TV TRANSMITTERS: POWER MEASUREMENT
sually it is defined “TV Transmitter power” the RMS (effective) power provided during the
sync transmission (W p.s.). This is right for the most common transmission standards: the
ones with negative modulation (B, G, D, K, I, M, N).
For an exact power measure, it is necessary to use a wattmeter which can measure the effective
power during the modulation peak envelope (PEP) and which is qualified to give a right measure
even thought the short length of the peak envelope represented by the sync pulse (eg. BIRD
Mod. 4391).
If you use common wattmeter, which measure the medium effective power (eg. BIRD Mod. 43),
the reading will be lower (even less than 50%) and affected from negative video modulation.
If you don’t have a proper wattmeter, in the case of an alternate way of measuring, for example
by the comparison of the modulated or non modulated carrier, you have to remember that:
¨ TV transmitters, particularly high power ones, aren’t often expected to be used at full
output power without video modulation. If you use the transmitter this way, even for a
short period of time, you can damage the power amplifier
¨ TV transmitters have an automatic reduction of the output power in case of absence of
sync. It can mispresent an eventual comparison.
¨ If you use directional couplers, attenuators, spectrum analyser, you must be sure of the
instrument’s precision and tolerances, because in a lot of measure you can easily do
mistakes of some decibels, wich can completely affect the measure. An error of 3dB,
wich can easily be made by this way, correspond to read the half or the double of the real
power.
sually it is defined “TV Transmitter power” the RMS (effective) power provided during the
sync transmission (W p.s.). This is right for the most common transmission standards: the
ones with negative modulation (B, G, D, K, I, M, N).
For an exact power measure, it is necessary to use a wattmeter which can measure the effective
power during the modulation peak envelope (PEP) and which is qualified to give a right measure
even thought the short length of the peak envelope represented by the sync pulse (eg. BIRD
Mod. 4391).
If you use common wattmeter, which measure the medium effective power (eg. BIRD Mod. 43),
the reading will be lower (even less than 50%) and affected from negative video modulation.
If you don’t have a proper wattmeter, in the case of an alternate way of measuring, for example
by the comparison of the modulated or non modulated carrier, you have to remember that:
¨ TV transmitters, particularly high power ones, aren’t often expected to be used at full
output power without video modulation. If you use the transmitter this way, even for a
short period of time, you can damage the power amplifier
¨ TV transmitters have an automatic reduction of the output power in case of absence of
sync. It can mispresent an eventual comparison.
¨ If you use directional couplers, attenuators, spectrum analyser, you must be sure of the
instrument’s precision and tolerances, because in a lot of measure you can easily do
mistakes of some decibels, wich can completely affect the measure. An error of 3dB,
wich can easily be made by this way, correspond to read the half or the double of the real
power.
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