# If antennae work best at full, half or quarter wavelengths, why don't received signals at 1, 1/2 and 1/4 wavelengths interfere with each other?

How does a simple radio receiver-antenna differentiate between incoming wavelengths that are the same wavelength as the antenna, one-half and one-quarter?

Or would I just hear static unless I have a good changing-capacitance LC 'tank' tuner thingie?

(I am obviously still a beginner here... )

• Radio waves at different frequencies don't interfere until you put them into a nonlinear device like a receiver. That is why you use a tuner/filter after the antenna to extract the signal you want from the range of signals on the antenna. – user1850479 Jul 4 at 15:10

This answer shows how the impedance presented by the wrong sort of wavelength signal will be high (therefore ineffective) in many cases but, for a quarter wave monopole it can still adequately receive transmissions at 0.75$$\\lambda\$$ etc..

Of course, we use band-limiting filters to prevent pick-up from beyond where we are actually interested and that band-limiting is profoundly and intentionally sharp at letting in only the signal we want to receive. For conventional receivers we use a multi-stage IF amplifier (see green in picture below) and they are designed to be just wide enough to let in one dedicated channel in the part of the spectrum we are interested in: -

IF stands for "intermediate frequency" and the IF "strip" (as it used to be called) usually comprises several filter/amplifier stages all of which are band-pass in nature.

How does a simple radio receiver-antenna differentiate between incoming wavelengths that are the same wavelength as the antenna, one-half and one-quarter?

It doesn't - the IF strip does that for conventional radios.

In a simple radio receiver, the required signal is isolated by making the antenna resonant at its frequency, using either a parallel or a series resonant circuit.

The parallel resonant circuit presents a very high impedance to the required signal which results in an increase in its voltage driving the detector. All other signals are bypassed to earth.

On the other hand, the series resonant circuit presents a very low impedance to the required signal which results in an increased current through the detector. All other signals are blocked.

Should a strong interfering signal get through, it is either blocked or bypassed by use of an additional parallel or series tuned wave trap.