Transmitters and recievers Flashcards
This is the concept of a transmitter
This is the concept of a receiver
RF Front-End is critical to performance. Inductors and Capacitors create selectively tuned circuits
Detection circuits for decoding AM and FM are different
Modulation refers to how audio or data information is superimposed onto an RF Carrier Frequency
The RF carrer is a sign wave
Amplitude Modulation
The audio signal varies with the aqmplitude of the RF Carrier
If Audio is too strong clipping and distortion occurs
Simple AM gives carrier with lower and upper sidebands.
The audio signal varies the Frequency of the RF carrier- The amplitude stays constant
Actual amount of variation is small and called deviation
Signal Amplitude is constant and doesn’t carry infro an is therefore less prone to inteference
CW & FSK modulation
It is the simplest form of digital mode
Frequency Shift Keying is used for higher speed packet dates
Earthing/EMC
Good reception escpecially on HF as well as EMC (Electromagenetic Performance depends on Good Earthing)
Ensure shack equipment is run from a common mains Earth to prevent Earth loops - use filtered mains boards and ferrite rings correctly
RF Earths for antennas are often seperate - consider Earth Stakes
Modern Gas & WAter Pipers can give high resistance Earth
AM/SSB can be rectified /detected easily, so is most prone to cause inteference - operate in a responsible manner.
Operating Precautions
Ensure transmitter frequencies/modes are setup correctly so emissions are alwaqys in band and conform to band plans.
Ensure Transmitter Frequencies/Modes are setup correctly so emissions are always in band and conforms to band plans.
RF power amplifiers outputs must be connected to a correctly matched antenna to . Use of the wrong antenna can results in damage to the transmitter
Excessive AM modulation or FM deviation will cause distorted outputs and inteference on adjacent channels
Ensure microphone gain (where fitted) is correctly adjusted
