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Field strength calculation according to ITU-R PN525-2

Enter your values here to get an estimate of field strength for your distance to the transmitter. You must have a clear clear line of sight to the transmitter. If you don't all bets are off and this calculator is absolutely no use to you whatsoever.

Note that your results will be of the order of 10-20dB lower than this predicts. To get the signal strength predicted by this calculator your antenna must be several metres higher than surrounding obstructions, house roofs etc and have a clear line of sight to the transmitter. Most domestic installations do not satisfy these requirements, hence assume at least 10dB lower signal levels.

TX e.r.p. (kW)
distance (km)
UHF channel
frequency (MHz)
path loss (dB)
field strength (V/m)
RX antenna gain (dBd)
signal @ aerial terminals (dBuV)
Masthead amp gain (dB) (0 if none)
Downlead length (CT100) (m)
signal @ aerial terminals (dBuV)

The example values are those for my antenna installation, which is a roof level antenna off a gable end with a clear  line of sight to Sudbury. I measure a signal level of 71-74dBuV for channel 44 using a Promax cable analyser which is 10-13dB lower than predicted. Which is reasonable given the typical domestic installation.

How it works - worked example and references for the calculation.

the obvious FAQ:

Q: I get nowhere near that much signal level. What's up with that then?
A: You don't have line of sight, or nearby obstructions, trees get in the way. If your aerial is in the loft, there is a loss of 5-25dB going through a typical tiled or slate roof, and you most certainly are suffering an extra loss due to proximity to water tanks and clutter which can knock another 5-20dB off your signal level.

How much signal do I need?

It all depends on what you're trying to receive.. Here are the recommendations from the Confederation of Aerial Installers Code of Practice3 We're assuimng UK practice and a cable impedance of 75 ohms here.

  Min level
Max level
Carrier to Noise
Analogue TV PAL I 60 80 43
Digital UHF DTT 45 65 26 @ outlet
30 @ aerial
FM (stereo) 57 74 45
FM (mono) 40 74 25
DAB (Band II) 45 70 20
Sat IF analogue 47 77 15
Sat IF digital 47 77 12

Selecting and siting your TV aerial

Aerial system components

Why DTT is different from an analogue install


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Ref 1 ITU-R PN525-2 available here

Ref 2 RSGB Radio Communication Handbook p11.3

Ref 3 CAI Code of Practice, May 2000

M E g A L i T h i A
Text and photographs Richard M 2003 unless otherwise credited