Handy rules of thumb
The decibel (dB)
Compared to ordinary numbers dB-values are slightly different, because they are logarithmic and represents ratio’s (divisions or multiplications).
But the following examples might help for power values:
| 0dB = power x 1 | |
| 3dB = power x 2 | -3dB = divide by 2 (power x 0,5) |
| 6dB = power x 4 | -6dB = divide by 4 (power x 0,25) |
| 9dB = power x 8 | -9dB = divide by 8 (power x 0,125) |
| 10dB = power x 10 | -10dB = divide by 10 (power x 0,1) |
| 20dB = power x 100 | -20dB = divide by 100 (power x 0,01) |
| 30dB = power x 1.000 | -30dB = divide by 1.000 (power x 0,001) |
| 40dB = power x 10.000 | -40dB = divide by 10.000 (power x 0,0001) |
Still a bit difficult, this website will do the math for you:
www.rapidtables.com/electric/dBW.htm
Determining transmitter power
How powerful will my transmitter have to be with the antenna gain of my system with 100 Watts antenna input (transmitter power decremented with the antenna cable loss)?
You will find the answer here:
www.csgnetwork.com/antennaecalc.html
Make sure you enter the amplification factor of your antenna in the correct unit !
Usually manufacturers provide the antenna gain in dBd, but it can also be specified in dBi.
Simply add +2.14dB to the dBd-value to get the gain of your antenna in dBi.
Or substract 2,14dB from the dBi-value to become the dBd-value.
Because with dBi one takes an isotropic antenna as reference, with dBd one refers to a lambda/2 dipole, that ratio is always 2.14 dB.
Calculate intermodulation products
Two transmitters on the same antenna tower without filters, is not a good idea. You will almost certainly get intermodulation products.
You can calculate at which frequencies these products will occur with the tools on the following website:
www.arcticpeak.com/radiopages/intermodulationproducts.htm
Line of sight calculations
These can be done with the tool on the following websites:
www.everythingrf.com/rf-calculators/line-of-sight-calculator
RF calculator
On the following website you will find a handy “RF-calculator”:
radiomobileonline.pe1mew.nl/?RF_Aids:On-Line_Calculators: RF-Calculator
DAB/DAB+ capacity units calculator
Check how many services you can broadcast in one MUX: