SM external gain

I've been trying to find some info. on what the appropriate numbers should be set to for the external gain on our 450 SM's. When we switched to the 450 system, we were told to put the external gain to 17db when using a reflector/dish.This was when we only had the 3.65 Ghz frequency and not the 5.8. We've since added the 5.8 and have used the same 17db gain. From what I've read on this issue is that if it's too high or too low, you could be causing yourself some issues and the numbers I've seen/read are that the 5.8 SM's with reflector should be set to 15 or 16 and the 3.65 SM's should be 11 or 12. So if we are setting them to 17, were are probably hurting ourselves and could be part of the speed issues we get reported to us every once in awhile.

So my question is, what should the external gain be for a 450 5.8Ghz SM and 3.65Ghz SM with reflector/dish?

Spec sheets say reflector adds 16 dB (5 GHz) or 12 dB (3.65 GHz).

But I don't think the setting would impact your performance in 5.7 GHz.  In 5.4 GHz there is an FCC limit of 30 dBm EIRP, and in 3.65 GHz under Part 90 there is a 30 dBm per MHz limit.  Under CBRS the power limit will be dictated by the grant from the SAS.

In any case it would only be the uplink speed that would be affected.

At the AP end a wrong antenna gain can cause problems with false DFS or LBT events, if the gain is set lower than the actual antenna gain.

Cambium has been moving to integrated antennas on the SMs, in which case the antenna gain is hard coded, you can't change it.

2 Likes

In addition, not having your External Gain set accurately might result in close SMs having trouble registering to the AP. As the SMs try to hit the "SM Receive Target Level" even on the Registration Request, and if it is too far off the AP might reject the Registration Request.