Negative noise margin and still a connection????

RouterOS Wireless Networking
1

I ordered a couple of these and gave them a try:

http://www.wifihw.cz/p312-b-5g23box-b-smerova-panelova-antena-23dbi-s-integrovanym-outdoor-boxem/?lang=eng
5G23Box.jpg
On one location I had an ok signal (-80) at 5240 with an RB711 but big problems with noise floor jumping between -110 and -80 thus causing the client to connect and disconnect every few seconds.
Problems were solved when replacing the antenna by a Jirous JRC-520 with RB433/R52n-M
Are there any known issues with the RB711 radio, or is this entirely an antenna issue?


At another customer with the same hardware lineup I got the connection up and running, although it disconnects every few hours.
Looking closer at this connection I can see that on the AP side the noise margin is listed 35ish, but on the client side it says negative noise margin, which is impossible, because then I couldnt connect to it!
The client screenshot is taken by winboxing over the client connection.
winbox_ap.jpg
winbox_client.jpg
What is the reason for these figures?? :open_mouth: Can you agree with me that the noise margin listed simply cannot be correct?

AP is running RB433 with R52n-M, client is RB711.

The diagram of this antenna does not look very impressing, with large back/side lobes:
http://www.wifihw.cz/p312-b-5g23box-b-smerova-panelova-antena-23dbi-s-integrovanym-outdoor-boxem/?page=gallery&id=1094
or am I wrong?

The antenna is also listed to range between 5240 and 5825 MHz, can operating at 5240 and thus at the edge of the frequency range cause such problems?

I would be thankful if somebody could comment on this.

2

Anyone?
:confused:

3

Your issue is simple. Those signal levels are HORRIBLE!..

4

Yes, maybe you’re right that they’re horrible, but that does not make me much wiser.

Can you please comment on my specific questions, among others:
-Why the two ends report 33 and -6 dB noise margin, respectively. They should be equal, although opposite, right? Theoretical throughput is listed as 12Mbps-ish
-Why a link is maintained although client reports negative noise margin.
I can mention that today I got feedback from the customer with this connection, praising the service and telling me everything is ok.
-Whether this antenna is crap
-Possible reasons for noise margin fluctuating 30dB on my other site as mentioned

5

Signal to noise is just that, the difference between your noise floor and your signal level. Each end of the link is going to have different noise levels depending on surrounding noise. So on the end that has the -82 signal with 33 Signal to noise your noise floor is -115 and on the other end with the -88 signal with the -6 Signal to Noise the noise floor is -82. Even if your noise level is higher than your signal you can still get and maintain a connection but you will have disconnections and a lot of retransmissions.

6

Ok, thank you.

So, based on the information available on my client antenna, do you think that the antenna accounts for the problems? I am especially concerned about the huge side- and backlobes, that might pick up way more noise than neccessesary?

7

A better antenna may help a bit but I don’t think it is going to make that much of a difference.