dietermoreno
- Dec 30, 2012
- 238
- Joined
- Dec 30, 2012
- Messages
- 238
Variable inductor instead of varible capacitor in FM crystal set.
So I don't have a varicap, so I wondered if I could modify my circuit to use a variable inductor instead and use a fixed capacitor. Variable inductors are extremely easy to build, but variable capacitors are hard to build (especially at a small enough size for VHF).
I thought if I make the coils smaller I can use more coils so I can have better selectivity with taps on the coils.
The original schematic uses a varible capacitor and has 4 coils wound around a Sharpie marker and then the coils are removed from the Sharpie and they slightly expand.
My new schematic uses a fixed capacitor and has 16 coils tightly wound and tightly spaced around a bic pen, which is about half the diameter of a Sharpie.
Also, if I made the center inductor lead variable as well, the bandwidth could be adjusted for optimal reception, with the most distance apart from coil #8 to coil #1 for the greatest bandwidth, and with the least distance apart from coil #8 to coil #1 for the lowest bandwidth. Decreasing the bandwidth of the slope detection can help to receive farther away stations 15 miles away and increasing the bandwidth of the slope detection will provide the optimal sound quality to receive the local station 5 miles away.
The power supply of the transistor is not currently shown because it is implied and it is not important to understand using a variable inductor instead of a varible capacitor .
File attached. Please tell me if it will work or if I should give up and get a varible capacitor .
Thanks!
So I don't have a varicap, so I wondered if I could modify my circuit to use a variable inductor instead and use a fixed capacitor. Variable inductors are extremely easy to build, but variable capacitors are hard to build (especially at a small enough size for VHF).
I thought if I make the coils smaller I can use more coils so I can have better selectivity with taps on the coils.
The original schematic uses a varible capacitor and has 4 coils wound around a Sharpie marker and then the coils are removed from the Sharpie and they slightly expand.
My new schematic uses a fixed capacitor and has 16 coils tightly wound and tightly spaced around a bic pen, which is about half the diameter of a Sharpie.
Also, if I made the center inductor lead variable as well, the bandwidth could be adjusted for optimal reception, with the most distance apart from coil #8 to coil #1 for the greatest bandwidth, and with the least distance apart from coil #8 to coil #1 for the lowest bandwidth. Decreasing the bandwidth of the slope detection can help to receive farther away stations 15 miles away and increasing the bandwidth of the slope detection will provide the optimal sound quality to receive the local station 5 miles away.
The power supply of the transistor is not currently shown because it is implied and it is not important to understand using a variable inductor instead of a varible capacitor .
File attached. Please tell me if it will work or if I should give up and get a varible capacitor .
Thanks!
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