What is a transmitter?
A transmitter is an electronic device that is generally mounted in the field in close proximity to a sensor. The sensor (also known as a transducer) measures a physical variable such as temperature or pressure and outputs a very low level electronic signal. The basic function of the transmitter is to provide the correct electrical power to turn on (or excite) the sensor then to read the low level sensor signal, amplify it to a higher level electrical signal and send that signal a long distance to a control or read-out device. Since low-level electrical signals do not transmit long distances with great accuracy, installing a transmitter generally gives a tremendous improvement in the accuracy of the information delivered to a larger control system.
” Good question. A transmitter is a device that converts AC or DC energy to RF energy. By itself, RF energy doesn’t do us much good, so a transmitter also requires audio information to “Modulate” the RF energy it generates. The modulated RF energy is coupled into an antenna to be dispersed into the ionosphere. Now that you know what a transmitter does, we’re going to discuss variations and capabilities that can be found when looking for your dream rig. Controlling The Frequency In the beginning there was Crystal Control. This means you must supply a crystal cut or ground for a specific frequency to operate on that frequency. If you wanted to operate on 7415 Khz, then with a crystal controlled transmitter you would have to supply a crystal cut or ground for 7415 Khz. You could NOT operate on 7465 Khz unless you supply ANOTHER crystal for 7465 Khz.
Basically, a transmitter is a signal conditioner. It accepts a low level input signal from a sensor, a millivolt signal from a thermocouple or a resistance signal from an RTD (Pt100), and provides an output signal that is directly proportional to the input-signal. Most transmitters provide a current output signal (generally 4-20 mA or 0-20mA signal) rather than a voltage output. Conversion to a current signal virtually eliminates any interference from line noise and allows accurate transmission over relatively long distances using ordinary uncompensated copper wire. The use of expensive thermocouple wire or extension wire is no longer necessary. Transmitters are available in both isolated and non-isolated versions. Isolated transmitters are used to provide galvanic seperation between the sensor input and signal output. When grounded sensors are used or leakage to ground occurs (with ungrounded thermocouples), isolated transmitters must be used.
Related Questions
- Now we can derive from this that no 72 MHz transmitter using a bandwidth greater that 20 KHz is legal today. Although this is a good statement, how do we determine that?
- What is the difference between a short-range transmitter with an air core versus a short-range transmitter with a ferrite core?
- How many receivers can be linked to an Eos base station/transmitter?
