Intermediate frequency (IF ) (English Intermediate frequency / IF ) is a term used in electronics. It refers to the fixed set in superheterodyne receivers used frequency to which downmixed coming from the antenna reception signal is amplified and demodulated. The advantage of a permanently set resonant circuits is that the superheterodyne receiver in the entire area gets constant reception characteristics.
Only the reception signal which is offset by the value of the intermediate frequency from the oscillator frequency of the local oscillator (LO) to the intermediate frequency amplifier to pass:
The intermediate frequency is usually lower than the input frequency, since the circuit scale is lower at low frequencies than at high amplifiers. The exact value depends on the receiver equipment from: With AM radio receivers in the long, medium and short wave range of 460 kHz is worked in FM radio receivers, the frequency has established 10.7 MHz, in television receivers 38.9 MHz for the image signal. The intermediate frequency of the tone is obtained from the mixture of the frequency-modulated audio signal coming from the transmitter with the amplitude-modulated video signal. The distance of these two signals is e.g. set when analog TV system PAL B to 5.5 MHz, so that the mixture is always formed the sound intermediate frequency of 5.5 MHz.
International agreed to operate in a sufficiently wide range around the usual intermediate frequencies not powerful transmitter that would generate heavy collapsible disorders. These could be ( at least in the vicinity of these transmitters) eliminated only by extremely effective resonant circuits or tuned precisely balanced mixer.
In wideband receivers and radio scanners first intermediate frequency is often larger than the highest reception frequency to despite insufficient pre-selection to achieve a sufficiently high image frequency spacing.
In LNBs can be found intermediate frequencies in the range of 950 MHz to 2150 MHz, and also the frequency of the local oscillator is fixed. The frequency reduction is only performed in order to transmit the deeper ZF via a coaxial cable can.
For professional radio equipment, a multi-stage signal processing is often used, also unusual intermediate frequencies are used. The first intermediate frequency may be 10.8 MHz, the second IF frequency of 450 kHz to 470 kHz are used.
After amplification, the intermediate frequency is supplied to the respective demodulators or Doppelsuperhetempfängern other mixers.