Practical radio astronomy receivers incorporate frequency conversion because it is technically more convenient to amplify, filter, delay and cross-correlate signals at a fixed intermediate frequency (i.f.) than at their original, changeable (and often higher) radio frequencies. The frequency conversion is done in one or more mixers, in which a non-linear element (usually a diode) forms signals at the sum and difference frequencies between the astronomical signal and a tunable local oscillator (l.o.) signal.
microwave signals are shifted down in frequency by combining them with a locally generated signal in such a way that the difference in the frequencies is generated. The local signal is generated by the local oscillator. In project Argus type systems, the frequency is shifted from around 1420,000,000 Hz, to somewhere around 1,800 to 20,000 Hz (centre). There are many reasons for doing this, but if it weren't one would still need an accurate local references of the same precision, which needs to be significantly better than the bin width in 1420,000,000 Hz.
A circuit to generate a stable RF frequency that is mixed with the received RF signal to obtain an IF output signal. The local oscillator will operate at a frequency above (or below) the desired RF frequency by an amount equal to the IF frequency of the receiver.
An oscillator used to produce a sum or difference frequency which will heterodyne with a desired incoming signal frequency to produce the intermediate frequency of a radio receiver.
an oscillator whose output heterodynes with the incoming radio signal to produce sum and difference tones
A sinusoidal signal source used to translate RF signals to IF. LOs usually have to be very stable and free of harmonics, or the IF will contain spurious signals.
A single-frequency reference signal of high purity which is used by a mixer to convert a communications signal to a higher or lower frequency band.
A reference signal generating circuit that is contained within a receiver or transmitter. The LO signal provides the high frequency bias to a mixer. The local oscillator signal is typically at a higher power than the signal power. An optimum local oscillator power is required to obtain low conversion loss and good RF match to the mixer non-linear impedance component. Normally optimum local oscillator powers are in the range of -3 to +13 dBm for most common diodes or FET's.
A device used to supply a stable single frequency to an up-converter or a downconverter. The local oscillator signal is mixed with the carrier wave to change its frequency.
An RF component which produces a perfect sine wave signal: it is connected to ne of the ports of a mixer.
A local oscillator is a device used to generate a signal which is beat against the signal of interest to mix it to a different frequency. The oscillator produces a signal which is injected into the mixer along with the signal from the antenna in order to effectively change the antenna signal by heterodyning with it to produce the sum and difference(with the utilization of trigonometric angle sum and difference identities) of that signal one of which will be at the intermediate frequency which can be handled by the IF amplifier. These are the beat frequencies.
