Strange RSSI and Jitter Issues - low thruput


I have a link with BH20 over 26km. (15.9miles)
Rssi is usually about 1000, jitter 7-9 (as i know, it’s normal at bh20 configuration) radio level is about -62 at master side, and about -67 at slave side. Thruput is 100% in most of the times, but sometimes, rssi goes down to 7-800, jitter also rises, for example the radio level is -77 at the moment, so i have to switch back to modulation level2 (10mbps).
master side is about 50m, slave side is about 28-30m. no more than 15m height trees on the way, topo is flatland. there is a two lane road between the two cities on the radio path.

Anyone has idea?

ps: oh, yes, i tried freq 5735, 5770,5785,5805,5820,5840 and unit is set to 5815 now. all the same…

Which firmware are the BH running??

A 26km/5.7GHz link needs 13m for earth curvature and 9m for the Fresnel zone; 22m combined at the midpoint. Adding 15m trees in the middle makes the minimum antenna height 37m at each end.

You should be good with 30m and 50m antennas unless the elevation is neither flat nor a constant grade up or down. If the problem is worse when the wind blows or it’s raining, the cause could be the trees extending into the Fresnel zone.

Well, avg RSSI from end of July (when we have installed the link) to end of May, is 1150, Avg jitter is 7.

Avg rssi in last 5 weeks is 1065 and jitter is 5.92 (i have turned the modulation down on the last week).

The strange: in the night, the signal is better with 1-200 rssi than daytime
(rssi is much better in 8pm-7am period)

The area is flatland, with not high rain zone.

I can raise from 50m to 60 if it’s a must, and other side too with another 3m
(if it could help a lot)

Thanks for any ideas

The fact that the link’s performance varies with time-of-day could indicate interference. Run the Spectrum Analyser from both ends at different times of the day.

Raising the reflectors at both ends could make a difference, but there’s no guarantee.