Transposer
In
Physical obstruction
Reception of
Translator circuitry
Broadcast station transmitters have the following stages:
- Audio (AF) or video (VF) frequency buffer stages
- Modulator
- IF stages
- Mixer (IF → RF)
- RF output stages (amplifiersand filters)
FM and TV translator stations have the following stages.
- RF input stages (RF amplifiers with AGC and band-pass filter)
- Input mixer (RF → IF)
- IF stages
- Output mixer (IF → RF)
- RF output stages (RF amplifiers and filters).
The output stages of both devices are similar, but the input stages are quite different. There is no baseband audio or video input to the translator. The translator receives an over-the air RF input signal by means of an antenna, just like a home receiver. Since received signal is already modulated there is no need for a modulator. Instead an input mixer or down-converter shifts the radio-frequency (RF) signal down to an intermediate-frequency (IF) signal. A second mixer (known as output mixer or up-converter) shifts the IF signal back up to the FM or TV band output signal frequency.
Relationship between input and output RF signals.
In order to stabilize the output power, the amplification of the input RF signal is automatically controlled by PIN diodes [2] If the frequency of the output signal were to be set equal to the frequency of the input RF signal, the output RF would feed back from the output antenna to the input antenna and the input stage would overload, completely blocking out the translator. Because of this, the translator output frequency must be different from the input signal frequency.[3] Input and output band-pass filters further isolate the two signals.
Future of the translator
In North America FM and TV translators were common before
With the operation of an FM or TV translator being less expensive than the same power full-service station they remained an attractive signal delivery alternative.
The transition from the analog
The introduction of In-band on-channel (IBOC) hybrid analog digital FM (HDFM) technologies provided further opportunities for translator system operators.
See also
- Broadcast relay station
- TV transmitters
- Transmitters
- Output power of an analog TV transmitter
- Radial (radio)
- Earth bulge
References and notes
- ^ R.Busi: High Altitude VHF and UHF broadcasting stations, European Broadcasting Union, Bruxxeles,Brussels, 1967, p. 93.
- ^ The level of the incoming RF signal can fluctuate greatly, depending on weather and other factors.
- ^ With television translators, for example, a difference of at least two channels is required.