14. Transmitter Measurement

Definitions

Decibel is used as a comparison. It can either be a comparison between two measurements or between one measurement and a standard unit.
0 dBW does not mean there is zero power, but it means the power is exactly the same as the reference, 1 Watt, in this case
3dB down is the bandwidth usually quoted to be the frequencies between the half-power points
Two Tone Generator comprises two audio oscillators whose out puts are combined into a single output to be connected to the microphone input of the transmitter under test
Mean power output of an SSB transmitter fed with two tones will be 50% of the Peak Envelope Power
Effective radiated power (ERP) is an IEEE standardized definition of directional radio frequency (RF) power transmitted from a theoretical half-wave dipole antenna
Peak envelope power (PEP) is the highest envelope power supplied to the antenna transmission line by a transmitter during any full undistorted RF cycle or series of complete radio frequency cycles
Net happens when more than two Amateurs are in conversation over the radio
Radio transeiver is a combination of a radio transmitter and a radio receiver
PTT (Push To Talk) or MOX (Manually Operated Transmit) or VOX (Voice Operated Transmission) are 3 different types of modes to change from listen to speak (receive to transmit)

Gain = 10 log (output power / input power) where Gain is in dBW, output power and input power is in Watts
Gain = 20 log (output voltage / input voltage) where Gain is in dBV, output voltage and input voltage is in Volts
Gain = 20 log (output current / input current) where Gain is in dBV, output current and input current is in A
Gain = Gain(1) + Gain (2) - Cable loss where Gain is total gain of 2 amplifiers put together in series one after another
dBW = 10 log Watts
3db down on X = X/2 where X is power in Watts

It can either be:
- comparison between two measurements
- comparison between one measurement
- standard unit
BEL was named after the inventor of the telephone Alexander James Bell
it was found that this unit was too large, so it was divided by ten
Hence deci Bel and is usually abbreviated to dB
human ear operates in a logarithmic fashion
Decibel therefore follows a logarithmic law
3dB is doubling of power
-3dB is halving of power
Advantage: Losses and gains can be added / subtracted
decibel is not just used for power comparisons and measurements but current and voltage too
Decibels are often used as the scale for response measurements

fully amplitude modulated by a sine wave audio tone
radio frequency is very high compared with the audio frequency
individual RF cycles may merge into each other on the screen and just appear as a green “modulation envelope”
carrier now varies between zero and twice the amplitude of the original (unmodulated) carrier

SSB transmission only contains one side band
other sideband has been eliminated and the carrier has been suppressed
very important to ensure that the various frequencies contained in the remaining sideband do not inter-modulate (mix) with each other
other unwanted frequencies (intermodulation products) would be generated and transmitted
very undesirable and must be avoided at all costs otherwise considerable interference will be caused

three main types of radio communication:

Speech - via microphone
Morse - via Morse key or keyer (automatic or semi-automatic)
Digital - via keyboard on teleprinter or computer Procedures for each of these types will be explained.