How much separation distance is required between the outside antenna and the inside antenna?

It depends. Each weBoost signal booster has a specific Minimum Required Separation Distance between the tower antenna and the device antenna that MUST BE STRICTLY OBSERVED. 

To find the MRSD for your specific booster model, refer to the Installation Guide that came with your booster.

As a general rule, the inside antenna and the outside antennas need 20 feet vertical OR 50 feet horizontal separation. If those distances are not feasible for your application, it can be achieved by doing a combination of the two (E.g, 10 feet vertical AND 30 feet horizontal).

PLEASE NOTE: Separation is measured as a straight line between the two antennas. Separation is NOT measured by the length of cables that connect the two antennas to the booster.

For a vehicle booster installation, it is best to place the outside antenna towards the rear of the roof on the passenger side.

The metal roof of your vehicle acts as a shield between the two antennas, making antenna placement a bit less critical for vehicle boosters.

If antennas are placed too close together, the booster may experience oscillation. Oscillation occurs when the antennas pick up each others signals and create a feedback loop.

When this happens the booster will begin to reduce its gain to prevent damage to the mobile network, and will not resume optimum operation until the separation distance issue is corrected.

Typically, a solid red light displayed on a weBoost signal booster indicates that oscillation has been detected and the booster is shutting down completely as a result. If this occurs, increase the straight-line distance between the two antennas.

If the booster displays a flashing red and green light, the booster is indicating that oscillation is being detected, but it is most likely still performing at a satisfactory level. If the booster is working, no adjustments need to be made. 

The signal booster unit itself does not require minimum separation distance from the outside antenna but does need a 18 inch to 24 inch separation from the inside antenna. The Minimum Required Separation Distance is mainly observed between the two antennas, as it is critical to your booster's continued operation.