To explain
Nominal attenuation @ 1000MHz = 20.82dB

The lower that number, the less loss and the higher grade (also expensive) the cable. 3 dB means that you lose a barely noticeable amount, 10 dB means that you lose 1/2 the power. The dB scale is logarithmic - so each dB is 10 times the power of the previous. If you have a low or bad signal - old aerial/cable downlink you may not have enough signal at the end of a very long run for a digital signal - but I'd first suspect the cable not put together correctly.