Intermittent Backhaul Issue (5.7), Very strange!!!

I am having a very strange problem with a set of 5700BH’s. I have a 27 mile link, both sides have Reflector Dishes, the slave side is on an FM Radio tower, at approximately 250 ft., and the Master side is on a grain elevator at approx. 160 ft.

I originally was using 2.4 GHz Canopy backhaul units on dishes, and the link was solid orignally. Then after maybe a few weeks, the link started going up and down spuratically. After viewing the spectrum analyzer on each side of the link, it seemed like I was getting interference. So, I replaced the 2.4 units with 5.7 GHz backhauls. The link came up instantly with good signal (RSSI: ~1000, -76 dBm, Jitter: 3-4). I thought the problem was fixed.

Then, after a couple of days, the same thing started happening with my new 5.7 GHz units. The link will be up with good signal, and then all of a sudden the link will start going up and down, registering and re-registering. When this happens, my signal levels go in the tank (RSSI ~750, -85 to -90 dBm, Jitter: 7-15). When I look at the spectrum analyzer, there is nothing that looks like interference or anything on the channel I am using, only the signal being put out from the Master. I have checked the spec. analyzer from both sides (had to change the Master to a Slave, obviously) and everything looks fine.

I get paged by What’s Up Gold when this thing goes down, and for whatever reason, it seems to start going down in the evening around anywhere from 6-10 p.m., be inconsistent and spurattic all night, and finally come back up solid around 9-10 a.m. This happens maybe 3-4 nights a week, and sometimes it will happen for a short period during the day. Sometimes it will run for 3-4 days with no problem at all. My BH Master is being timed, and GPS always has a 3D Fix. My Ethernet connection to both sides is always up.

I checked, and double-checked Fresnel Zone clearance, and i am fine there (this link is in western KS, nothing but flat grain fields :smiley: ). The only thing I can think of is that i am not getting enough DC power to one of the two radios. As in, it has enough power to be booted up and have an ethernet link, but not enough power to run the radio effeciently. I have not checked my Voltage/Wattage at the end of each cable. Does anyone know the minimum amount of power that a Canopy needs to run correctly? On the FM Radio tower side, my cable is around 300 feet, but is within the standard 328 ft. “guideline”. I have heard stories of people using PoE equipment that acted quirky if not enough Voltage/Wattage was getting passed through the cable. I have not tried replacing the Ethernet at either end, so I could possibly have a questionable cable.

Any information/thoughts that anyone can give me would be greatly appreciated!!!

300 feet is close enough to 328 feet. Is this shielded cable? Is the cable in any type of conduit? I would definitely suspect the length of the cable and the environment. The cable could be realizing interference from other transmitters at the site.

The cable is not shielded, and not in a conduit. On the same tower, i have a Canopy 2.4 GHz AP at close to the same height, that has non-shielded cable, not in a conduit, that runs fine. Both of these Ethernet cables are coming down the same leg of the tower. Do you think that maybe the cable in question has something wrong with it (kink, tear, etc.) that could be causing the issue I am seeing?

Yes, its definitely a possibility. It is highly recommended that you use shielded cable in an RF environment such as on a tower.

Does the 5.7 link seem to drop in signal strength at or around the same time of the day as the 2.4 did in the past? How close are your Canopy units to other antennas on the tower?

Yah, the problem does seem creep around the same time as the old 2.4 BH. The only antenna that is close to this backhaul on the FM tower side is our 2.4 AP. Probably about 30 ft. away.

On the grain elevator side, I have another Canopy 5.7 BH that is timed off of the same GPS unit as the BH in question, and it is always up and running. There are a few other antennas on the elevator (mix of 5.8 and 2.4) that are always up and running as well. And like I said earlier, I don’t see any interference on the spectrum analyzers…

Are all your devices on the elevator Canopy units? If so, are they all either BH Masters and AP’s? Are they being timed with a CMM or CMM Micro? If they are all BH Masters and AP’s, are their downlink data percentage parameters set to the same value? What type of vertical seperation do you have between all these devices?

