Vendor Spotlight: Subcarrier Communications

Over the past several WISPA shows I have had the opportunity to chat and get to know CEO John Paleski from Subcarrier Communications (www.subcarrier.com). John is very in-tune with how the WISP industry functions in terms of tower needs.  Many of the big tower companies tack on so many fees with their towers it makes leasing a tower out of reach for many. Add on the processes in place can be a deterrent to getting equipment in place.

Subcarrier has addressed many of these hurdles for the WISP industry.  Reasonable rates for tower rent are always a concern, but if the business model is there for the WISP, they are not the primary concern many times.  Not only has subcarrier realized many WISPs are utilizing smaller equipment, but things like huge application fees are a negative for the smaller WISP. Subcarrier knows what is on their towers. Such a simple thing means a rapid and smooth deployment for the WISP.  After several conversations with JOHN, it is apparent he knows just about every tower in his inventory.  He can tell you if they will support what you are wanting to hang on that tower without running a $2000 engineering study right off the bat.  On the flip side, he isn’t compromising safety or integrity of the tower.  Many towers, such as old AT&T long lines towers were built to such high specifications if you just apply a little common sense and some quick figuring you know the typical WISP deployment isn’t going to add any significant amount of loading on the tower.

I believe that John thinks the same way many of us in this industry do.  An empty tower is not making anybody any money.  If it makes sense for both parties then a deal can be made.  Too many of the larger tower companies only look at deals that make sense for them.

I would encourage any of you looking for towerspace to check out the sites Subcarrier has.  Check out their interactive Google Search to see if they have some towers you could use. Tell them Justin sent you over.

Tower Suppliers

One of the more common questions we get asked about is towers, tower mounts, and where to get them. If you are looking to mount to Rohn towers check out our friends over at ISP supplies. They have many of the mounts you would need for Rohn 25-65 and some of the other Rohn series towers.  They will also be an exhibitor at the Upcoming WISPAMERICA in booth 700.

If you have larger towers or larger requirements check out companies such as SitePro1 or Tessco.  Both of these companies carrier mounts designed for monopoles and larger carrier style towers.

Aligning an 80GHZ link at a mile and other licensed backhauls

Recently we had a teaching moment for a couple of folks who had not had much experience with aligning higher frequency antennas with very tight beamwidths.  This particular day we were aligning 2 foot Siklu 80GHZ antennas.

One of the questions we often get asked is how do you align these? These questions are usually asked by someone who is familiar with aligning 5ghz antennas with a 10 or 20 degree beam which you can eyeball and has tried a microwave shot. They find out it is much harder.  The higher you go in frequency the tighter and smaller the beam is.  Distance also affects how far off you can be.  Think of it as a laser pointer.  If you have ever taken a laser pointer out at night and shone it a long distance you will notice even the slightest movement will cause it to jump inches, even feet.  Keep laser pointer analogy in mind for this next section.

In order to understand alignment, we need to understand lobes on an antenna. An antenna is just a device that focuses radiation in a direction.  In a licensed microwave setup, these antennas focus the radiation in a tighter “beam”.  Let’s go back to our laser pointer analogy.  Some laser pointers project a smaller dot at 10 feet than others.  Same for antennas.   The diagram below shows what is called the main lobe and the side lobe.

The way to get the best signal is to get both dishes locked on to the main lobe. Sounds easy right? With higher frequencies, you are talking about millimeter waves. This means the main lobe may only be 3mm wide, about the size of this text on a laptop screen.  Now imagine trying to keep that 3mm beam in the center of a paper plate at a mile.  On top of that, the difference between the main lobe and locking onto a side lobe could be the difference of 1-2mm. A slight wind can move a dish 2mm.

To give you a real-world example. A 2ft 23 GHz antenna having 3 dB beamwidth of 1.6 degrees. Allowing for a path length of about 2.5 miles (this is licensed 23GHZ) the actual beamwidth at the receiving antenna is around 370 ft and is, therefore, likely to be greater than the height of the tower. If the antenna’s out of horizontal by even a couple of degrees to start, the antennas will miss by around 460 ft and not be able to “see” each other. This can be amplified as frequency and distance increase.

