Antenna placement

Placing device inside a metal building - Antennas placed outside via two 20’ LMR 400 cables - how far above the roof should the antennas be placed? Is there a prescribed min separation between the antennas? How do I locate the direction to the cell tower?

If the roof is metal, I would suggest as high as you can go. The reason for that is that the RF energy will be reflected off of the metal roof. The higher up you are from it, the less affect it will have.

Minimum separation of the antennas is function of the maximum output power of the radio and antenna combined. However, a good rule of thumb is to keep high gain antennas at least 10 ft apart.