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# TV UHF VHF signal current voltage and power generating in TV antennas

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#### isurunalaka

##### Member level 5
dear all

does anyone know about the current and voltage ranges generating in TV antennas by TV UHF and VHF channels? or power?

The biggest UHF TV transmitter I know uses 10 off 50 KW peak sync power, i.e. 500KW. The input to the aerial will be 50 ohms. So V^2/50 = 500,000 so V = 5,000 and the current 100A. This is a problem for the aerial feeders as the coaxial cable has to withstand this voltage so it has to be very large in diameter. if its very large in diameter, the the RF treats the gap between the inner and outer conductors as a wave guide if the frequency is too high.
The smallest TV transmitter is about 1W for filling gaps in coverage due to shadow effects in valleys.
Frank

isurunalaka

### isurunalaka

Points: 2
The biggest UHF TV transmitter I know uses 10 off 50 KW peak sync power, i.e. 500KW. The input to the aerial will be 50 ohms. So V^2/50 = 500,000 so V = 5,000 and the current 100A. This is a problem for the aerial feeders as the coaxial cable has to withstand this voltage so it has to be very large in diameter. if its very large in diameter, the the RF treats the gap between the inner and outer conductors as a wave guide if the frequency is too high.
The smallest TV transmitter is about 1W for filling gaps in coverage due to shadow effects in valleys.
Frank

you are talking about transmitter. But i was referring to the power generates in TV antenna at the receiver for UHF and VHF.

you are talking about transmitter. But i was referring to the power generates in TV antenna at the receiver for UHF and VHF.
Should say you are thinking of receiver antennas but didn't actually tell that.

Minimal Voltage, current and power range can be estimated from TV tuner sensitivity numbers. Something like 100 µV should already gives good quality. Current and power can be calculated according to 75 ohms charcateristic impedance.

isurunalaka

### isurunalaka

Points: 2
If want to go deeper, the analog TV needs a minimum of about -75dBm (50uV/75ohms) at receiving antenna, when digital television needs a minimum of about -82dBm (22uV/75ohms).

isurunalaka and FvM

Points: 2

### isurunalaka

Points: 2
if 50uV signal is appear on 75ohm antenna, how much power/current does generate on antenna? how to calculate? what is relationship between P, V and I for these signals?

The same ones it always is,

P=V*I = I^2R = V^2/R and so on.

For maximum power transfer the load impedance is the same as the characteristic impedance of the aerial circuit, 75 ohms in this case, and the 50uV is probably measured with a 75 ohm termination present.

So power is simply ((50 * 10^-6)^2)/75 = 33*10^-12 Watts = 33nW.

Note also that this is (in old school telly speak) peak sync power, so you are probably looking at lest 10dB below that for average power.

Regards, Dan.

isurunalaka

### isurunalaka

Points: 2
So power is simply ((50 * 10^-6)^2)/75 = 33*10^-12 Watts = 33nW.

You had a typo: that is only 33 pW

isurunalaka

### isurunalaka

Points: 2
Whoops, yea.
**Small** numbers anyway....

Regards, Dan.

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