Dr. McCown. If separation is important then how do they get away with
making both antennas essentially the same unit? I'm sure there is a
simple explanation.
Chuck McCown wrote:
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 <mailto:[email protected]>
*Sent:* Tuesday, February 16, 2016 9:09 PM
*To:* [email protected] <mailto:[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 <http://www.gogebicrange.net/>