Altogether, there are 2 Canopy 5700BH’s, both masters, plugged into an after market Timing/GPS Unit (FDDI MiniGPS 2). Those are the only Canopy’s up there. One points East, and the one in question points South. The South pointing one is about 6 feet higher than the East facing one.

There is a 5.8 GHz Breezenet DS.11 backhaul pointing West that is about the same height as my south facing backhaul. There is a Breezenet 2.4 GHz Pro.11 AP on an Omni antenna, and a 2.4 GHz Orinoco AP-1000 AP on a sector antenna pointing SouthEast. All the 2.4 equipment is about the same height as my South facing Canopy BH and the Breezenet 5.8 DS.11 BH. The 2.4 stuff is amped, none of the 5 GHz stuff is.

The downlink data % on my Canopy BH pointing East is set to 50%, and the downlink data % on my Canopy BH pointing South is set to 30%. Do they both need to be the same?

I would try and change them both to 50% and see if it makes a difference. If the timing device is working properly, they should both transmit at the same time, but the value in the downlink data percentage param has an effect on the length of time the unit will Tx and Rx I believe.

In a full AP-cluster, Motorola recommends that all AP’s have identical downlink data percentages, and the same goes for co-located backhauls in the same frequency band.

You sure do have a lot of transmitters on this elevator. I drew it out, and the 5.8 backhaul facing west at the same height level as your Canopy backhaul facing south could cause a problem.

What are the exact frequencies that you are running? If your timing device is doing its job, I don’t think there is self interference between your Canopy Backhauls. Two devices (AP’s or BHM’s) that are 180 degrees opposite of each other should be able to run on the same frequency without problems. I have stretched this rule a bit with BHM’s, with plenty of vertical seperation between the two.

Although you said your spectrum analyzer reports that there is no interference, I would start turning off some devices at the elevator-site one at a time and see if this problem goes away. Can you think of any type of peak usage that is occurring on your network during the times that your link goes down?

Are you running 10 or 20 meg bh’s?

I am having the same trouble with my 20 mile link, I have a 4’ dish on the slave side and a reflector on the master side an Rssi 1200 Jitter 1 and power level of 55, My trouble is also at night, but not every night. I can change to 10 meg and the link will stay up. I’m going to put the P9 version so it will switch when the power level starts to rise.

I have also talked with a couple of others that are having the same trouble.

When links get that far the 20 Meg BH’s have trouble. I believe I have read that the newest firmware version has a feature in it that will throttle the modulation back to 10 Megs if the link becomes marginal when set to 20.

When installing and pointing BH-20’s, we always initially configured them for 10 Meg modulation. Once the link was established, we switched over the 20. We did notice a few db of loss once the units were switched to 20 meg modulation, but they are still stable. I think the farthest shot we have done with 20 Megs is around 7 miles.

we have done a similar thing, 18miles but running at 10M

I don’t have any trouble running at 20meg 99.1 percent of the time, it’s just when the power fades I need to switch back to 10meg to keep it up at 100%

Radio and TV stations are allowed to up the power in the evening.

Try a 4’ Big Boy satellite dish on one end. That will give you some more margin.

Also as previously mentioned I would suggest shielded cable. Ground the shield to earth at the CMM side and float it at the radio side. This way the noise will be shunted to ground.

I have had mixed experience with FM, got 2 clusters colocating on FM no problems,

Over weekend needed to remote SM/AP on a FM tower and major headaches, ground level everything is ok, attach equipement to the base and all is good, climb 40 feet and place it next to the tower leg, and can’t ping the units anymore, clime 5ft higher and all is good, another 5 and can’t ping again (this is directly connected over ethernet).

Cable was not shielded, in the end put up a secondary 20ft pole 30ft away and everything is working fine ?

Where can you get these 4ft dishes. Also any one with any expreince of shooting over water need two links the first 27 miles over water and the second 50 miles ?

Commercial DSS Dishes will work, you will need the mount that comes with the new Canopy 27" dishes.

a 50mile link you say? I have never shot that far.

eagle-tech, did you ever resolve this problem?

I do have a 4’ dish on one side it helped the power level we went from 73 to 55 but it still drops out. only once this week.