Question about antenna impedances

[obrien136]

My question is, when you are buying a transmitting antenna for a RC controller, how do you know what the impedance of the antenna is so that you can match it to the transmitter output? It doesn't seem to be listed anywhere in the product descriptions in the ads on the internet.

George

 

[chuckey]

You are correct. if the aerial is 1/4 wavelength long AND the transmitter has a decent earth (or a 1/4 wavelength counter aerial. Then the aerial impedance can be taken as 75 ohms. Most RC aerial are too short (< 1/4 wavelength), so they look like a low value resistor (20 ohms?) with a capacitor with an impedance of 50 ohms in series (figures pulled out of the air ). Inside the transmitter there will be a little coil to tune out the capacitor. The aerials on the model are even worse!!!
Frank