Hacker Newsnew | past | comments | ask | show | jobs | submitlogin

> FM antenna has to be quite big no?

No. Here's some food for thought: The wavelengths used for cellular communications in the order of about 0.3m to 0.4m for a lambda/2 dipole that would be an antenna length of 0.15m to 0.2m, which is quite larger than your typical phone.

There's no rubber hose dangling out of modern phones (it used to, 20 years ago), so what's the deal here? Impedance matching,coupling efficiency and planar antenna array designs are. Technically any power of 2 fraction of a given wavelength can be used for an antenna for that wavelength, if assuming an simple wire antenna. But the higher the order, the higher the impedance and the lower the coupling efficiency. With a clever choice of dielectrics the coupling efficiency can be brought back again into manageable regions. And thanks to numerical field simulations we can now design small antenna shapes that can work on much larger wavelengths.

FM radio is receive only, so you do not even require very good coupling efficiency, because you don't have to deal with TX reflection backlash. Hence the problem boils down to designing a reasonably small patch antenna for the 3m band and a receiver circuit that can deal with the high impedance and low coupling efficiency. Back in the day of radios made from discrete components that would have been prohibitively expensive, but these days you can throw a couple hundred of components at some unused corner of your RF grade semiconductor die and have dealt with it.



Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: