Backhauls not registered properly

Hello all,

I’m having a weird problem. One of our link which is linked by two 10 Mbps backhauls is registered for a while and after sometime goes off and again it gets registered after a while. I don’t know what exactly is the problem because the reflectors are fixed and the link is registered at -76dbm with jitter as 2/3. Can there be any problem with the backhauls at any of the end?

Can anybody please help me out on this?
Any suggestions is extremely valuable.

How long is that link?

Make both units slaves and then do an RF spectrum analysis on both. Observe the noise level at the frequency you are on.

Are either of the BH’s on a tower with AP’s in the same frequency band?

Thank you guys.

First of all the link is just 29.68 miles. I guess the distance is not the actual matter here…

and about the interference the backhauls are in extreme remote locations where there is hardly any equipments.
But i’ll try the frequency checking my making both as slaves.

Thank you again for your quick response.

Out of Topic Question:

How far are you from foot of Everest?

just about a hundred miles away from the foot of the everest.

can i know why have you quoted as out of topic question??

Because you are telling about your BH problem, and when I see your location, I courageously asked. But I labeled it as OUt of Topic so that you might not be offended when you see it, while you are having problem, i am interested in asking your place instead.

It could be one of the following

1. Misalignment of the backhauls due to movement of wind.
2. -76 dB is not good enough for such long links
3. There could be ducting, hot air cold air causing refraction of waves

just my two cents

-76 it’s not good enough. When weather goes a little rainy your signal drops and you loose the link. Try making it something like -70 dBm. Use the lowest channel if it’s free form interference.

If you have pictures from snowy mountain tops and Canopy please share them with us.

I usually got 59-60db on my 14mile link.

Thanks to all of you for your help.

As you people have said that -76 is not good for such long link but its the best we had after aligning the reflectors at both ends. I’m using the frequency in lower 5.8 GHz range.

Can i ask you guys that which reflectors do you use generally in this type of long link?

Any suggestions in regards to the reflectors i should use???
and sorry erkan i don’t have the pictures of snowy mountain but i’ll try to share what i have.

Thanking you again.

are you using the 27RD? or the Wireless Beehive Reflector?

A path analysis based on your mileage, transmitter output of 23dB (200mW), 18dB antennas…

I found you should see -83dB at the receiver… Hmmm… Either the path calc is flubbed or something else is messy.

-85dB is the sensitivity of the receiver in 2-level modulation, -79dB is 4-level modulation.

As such…

You are running 2-level when you use 10Mbps PTP radios… You need to get something like 20dB of fade margin in your link. You have 200W EIRP to play with in the 5.7/5.8GHz band.

I’d suggest getting your backhauls connectorized and putting different antennas on.

I’d suggest a minimum of 28dB of gain on the antenna… Most 2-foot solid dishes will have that. You could increase fade margin and go to 30dB of gain, which gives you around another 4dB. You could bump it to 31dB of antenna gain and have 26.48dB of fade, and 198dB EIRP.

This’d be damn good. You can use higher gain antennas, but you’ll need to adjust the transmitter output accordingly. You can get around 37.9dB of gain from a 6-foot dish.

These guys have what you need. … h=22_50_48

More power Jerry!

Always ready to give a helping hand.

AMD phreak,

The canopy 27 RD gives 24 dB of gain when you add 7 dB of internal antenna again. I have links at 74 km using 27 RD and the signal I get is -71 dB.

I have links running fine for 3 year that are over 40 km and are on 27 RD with -66 dB. They have never lost sync even during severe storm and rain. Though they tend to go down to as much as -83 dB, but at 10 mbps, they still pass traffic.

Now real long link, I have a 6-foot radiowave dish and connectorized canopy at one end and 27RD reflector at other end and I get -58 dB at a distance of 80 km. I run this link of 20 mbps mode and it give me more that 5 mbits of duplex throughput.

I would suggest increasing the gain of antenna but I would not suggest anything other than 27 RD at both ends if you are running 10 mbps mode and the spectrum is clean.

If you want 20 mbps mode and spectrum is not clean you would certainly need higher gain antennas.

Just curious as to why you would not suggest anything other than the 27RD on 10Mbps modulation?

Another thing I forgot to mention is that there might be a fresnel issue. I’d suggest to the OP that they run some path analysis to see if there is a fresnel issue. If there is, the link might work, but the signal strength would be lower than to be expected compared to a path without fresnel problems.

Because 27RD seem to perform very well and in 10 mbps mode you need 3 db of CNR and for links within 50 km I have had no issues with them till now.

There is no other reason apart from that but bigger is always better.


I understand the 3dB of c/n ratio, but that does not take into account fade due to environmental conditions.

I have watched a real microwave system that was not designed with enough fade margin to compensate, go tango-uniform during a really bad dust storm. Granted, we are talking different frequencies (higher frequencies) and as such there are other factors… Still though, one should try to get as much fade margin as is realistic. I have found that 10-15dB of fade is adeqate for this area in the valley, but wouldn’t trust that in the mountains here due to snow and ice buildup on antennas and radomes. Pushing it to 25dB+ is about the best.

As with everything wireless, YMMV. :wink: