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.
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.
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 dBuV |
Max level dBuV |
Carrier to Noise db |
|
|---|---|---|---|
| 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
Why DTT is different from an analogue install
Ref 1 ITU-R PN525-2 available here
Ref 2 RSGB Radio Communication Handbook p11.3
Ref 3 CAI Code of Practice, May 2000