DIY Variable Capacitor for Homemade AM Radio Receiver

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SUMMARY

The discussion focuses on constructing a homemade variable capacitor for an AM radio receiver project. Participants suggest aiming for a capacitance value around 100 pF to effectively receive two AM radio stations. Recommended designs include a parallel plate capacitor with an adjustable plate and a coaxial capacitor, where a rod is positioned inside a tube. An article on building air variable capacitors is also referenced for further guidance.

PREREQUISITES
  • Basic understanding of capacitor design principles
  • Familiarity with AM radio frequency requirements
  • Knowledge of parallel plate and coaxial capacitor construction
  • Experience with mechanical adjustment mechanisms (e.g., screws)
NEXT STEPS
  • Research the construction of air variable capacitors
  • Explore the principles of capacitance and its role in radio frequency tuning
  • Investigate the specifications for AM radio frequency reception
  • Learn about alternative capacitor designs for radio applications
USEFUL FOR

Students in physics courses, hobbyists building AM radio receivers, and electronics enthusiasts interested in capacitor design and radio frequency applications.

DawsonH
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I have to make a homemade AM radio receiver for a physics course I'm doing, and I'm looking for any suggestions on the best way to make a homemade variable capacitor. I'm not expecting anyone to do my work for me of course, but any suggestions that anyone could offer would be appreciated.
 
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Do you know values required?
 
I need to be able to receive two AM radio stations. I haven't figured out what values I need yet. I'm just looking for different suggestions about how to construct one.

Edit: Maybe something around the 100 pf range.
 
Last edited:
You can make a reasonable parallel plate cap with one adjustable plate that is moved by a screw. But to get more than a couple of tens of pFs, may be tricky (unless you just make a big box).

Easier still may be a (cylindrical or) coaxial cap (a rod inside a tube), with the position of the inside rod adjusted by means of a simple screw.
 
Here is an article on building air variable capacitors.

Mark
 

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