It should be relatively easy to spot the most common cheap jammers, but only if they are close to you. Remember that your drone will be able to receive signals within its enhanced radio coverage area that you on the ground can't
They typically transmit a swept signal, often with some additional noise component, and usually have to be at least 10 times stronger at the receiver than the signal being jammed in order to be effective.
In addition to the examples already mentioned cheap GPS jammers also tend to be used inside vehicles for various bad purposes, so these can also be problematic for genuine users, as they move around. I have noticed this myself when using a GPS satnav in my car. Sometimes it can't receive any satellites, even though the sky is not obscured. it is only when I have moved away from other traffic, and reception is restored, that I realised a jammer was probably being used in one of the other vehicles.
Regards,
Martin
