ePMP 4600 - Odd Issue with SM mounting height and signal

[terintamel]

I am fully aware and have run into periodic issues before with my AirmaxM/AC and even Canopy PMP100 equipment before where they would experience periods of signal issues due to usually crop induced thermal fade.

However, I went out today to upgrade a customer from an PBE-5AC-Gen2 to an ePMP 4625 and was not able to do it as the signal I got at the mount location of the PBE was too weak for our standards.

The PBE gets a -55db signal at 2.3 miles. Based on calculations I expected around a -60 to -61db RX signal for the 4625. What I got though was an RX signal of around -69 to -72db.

I am using the Cambium 4x4 antenna for the 4600 AP and used a digital level to make sure it was within .25deg of being plumb.

I am in pretty flat farmland so the changes in elevation of the terrain along his path is pretty minimal.

His mount is around 10-11ft up on the side of his house just under the eave. What I found odd is that if I lowered the dish to around 6ft I got a -57db. If I raised the dish to around 12-14ft I got a -57db, but anywhere from 7-11ft I got worse signals. At 7ft is was around -63db and as I continued to go higher to the existing mount height the signal got worse until I was a few feet above the mount height.

Photo of mount. Red box is around height where I got great signal.

I tested again away from the house and 6ft farther to the west (left) using an 8ft A-frame ladder and got the exact same results.

Is this because of the snow or does the 4x4 antenna have some type of dead spot in its elevation pattern that I just happen to hit at the mount height of this customer?

Here is his current view of the tower taken today.

[Eric_Ozrelic]

Is the SM at boresight of the 4x4 antenna or are you on one of the edges? Did you take into account that the OEM antenna has -2deg of electrical tilt?

While the 4x4 OEM antenna claims to be for 90deg use, we’ve had best experiences with it when we treat it like a 60deg antenna.

[terintamel]

It is not an issue with the azimuth of the customer but the elevation. Customer is around 5deg from being directly straight south from the south facing AP so the azimuth pattern of the AP is not the problem.

Yes, I am aware of the -2deg tilt of the AP antenna. Would make more sense that being the issue if only lowering the height of the SM would improve the signal, but also increasing the height of the SM has the same affect on improving the signal.

At 2.3 miles the -2deg down tilt should not be much of a factor in my calculations. I would expect it to be an issue either much closer to the tower or much farther away.

[terintamel]

So if the signal improves if I go lower than the 10-11ft mounting height or higher than the 10-11ft mounting height is that an issue with the tilt of the AP or something else?

I believe when I put up the AP I used a digital level and it was either plumb or had around 0.25deg of uptilt.

In the past with UI antennas I would add some manual uptilt of around 1deg or so as it seemed to give better signals to my farther clients this way, but the tilt never seemed to cause an issue where the client’s signal would be improved by moving the SM either higher several feet or lower several feet. I would find clients who either needed to go higher or they needed to be lower, but never one where higher and lower gave the same results.