Beefy grounding on a Cellular site
Beefy grounding on a Cellular site
As Internet traffic grows and becomes more dynamic, optical transport networks for sub-sea, terrestrial long haul and metro need more capacity. The ability to deploy capacity quickly is equally important to handle the increasingly dynamic nature of the traffic. The concept of a multi-haul transport platform, as introduced by Andrew Schmitt of Cignal AI, becomes very appealing for achieving this ability to scale with speed while maintaining operational simplicity – a single platform for all requirements. A critical element of the multi-haul optical platform is the flexibility of the coherent optics to be tuned to fine granularity in order to meet the reach-capacity target of any given network.
From Wikipedia https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding
virtual routing and forwarding (VRF) is a technology that allows multiple instances of a routing table to co-exist within the same router at the same time. One or more logical or physical interfaces may have a VRF and these VRFs do not share routes therefore the packets are only forwarded between interfaces on the same VRF
As some of you reading this dive into metro ethernet you should know some terminology
• User-Network Interface (UNI): The UNI is a physical Ethernet port on the service provider side of the network along with a predefined set of parameters to provide data, control and management traffic exchange with the end-customer CPE device. The customer CPE device can be a Layer 2 Ethernet switch, Layer 3 routing node or some of LTE nodes.
• Network-to-Network Interface (NNI): NNI is represented by the physical Ethernet port on the service provider access node that is used to interconnect two Ethernet MANs of two different service providers. We are also using E-NNI as a reference point for the interconnection of Layer 2 MAN service with Layer 3 service nodes—the provider edge router (PE), a broadband network gateway (BNG), vertical handover (VHO), etc—in the provider network.
• Ethernet Virtual Connection (EVC) is the architecture construct that supports the association of UNI reference points for the purpose of delivering an Ethernet flow between subscriber sites across the MAN.
PIM sweeps are a common thing in the Cellular field. One of the first questions folks often ask is what is a PIM sweep? If you think of PIM testing as a passive test and line sweeping as an active test that is a good start. PIM testing looks for problems with things like connectors, cables, and other “layer 1” items. A PIM test is not a line sweep. Line sweeping measures the signal losses and reflections of the transmission system. this is typically VSWR. A line sweep is an active test. It can not detect the same things a PIM test can. Many HAM radio folks are familiar with a line sweep where the reflected power is measure in an antenna system. In a line sweep you deal with reflected power and all that.
What does a PIM test do?
When you do a PIM test typical two high power signals are injected into the antenna line. You can actually pass a sweep test but not a PIM test.
I won’t go into PIM tests very much because you need high dollar units such as those from Anritsu and Kaelus. These cost 10’s of thousands of dollars new. Sometimes you can find these used. However, the next thing you will run into is understanding the output of such a device. Cell crews go to week long certification classes to become a PIM certified tech from Anritsu and others.
What causes a PIM test to fail?
According to Kaelus the most common problems are:
• Contaminated surfaces or contacts due to dirt, dust, moisture or oxidation.
• Loose mechanical junctions due to inadequate torque, poor alignment or poorly prepared contact surfaces.
• Loose mechanical junctions caused transportation shock or vibration .
• Metal flakes or shavings inside RF connections.
• Poorly prepared RF connections
•Trapped dielectric materials (adhesives, foam, etc.)
•Cracks or distortions at the end of the outer conductor of coaxial cables caused by over tightening the back nut during installation.
• Solid inner conductors distorted in the preparation process causing these to be out of round or tapered over the mating length.
• Hollow inner conductors excessively enlarged or made oval during the preparation process.
Why does cable matter?
Cables do not typically cause PIM, but poorly terminated or damaged cables can and do cause problems.
Cables with Seams can cause issues. The seam can corrode. Plated copper, found in cheaper cables, can break away from the aluminum core. This actually allows small amounts of flaking to happen between the connector and the core of the cable. This will cause PIM issues and is very hard to diagnose. Imagine little flakes inside a connector. You don’t see them until you break open the connector, and even then they may be pretty little flakes.
Cables can change their physical configuration as temperature varies. For instance, sunshine can warm cables, changing their electrical length. A cable that happens to be the right length to cancel out PIM when cool may show strong PIM after changing its length on a warm day, or, it can work the other way around, good when hot and bad when cold. In addition, the physical change in length can make a formerly good connection into a poor one, also generating PIM. Other environmental factors such as water in the connector or cable can be an issue, as with any RF setup.
I think I have PIM issues. What are some indications?
PIM often shows up as poor statistics from the affected antenna. One of the first and most direct indications of PIM can be seen in cells with two receive paths. If the noise floor is not equal between the two paths, the cause is likely PIM generated inside the noisy receive path.
How Do I prevent PIM issues?
Cable quality and connector quality are one of the biggest factors in the PIM quality of a LTE system. Many WISPs are used to making their own LMR cables and putting on their own connectors. There is a difference between a low PIM LMR-400 cable and normal LMR-400. Same for connectors. One of the recommendations today was to use 1/2” superflex heliax.
The easy recommendation is to buy pre-made cables that have already been PIM certified. In a typical WISP setup, you do not have lots and lot of components in your setup. Buy already certified components from your distributors that are “Low PIM rated”.
If you are looking for a U.S. stocking distributor of ALG products check out ISP Supplies
The following are results from a series of tests of AGLcom’s parabolic dish antennas on an existing link that is 5.7 miles long. The link typically passes 80-90Mbs with a TX capacity of 140 Mbs and radios used are Ubiquiti AF5X operating at 5218 Mhz. A full PDF with better Readability can be downloaded here..
The tests were taken in stages:
The tables below do not follow the test order as the third line of data was actually the last test performed.
A-Jirous JRC-29EX MIMO
B-Jirous JRC-29EX MIMO C-AGLcom – PS-6100-30-06-DP D-AGLcom – PS-6100-29-06-DP-UHP
Table 1 is the signal strength results of the various dishes on the link. The first line, A-B, is the original Jirous to Jirous. A is the first two columns of the link and are the A side and the last two columns are the B side on the link. What is of interest is that exchanging B to C in the second line brought the signal deviation between the channels to only 1db and 0 db as seen in Table 2. The third line was a result of replacing the horn on the A dish and optimizing the setting on the AF5X radios. This changed the signal by around 7db and improved the link capacity, Table 3. Clearly, the A dish had a problem with the original horn.
In the fourth line, D-B, the signal strength improved as well at the signal deviation on the two channels, Table 2 first two columns. This link was not optimized. The fifth line, D-C is both AGLcom dishes which improved the bandwidth, Table 3, and the signal deviations, Table 2. The final line, D-C, was the previous line optimized. The signal strengths moved closer together and the bandwidth improved.
Link Ch0 Ch1 Ch0 Ch1
A*-C -64 -66
D*-C -60 -60
-70 -74 -71 -71 -65 -66 -59 -59 -58 -58 -61 -61
Signal Strength (* optimized data) Table 1
Table 2 has four data columns, the first two being the measured results and the latter two being the measured difference from theory. The Jirous and AF5X calculators were used for the theory signals. Clearly the signal approached the theoritical limit with the optimization and with the change of dishes. The optimization improved the signal by ~9db for the link that we replaced the horn on the Jirous and by ~2db for the AGLcom link.
Link dSig dSig A-B 3 4 A-C 1 0 A*-C 2 1 D-B -1 0 D-C 0 0 D*-C 0 0
dSig dSig -16.5 -17.4 -17.0 -15.0 -8.0 -9.0 -13.3 -5.3 -7.0 -4.3 -5.0 -6.0
Signal strength variation from theory Table 2
The band width improvement was more obvious, Table 3, from 22 Mbs to 39 Mbs for the RX and 144 Mbs to 141 Mbs TX for the link with the horn replacement. The bandwidth improvement for the optimization of the AGLcom link was from 61Mbs to 66Mbs RX and from 211Mbs to 267Mbs for TX.
The bandwidth improvement from the original, optimized link to the AGLcom link is from 61Mbs RX to 67Mbs and from 210Mbs TX to 267Mbs. There is a clear improvement for the AGLcom link over the Jirous link.
BW-TX 144.6 141.4 210.0 211.0 215.0 267.6
The data supports a measurable improvement in both signal strength and bandwidth with the use of the AGLcom dishes. However, it is difficult to quantify the improvement. The Jirous dishes were identical whereas the AGLcom dishes were not. One of the jirous dishes was under performing initially but was repaired for the last tests. Additional testing is needed to provide accurate data analysis and performance comparison. The best performance tests would involve identical AGLcom dishes, ideally two links, one each of both types of dishes.
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Below is a 5-minute average over a half hour or so.