30-04-2014, 04:08 PM
Foundation Course Transmitters & Receivers
Foundation Course.ppt (Size: 250 KB / Downloads: 61)
Tuned Circuits
Radios depend on the concept of tuned circuits.
Tuned circuits are built from combinations of Inductors and Capacitors which have a self-resonant frequency.
Tuned circuits are thus able to selectively pass or block frequencies in transmitters and receivers.
They are the basis of tuners, filters, oscillators, ATUs etc.
Earthing/EMC
Good reception especially on HF, as well as EMC 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 separate - consider earth stakes etc.
Modern Gas & Water Pipes can give high resistance earth.
AM/SSB can be rectified/detected easily, so is most prone to cause interference - Operate in a responsible manner!
Operating Precautions
Ensure Transmitter frequencies/modes are setup correctly so emissions are always in band, and conform to bandplans.
RF power amplifier outputs must be connected to a correctly matched antenna to work properly. Use of the wrong antenna can result in damage to the transmitter.
Excessive AM modulation or FM deviation will cause
distorted outputs, and interference on adjacent channels
Ensure that Microphone Gain (where fitted) is correctly adjusted