Importance of PIM in LTE

As the number of WISP LTE deployments increase, there are many things WISPs will need to be mindful of.  One such item is properly supporting antenna cables. LTE systems are more sensitive to cable issues.  In a previous blog post, I talked about pim and low-pim cables.   One of the things that can cause low pim is improperly mated cables.  If cables are not supported they can become loose over time.  Vibration from equipment or even the wind can loosen connections.

How do we support cables?
We can take a cue from the cellular industry. The following are some examples of proper cable support.  Thanks to Joshua Powell for these pics.

Where can you get these?
A good place to start are sites like sitepro1 or Tessco has a selection.

So the next time you are planning your LTE deployment think about cable support.

Importance of PIM in WISP LTE deployments

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”.

Google Nest – The Fast Mesh Router for Smart Homes

Google Nest WiFi is an advanced home WiFi system that can replace your traditional WiFi to provide fast coverage all over the house. It contains speakers that work with Google Assistant so that you can play music and can control the settings.

The best thing about this router is that it’s fast and reliable as compared to other Google’s products. Whether you want to connect a single device or multiple, this router will work the same for you. No matter how many devices are connected, the advanced features will help you to get fast signals.

No doubt, this time, the design is more attractive, and the company had made sure to bring Google WiFi and Google home in a single product.

Let’s discuss the detail features of Google Nest WiFi so you can understand better.

Google Nest Wifi Setup

Google Nest WiFi interface is easy-to-manage and straightforward. You can place the device in open areas as it contains parental control features. In case if you already own a mesh network product, then it would be easy for you to set the modem.

Besides, you can also set screen time for your kids, so that they don’t overuse it. Here are some simple steps that you can follow to set up this device.

  • First, download the Google Home App and then choose the location of your network.
  • Now connect the Ethernet cable with the router to start the process.
  • On the app, you will be asked to scan the QR code.
  • Once you are done with the QR code, give your WiFi a name, password and enjoy the service.

Google Nest WiFi Design

This time the design is more simple and elegant. If you are someone who is fond of simple models, then this device is perfect for you. On the router, you can find an LED light that indicates that your connection is active now.

Furthermore, on the bottom, you’ll see Ethernet ports, such as one Wan and one LAN. Undoubtedly, it’s the ideal choice for users who want to have decent routers in their houses.

In addition, you’ll see two main features on the device, one is a music play feature, and the other one is the time display. On the time display, you can set the time of the WiFi connection to manage your kid’s activities.

It helps to prioritize traffic to make your experience better when you are streaming 4k videos or playing online games. Also, the quick voice command helps you to control the live connections so that you can manage them later.

Google Nest WiFi Performance

As compared to Google’s other products, Nest WiFi performs much better when it comes to speed. You can connect multiple devices at the same time without facing any connection issues.

Furthermore, if you want to download tons of data, then this device can help you to do it in a few minutes. The downloading speed of Nest WiFi is much better than other devices, which is why it can be your best choice if you want to download numerous data in less time.

Thresholds for Microwave backhauls in Librenms

If you are running Librenms this video will help you learn how to adjust the thresholds for signal strength when it comes to microwave/licensed backhauls.  This video focuses on Mimosa because that was the quickest handy thing.  Cambium and other manufacturers will be slightly different due to chains being combined and other things.

What is VoLTE?

Voice over LTE (VoLTE) allows both Data and voice calls at the same time.  It is also known as “HD Calling” .

Lots of good info here.

The advantages
-Simultaneous Voice and Data Calls
-High definition (HD) voice calling

Sprint currently supports VoLTE.  Airspan is supporting VoLTE.

Phones which support VoLTE