it uses a MW channel crystal with an output power that easily covers an average home and garden. It uses two BD131s and a BD132.
I've also designed one using a IRF510 as the output device which is series modulated with a TDA2003 audio amp and a small mains (mod) transformer, but that also uses a MW channel crystal. It covers the house and garden with just a telescopic whip.
But to be honest, these days with fewer stations on MW any old crystal can be used in the many gaps between stations. I think 1MHz crystals are quite cheap, but it's a nasty 1 kHz away from a channel!
I really wouldn't advise using a MiniMod type VFO without extensive buffering and screening for a more powerful circuit - more trouble than it's worth.
As long as you keep the antenna very short and signal strength down, a couple of hundred mW PA will have the required coverage just for your property. Remember that the antennas will have a very, very low efficiency so you're unlikely to attract attention.
Have a dig around the internet. There are a few designs that will do what you want, but are best not mentioned here...
Ian
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