Too much gain too close to AP?

An installer of ours made an observation concerning the use of a Clip or Reflector Dish @ less than 1 mile to a particular tower.

We have tight restrictions on what we consider an acceptable signal.  We shoot for 6x or better modulation at all new installations of 450 gear even if it means adding a Clip or RD. 

He notices each time we put up an RD for OFDM to achieve 6X when the site is close to the tower he's been noticing each subsequent install to the same AP results in a lower average SNR. He thinks the proximity of the site to the tower and the use of an RD are making the area noisy.

Could this be true?

An excerpt from the "SP_Strategies_for_Migrating_2.4_GHz_PMP_100_to_PMP_450" tends to back this up, at least for 2.4 GHz:  "Because of the additional gain of the dish, the PMP 450 SM frequency response is amplified causing spurs to exceed the regulatory limits in the restricted bands at the upper and lower ends of the 2.4 GHz band."

Does something similar happen in 5 GHz as well?

Wow, you're having to use a clip or reflector at 1mile or less to even get 6x? Are you using an omni on your base station? Do you have an incredible amount of noise? What do you have your ATPC set to on the AP? We're using -60.

At times, yes, unfortunately.  Our network is a mix of Omni/Sector.  Noise is probably above average.

Our SM Receive Target Level  is -52 and very few ever get that.

Anything from Cambium RF gurus?

I have seen your question and will find a Guru to help me answer the quesiton.

The issue in the 2.4 GHz band was on how close we could get to the edge of the band without violating the emission requirements in the adjacent bands. The additional gain of the dish increased the level of spurious emission, which forced us to limit the range of center frequencies supported.  The “2.4 spur problem” cited by the customer will not be seen in the 5.8 band due to its distance from the restricted band.

It would be interesting to know the relative location of the SMs. For example, if the SM with the dish is facing the back lobe of another SM, the additional interference coming from the back lobe can degrade the signal quality of the second SM. Also, if a second SM if facing the back lobe of the SM with the dish, it will receive more interference from the front. Is this what you were referring to in your statement “lower lobe”? If the SM with the dish is very close to the AP, SMs far away will see it almost co-located to the AP, and are pointing to its back lobe.

Is the affected AP on an omni?