Inductors for Colpitts Design AM Transmitter

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When designing an AM transmitter using a Colpitts circuit, selecting the right inductor is crucial, with options including SMT, toroidal, and ferrite core types. The choice should be based on the operating frequency, with a self-resonant frequency (SRF) significantly above 1.6 MHz recommended for optimal performance. Additionally, understanding DC resistance (DCR) and saturation current (Isat) is important to ensure the inductor can handle the required current without exceeding limits. For a transmitter broadcasting over a distance of about 100 feet, the inductor's specifications should align with the desired frequency range of 0.5 MHz to 1.6 MHz. Proper inductor selection will enhance the transmitter's efficiency and reliability.
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I'm trying to design a AM transmitter using a colpitts design. I see many different types of inductors available for sale, smt, torrid, dip, ferrite core, iron core, etc... Which one should I buy? I know they have different Q values and max current. What do you think the max current would be for my transmitter if it only broadcasts over a 100ft or so?
 
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powzoom said:
I'm trying to design a AM transmitter using a colpitts design. I see many different types of inductors available for sale, smt, torrid, dip, ferrite core, iron core, etc... Which one should I buy? I know they have different Q values and max current. What do you think the max current would be for my transmitter if it only broadcasts over a 100ft or so?

What frequency is your transmitter? Be careful just broadcasting a signal -- The FCC has rules about how much power you can put out in different bands without a license...

You will choose inductors based on the frequency (hence the SRF makes a difference), the DCR, and Isat. Beyond those things, you will usually choose the cheapest and smallest that meets those requirements.
 
I'd like to make it broadcast over commercial AM so that it can be picked up by a home radio. I'm not too concerned about FCC as it won't be broadcasting off my property and it's really only for learning purposes. So about 0.5Mhz to 1.6Mhz. If I understand correctly, I should pick a SRF value much greater than 1.6Mhz? What is DCR?

Thanks for the reply.
 
powzoom said:
I'd like to make it broadcast over commercial AM so that it can be picked up by a home radio. I'm not too concerned about FCC as it won't be broadcasting off my property and it's really only for learning purposes. So about 0.5Mhz to 1.6Mhz. If I understand correctly, I should pick a SRF value much greater than 1.6Mhz? What is DCR?

Thanks for the reply.

DCR is DC resistance. Isat is the saturation current (which you want to stay below). Yes, just choose the SRF well above your operating frequency to be sure it's still an inductor.
 
powzoom said:
If I understand correctly, I should pick a SRF value much greater than 1.6Mhz? ...
10X will do.
 

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