Hi Rob,

A while ago I asked you about an AF interference issue. Well I’ve just solved it – and it was not at all what was expected.

Background:

2 AF P2P links, similar path with about 1m vertical separation and 20 degree separation at site ‘A’ of the 2 links.

Link 1 – Site A-B

Link 2 – Site A-C

(There is also a B-D and C-D for backup too – RocketTi)

Both links are about 1km.

Link 2 was exhibiting packet loss, but not link 1.

What we tried:

1/ replacement of all cables

2/ replacement of both Link 2 AF units

3/ factory resets

4/ using half duplex links of different frequencies

5/ firmware (1.5)

6/ GPS sync on link 1 and link 2

7/ change RX gain from high to low and low to high

8/ reduce power to about 8db (20 being normal)

9/ increase of vertical separation between site A AF units

10/ & the winner! At site C – move the AF closer to the edge of the building.

Where the AF at site C was, it was too close to the roof and too far from the edge – this image kinda explains it:

What I determined (reading, reading, theorizing, thinking and frankly smashing my head into the desk) was that we were seeing multipath or reflections from the roof top: (also the roof was corrugated tin and aligned in such a way that would cause this..)

So the fix? We moved it to the extreme edge of the roof.

And the results after some testing- as you can see much the loss is now gone. As at about 6am today we moved to a backup path, Site A-B-D-C which is where you can see the jitter ETC and about 12:20 today we did some tests with no joy. But from about 3.15pm onward its FINNALY all good. This has been an issue for me for over 3 months now…

The bottom line and what you should make people aware of is that the vertical “beam width” is far more significant than expected, additionally so is the aperture for RX on vertical too.

Regards,

Tom Berryman

I.T. Systems Engineer

Connectivity IT // Director

Phone: 1300 22 46 00

Email: tom@connectivityit.com.au