Somewhere, in one of my 50 or so antenna books, there is a graph showing mutual coupling of yagi antennas mounted on the same mast with respect to separation. Right now, I am 50 miles away from those books.
As I recall, if they are cross polarized, there is very little coupling at close distances. I think there is theoretically zero coupling of the far field. But you get strong reactive nearfield effects at 900 MHz around the 7 inch range or less. That just means that the two antennas will start throwing off the impedance and resonant frequency of the other one the closer they get. However there is the Radiating Nearfield Distance too. If you are inside that limit the two will mess with each others patterns pretty bad. That is on the order of 22 inches. However due to being cross polarized the effects should not be strong. So, yeah... 2 feet is good if cross pol. I don’t think I would not go under 1 foot. If you have some time, experiment a bit. From: Brandon Yuchasz Sent: Tuesday, February 16, 2016 9:09 PM To: [email protected] Subject: [AFMUG] 450i 900 using existing yagi Since we are now deploying some 450 900 gear we are pulling down lots of old FSK with M2 Yagi antennas. In general I really like the Cambium yagi they are well thought out and the SM being mounted on it is really clean. Swaps are a breeze. That said I am still thinking about using the M2 in specific situations like tripods. I did some retrofitting today to convert two to slant and we went and tested and got good results. There were separated from each other vertically about 8 inches at the mounting brackets and I didn’t see any issues . We got 8x8x line of site. So my question to the group is, in general is there a rule of thumb to use for vertical separation on dual polarity antennas being mounted like this? Could they be stacked tight near each other? Best regards, Brandon Yuchasz GogebicRange.net www.gogebicrange.net
