315 mhz tx rx antenna?

What is a good size antenna for a 315 mhz tx rx combo?

Hi,
It should be at least a quarter of the lambda.

Monopole?
If so, it should be 1/4 of a wavelength.

Dipole?
If so, it should be 1/2 of a wavelength.

just as hero999 said, when it is a monopole one like whip antenna, the best antenna length should be 1/4 wavelength, but if you don't have much space to fit in a whip antenna, you can use short whip antenna and helical antenna, i have posted a picture of that.
**broken link removed**
you can visit RF module external antenna design guide at solidremote to see detailed information on antenna design.