Types of inductors

[Powzoom]

I've been reading up on radio transmitters and have decided to build one. I'm going for a small simple AM transmitter with maybe a range of a 100ft or so. I'll probably go with a Colpitts design but my question is what kind of inductor do I need? Does it matter? I see dip, color wheel, ferrite, torrid, and special RF inductors. What is the difference? I know some are rated at higher currents and Q values but what would be a reasonable max current to expect going through the inductor in my transmitter? I'd rather not build one myself. Would these be usable **broken link removed** ?

Thanks.

 

[Ned G7WJK]

Hi Powzoom,

Unfortunately you do not state which frequency you wish to transmit on. The answer to your question depends on the frequency.

The inductors shown on the link are not suitable as they have low Q (due to their high internal resistance) and the inductor in an oscillator needs to have as high Q as possible.

The construction of a suitable inductor is relatively simple, for instance, if you were to be operating at VHF/UHF the inductor could just be half a dozen turns of stiff wire.
Or if you were operating at lower frequencies, then several tens of turns of insulated wire aroung a ferrite ring would do the job. The precise number of turns depends on the frequency and the size and composition of the core. For more info about that, see the American Radio Relay League handbook, also the websites of manufacturers amidoncorp.com and fair-rite.com. It has to be said though, that neither of these websites is very helpful for beginners.
You mention the current rating. Don't bother about it, as you only wish to transmit a short distance anyway then the power involved is minimal.
One final point. Is what you wish to do legal where you are ? You may find that it is not.

Ned

 

[stevez]

I googled on "am broadcast transmitter schematic" and found a website that discussed antique radio transmitters. I am wondering if the inductor used - or a similar one available from the same source (Antique Electronic Supply) might not be sufficient.

As Ned pointed out - be sure what you do is legal. Give your location and we might be able to help with that. In US the rules are relatively simple - would take a minute to look up but it sounds like you can do what you want to do - legally.

 

[GonzoEngineer]

Back in high school (1965) we had a hobby club and we all built a ""Knightkit, 5 tube, superheterodyne AM receiver. We also built a 2 tube AM Transmitter kit and had our own radio station in school.

It was legal back then, the only limit was your transmit power and a couple of rules.

If it was legal back then, then I am sure it is legal now!

A Ham Radio Operator would probably know where to find out the exact FCC Rules