In radio transmission there is no substitute for power, both on the jamming side as well as on the side that wants to get their message through.
20 dB is a big deal because it would make the jammer a lot harder to locate, especially if it times its interruption well and can get away with extremely short bursts of activity followed by relatively long periods of silence.
Other tricks of the trade: jam from multiple locations with short bursts, slap the jammer right under the nose of the receiver that you want to jam (that way you need a minimal signal and are almost impossible to detect at range until you're right up to it).
This is the way TV pirates in Amsterdam would broadcast their signals in the 80's to the receiving dishes on Hotel Okura. They were so low power and right up close to the dishes that they could push legitimate broadcasts (mostly German TV) right out of their slot. KTA (the then monopolist on Cable TV in Amsterdam) had the un-enviable task to come up with a solution and finally settled on a system where if one antenna was flooded with a rogue signal they would switch to antennae mounted on a chimney of the electricity plant on the other side of the city (Amsterdam had very little high buildings).
Of course, pirate TV stations found out about this quickly enough and located another transmitter near there and so on.
20 dB is a big deal because it would make the jammer a lot harder to locate, especially if it times its interruption well and can get away with extremely short bursts of activity followed by relatively long periods of silence.
Other tricks of the trade: jam from multiple locations with short bursts, slap the jammer right under the nose of the receiver that you want to jam (that way you need a minimal signal and are almost impossible to detect at range until you're right up to it).
This is the way TV pirates in Amsterdam would broadcast their signals in the 80's to the receiving dishes on Hotel Okura. They were so low power and right up close to the dishes that they could push legitimate broadcasts (mostly German TV) right out of their slot. KTA (the then monopolist on Cable TV in Amsterdam) had the un-enviable task to come up with a solution and finally settled on a system where if one antenna was flooded with a rogue signal they would switch to antennae mounted on a chimney of the electricity plant on the other side of the city (Amsterdam had very little high buildings).
Of course, pirate TV stations found out about this quickly enough and located another transmitter near there and so on.
I have all this info from hearsay, cough.