Signal Jammers are a collectible in GTA Online, added with the Diamond Casino Heist update. They are scattered throughout San Andreas. For their destruction, you will get a total of GTA$150,000, 50,000 RP, and Avi Schwartzman will become available as support crew the Diamond Casino Heist.
Their locations on the map are shown below. You can track how many jammers you have destroyed via the Inventory section of the Interaction Menu.
Destroying jammers can be difficult for beginners, as often they are located high and/or in hard-to-get-to places.
In addition, their render distance is extremely low. Therefore, in some cases, you can’t do without a sniper rifle or aircraft.
Jammers #35 and #50 are the most difficult cases.
Signal Jammer #35
It’s located in the Bolingbroke Penitentiary. If you have an armored car, Oppressor MK II, or other similar vehicles, then there should be no problems.
Otherwise, you will have to fight your way into the prison territory and try to destroy the jammer before the guards shoot you.
There is also a building outside the prison, from the roof of which the jammer is visible through a sniper rifle scope. But you can get there only using some aircraft.
Signal Jammer #50
It’s located at the top of the control tower in Fort Zancudo.
If you own a hangar in the fort, just destroy the jammer in any convenient way. Otherwise, you will be attacked by the soldiers and get 5 wanted stars.
If you don’t have any special vehicles, it’s best to jump over the fence with a fast car or motorcycle, as shown in the screenshots below.
Then you will need to drive as close to the tower as possible and destroy the jammer with a sniper rifle. After that, it’s quite difficult to survive, but you can try to fly away using a fighter, as in the daily objective.