Zero radio frequency refers to the phase of the frequency or the wave of the frequency. For example, two waves can be 90 degrees out of phase, or they can be 180 degrees out of phase, in which the crest of one wave is in the trough of the second wave. In a 180 degree phase, the effective received signal strength is zero. Whereas, in the scenario where the signals have zero degree phase separation, the received signal is much stronger, potentially as much as twice the amplitude.
Zero radio frequency has been proposed in radio reception design to increase the received signal strength, as the zero radio frequency refers to the effect of zero degree phase separation, which increases the overall signal strength for a receiver. In a super heterodyne receiver, the most common type of radio receiver, a zero-IF, with IF standing for intermediate frequency, refers to a system in which the local oscillator in a mixing arrangement runs at the input signal of an IF, resulting in zero Hz, or zero frequency. This differs from a typical AM radio, where the IF is 455 kHz or a typical FM radio where the IF is 10.78 MHz.
The zero-IF design is also sometimes called a direct conversion or homodyne architecture, and uses a local oscillator set equal to the desired carrier frequency, or as close to zero as possible. This offers a benefit of eliminating some of the related circuitry needed for receiver and avoids the problem of image frequencies, which are generally managed and filtered. However, this receiver type is not often used as it places extreme demands on the oscillator performance and mixer performance, and any DC offsets or imperfections in the mixer can quickly corrupt the zero-IF output and result in poor system performance. It can also have issues of achieving sufficient dynamic range, which is important for most received wireless signals.
The technology has been used in the Building Block 38 (BB38) of the US Navy CVA VAST test system, which was a technology and method copied from the Hewlett-Packard HP3590A analyzer, which has since been discontinued.
A more popular alternative to zero-IF technology, which works to avoid the drawbacks of a zero-IF receiver, is software-defined radio, which is capable of tuning, demodulating, and decoding a received signal. And this system uses high-resolution analog to digital conversion of the original received signal band rather than just a desired signal.
