I need a coil antenna for a small car module which takes its input from my cellphone and transmits it at 100MHz. I have thus far learned that I need 8 windings of 0.25 inch inner diameter. I presume I just feed the antenna output into this coil, and the other end of the coil to GND. Is this correct?
Cluebat bludgeoning is welcome, it is very annoying to spend time on making antennas that do not work.
It would not hurt to have a range of ~50 meters on this device, so it can be used in the garden as well.
Posted in EE because amateurradio is pretty silent these days, and most hams are here as well.
Edit: Coil build info came from this page. The FM device I am using is a small plugin module to my phone (microUSB), it states 50mW effect. It has a tiny coil, but its range is 50cm. Haven't measured current draw, but voltage is about 3.7-4.1, depending on charge level. Car antenna is on the roof, so there's no audiolove.
Best Answer
Take a look at this picture that I have amended: -
Well, it's the antenna.
No, that coil is not the antenna - the blue wire is the antenna and I reckon it should be about 75 cm long optimally for the 100 MHz band. This is what the coil does (see L1): -
L1 is part of a colpitts oscillator that is frequency modulated by amplifier Q1.
However, this design is totally illegal (as presented in the guide you linked to) so I can't encourage you to build it at all.