help with inductor value

[smoguzbenjamin]

Hi

I got a PCB layout from marcos - munky, for a wireless FM transmitter. It's got the inductor imprinted on the board by means of some parralel lines.

url: http://scorpius.spaceports.com/~ubermaus/bugfm/bug.html

Could I recreate this on a 1:1 scale to make this inductor (when prototyping) or can someone tell me what inductor to buy, so I can make sure this thing works before I get into making PCB's...  :?

[Ansil]

remember another circuit similar to this  where the inductor was such a value that the coper tracings on the board that was drawn similar to this, was actually the inductor.  don't remmbber where i saw it though and that seems  to be what is implied unless i read it wrong.

[smoguzbenjamin]

yes, the parralel lines ARE the inductor. But I don't wanna build a PCB to find out it don't work. So, is there a way of figuring out what value the inductor is?

[brett]

This is a bit of a guess, but wouldn't you get the same inductance if you used the same number of turns and the same diameter of turns as on the PCB?  If you HAVE to know the value, there are many formulae around for calculating it.  (using one of those formulae I have estimated that the inductor that I used was close to 1uH, maybe a bit more)

The FM transmitter I made up came in a kit from the electronics store (about $12 incuding a battery, mic, everything!).  The inductor was about 6 turns with an average diameter of about 0.3".  Pity it wasn't good enough quality for a wireless guitar.  But the kids had fun trying to listen in to conversations in "bugged" rooms!  I'd suggest avoiding the simple, 2-transistor circuits, and go for one of the FM transmitter chips.  For a few $ more they'll offer much higher quality.