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How Much Separation Is Required Between Inside & Outside Antennas?

We get asked frequently how much separation is required between interior device antenna, and exterior tower antenna? What happens if it is less?

Signal feedback (otherwise known as oscillation) can interfere with the cell tower, and that is why it is vitally important that there’s proper antenna separation. This separation between antennas is a straight-line measurement from the closest interior antenna to the exterior antenna.

Please note that the stronger the outdoor cell signal, the more separation is required. Less separation may be sufficient for less cell signal. There are a number of factors that determine the closest allowable distance, and these include building materials, amplifier dB gain level, and so on. Please see below for the recommended separation distances.

Booster Gain (dB) Minimum Separation:

20 dB booster = 2 ft. to 3 ft.

30 dB booster = 4 ft.

40 dB booster = 6 ft.

45 dB booster = 15 ft.

55 dB booster = 55 ft.

65 dB booster = 70 ft.

68 dB booster = 80 ft.

70 dB booster = 110 ft.

80 dB booster = 125 ft.

Above separation recommendations are general and may vary depending upon the materials between the two antennas (inside antenna and outside antenna). Sometimes the separations have thick concrete between them and therefore will not require a lot of separation. Sometimes the separations only have a little drywall type material betwen the donor antenna (exterior) and the receiving antenna (interior). Amplifier itself will be the best indicator because it will confirm with its indicator lights whether separation is enough or not.

What do each color cell phone signal booster indicator lights mean? Alternating red and yellow lights mean that external and internal antennas are too close together and they are causing something called an oscillation or feedback loop. This is when you can increase the distance between both antennae.

What is MRSD? How do I ensure its compliance?

Signal boosters each have specific Minimum Required Separation Distance (MRSD) requirements that determine the distance between antennas. This requirement must be adhered to for the booster to work properly.

You will find the MRSD for your specific booster model in the Installation Guide.

As a rule of thumb, an indoor signal booster with 50dB of gain requires 40 ft. of separation between antennas, while a booster with a 60dB gain requires 75 ft. This is an estimate only. It truly depends upon the thickness and types of materials that exist between the two antennas. 

Note that separation should be measured as a straight line between the two antennas, and not the length of cable that connects the antennas to the booster.

For vehicle boosters, it is best to place the outside antenna centered on, or toward the rear of the vehicle roof.

As the metal of a vehicle's roof acts as a shield between the antennas, antenna placement is a bit less critical for vehicle boosters.

If antennas are placed too close to each other, the booster may experience a feedback loop causing oscillation. This will cause the booster to immediately shut down to avoid damaging the mobile network. Operation will not be resumed until the issue has been resolved.

A red light will typically be displayed on a signal booster to indicate that oscillation has been detected. To solve the problem, move the antennas further apart.

No minimum separation distance is required between the signal booster unit and either antenna. The Minimum Required Separation Distance is only critical between the two antennas, and is critical to the booster operating properly.