I am having trouble building this
http://www.strangeapparatus.com/Theremin.html . I picked this one because of the modular design that should allow me to test each section independently. the pitch reference oscillator so it is producing the frequency it is supposed to. I've also built the pitch variable oscillator and have it producing close to the frequency I want but I don't seem to be getting any change in the frequency when I put my hand next to the antenna. I thought the change might be too small to be noticeable on my scope so I built the mixer circuit to combine the two signals to see what I got out of that. I seem to be getting an amplitude modulated signal on a rather poorly filtered carrier frequency but I don't know if that's what I'm supposed to get or not. Unfortunately my instructions don't give any indication of what waveforms I should see coming out of each of the modules. I also don't seem to be getting much frequency shift out of the mixer either unless I actually grab the antenna.
I can't find any information anywhere on the dimensions or construction of the antenna so I'm just going by the pictures of theremins that I have seen posted on line. I kind of figured that I might have difficulty seeing the frequency shift on the oscillator output which is why I thought that I would connect the two oscillators together via the mixer. I had expected to get a lower frequency wave form out of the mixer with a frequency shift that was visible at the lower sweep rate on the scope. Unfortunately my electronics education is so far in my rear view mirror that I don't know what to expect to see coming out of the mixer. I'm also not sure why the instructions say that the oscillator frequency can be tuned by adjusting the transistor base bias current. I thought the frequency was determined by the RL tank circuit on the collector. Adjusting the trim pot doesn't seem to do anything although maybe that is another effect that's too small for me to observe. I was unable to find the specified BC547 transistor but everything I could find on line said it was just a standard small signal transistor that could be substituted with an equivalent NPN transistor such as the 2N3904 which is what I used. Since the oscillator appears to work I don't think that is causing any difficulties.
http://www.strangeapparatus.com/Theremin.html . I picked this one because of the modular design that should allow me to test each section independently. the pitch reference oscillator so it is producing the frequency it is supposed to. I've also built the pitch variable oscillator and have it producing close to the frequency I want but I don't seem to be getting any change in the frequency when I put my hand next to the antenna. I thought the change might be too small to be noticeable on my scope so I built the mixer circuit to combine the two signals to see what I got out of that. I seem to be getting an amplitude modulated signal on a rather poorly filtered carrier frequency but I don't know if that's what I'm supposed to get or not. Unfortunately my instructions don't give any indication of what waveforms I should see coming out of each of the modules. I also don't seem to be getting much frequency shift out of the mixer either unless I actually grab the antenna.
I can't find any information anywhere on the dimensions or construction of the antenna so I'm just going by the pictures of theremins that I have seen posted on line. I kind of figured that I might have difficulty seeing the frequency shift on the oscillator output which is why I thought that I would connect the two oscillators together via the mixer. I had expected to get a lower frequency wave form out of the mixer with a frequency shift that was visible at the lower sweep rate on the scope. Unfortunately my electronics education is so far in my rear view mirror that I don't know what to expect to see coming out of the mixer. I'm also not sure why the instructions say that the oscillator frequency can be tuned by adjusting the transistor base bias current. I thought the frequency was determined by the RL tank circuit on the collector. Adjusting the trim pot doesn't seem to do anything although maybe that is another effect that's too small for me to observe. I was unable to find the specified BC547 transistor but everything I could find on line said it was just a standard small signal transistor that could be substituted with an equivalent NPN transistor such as the 2N3904 which is what I used. Since the oscillator appears to work I don't think that is causing any difficulties.
