# What kind of signal modulation is more resistant to jamming?

I've understood that spread-spectrum type of modulations are more resistant to narrow band jamming, for obvious reasons. What is less obvious is why someone would try to jam for example a cellular phone, GPS or ADS-B (Mode S) transmitter using a narrow-band jammer? (Whatever "narrow" or "wide" means in this context?)

What are the criteria and essential details for a jamming resistant modulation?

EDIT:

I have since understood quite a bit more about this topic. A wide-band jammer would spread all its energy over the entire spectrum of frequencies it tries to cover. This is extremely energy consuming and thus due to the inverse-square relation for radiation, you quickly loose energy with distance, so narrow-band beam formed jamming is preferred. However, narrow band jamming is weaker since certain frequency hopping methods can be applied to foil the jamming.

• Would appreciate if someone could add jamming and interference to the TAG pool. – not2qubit Jul 7 '17 at 21:34
• The short answer is that designing wideband transmitters is very hard. – MBaz Jul 7 '17 at 21:56
• @MBaz Wideband transmitters are very easy to design. But I dare say you mean legal ones. :-) – Peter K. Jul 7 '17 at 22:07
• @PeterK. True :) But I'd counter that designing a spark-gap transmitter that generates a large frequency and reaches more than a couple km is still very hard. Do you know what's the maximum frequency reached by a spark gap? I thought it was a few tens of MHz at best. – MBaz Jul 7 '17 at 22:16
• @PeterK. Indeed -- but with an antenna 60m high and a gap voltage of several tens of thousands of volts, it doesn't fit my definition of "easy" :) I seem to recall that Marconi's transmitter operated at a center frequency of 1.2 MHz. – MBaz Jul 7 '17 at 22:38