This is all fine and dandy, but what about the practical world? How do I align the thing?
It all starts with the FCC path coordination paperwork you will receive on your licensed link. There is a wealth of information in here.  It tells you all of the following:
-Your mounting height (this is typically already known)
-Your heading (more on this in a bit)
-The antenna angle downtilt or uptilt (very important)
-The expected signal target

Armed with this information you will have all of the information you need to align the link.  From this point, the philosophical side of things kicks in.  Some tower climbers are good with using a compass to get their exact bearings.  Others have high dollar tools to do it all via GPS such as microwave path alignment from Sunsight.

What everyone doing alignment should have in their toolkit are the following:
-A small magnetic bubble Level. We want to make sure we start with a level mount.  We would be fighting an uphill battle if the pipe or standoff we are mounting to is not level.

-An angle Finder is very helpful for determining the antenna down or uptilt per the path calculation.

Obviously, the above tools are just one of many examples.  There are more expensive ones and bare bones ones.  Tools are only as good as the person using them.

-Ratcheting wrenches for the left and right and up and down adjustments.
Having ratcheting wrenches makes fine-tuning a very easy process.  You will see why later.

-A good hands-free communication method.  Depending on the tower FM communications may or may not work.  Cell phones may or may not work. Being able to talk to the crew on the other end is crucial.  And yes, to make this smooth you want a crew on the other end.

Aligning backhauls, especially microwave, is a skilled trade.  With any skilled trade, you will get all kinds of tips and tricks of the trade.  Some you may use, others you may not.  Ask any Carpenter, Drywaller, or Mason and they will tell you little tips and tricks. They probably all are great and will work, but you may only use some of them.  I am going to tell you mine. You may find others you like better.

We always start with a google earth plot of the path. I call this Phase 1.  The goal of phase 1 is to get the radios talking.  We make sure the line is exactly on the two points, not just approximate.  If the backhaul it on the left side of the tower, we draw the line to/from the left side of the tower.  We then pick 2-3 landmarks along the path as we can.  We start with something close to the tower the climber should be able to see.

In our photo above we have picked out two reference points close to the tower the climber can see.  The first is the clump of trees on the climbers left.  The path passes “just to the right” of the edge of the end of the trees.  The second reference is the intersection of the county roads about 2-3 miles out.  Our path should be just to the right of those.  That point of reference is more of a sanity check. More than anything. The climber at the other end has a similar printout.   I have found communication during this process works best if both climbers and someone logged to at least one radio on the ground with a laptop are on a conference bridge.  Many radios have lights, tones, or multimeter outputs to indicate signal.  Some modern radios only have web-interfaces and apps.  Hold a phone while trying to align can be cumbersome.  This is where the guy on the ground can take some load off what the climbers are doing.

Regardless of the mechanics of the radio, the goal of Phase 1 is to establish a radio link, no matter how bad it is. Now, here is where the real meat and potatoes of backhaul alignment come into play.  This is a very deliberate and calculated process.  Your goal at the end of the entire alignment process is to end up with the following diagram

What many folks don’t realize is it is possible to establish a signal on a side lobe. So how do you know if you are on a side lobe? Here is how we start phase 2. This is what I call fine-tuning. Real original huh? Depending on good, or lucky you were during phase 1 you may have a long way to go or a short way to go to meet target.  Remember that in your paperwork we talked about earlier?  One side and one side only starts moving their fine adjustment on their antenna to the left and right and up and down.  This is typically called sweeping.  The key thing to note here is you need to find the very edges of the radio signal, not just the lobe you happen to be on.

Let’s take a real-world example to explain how sweeping affects main and side lobes.  At the start of this article, we mentioned an 80ghz link.  With our phase 1 rough alignment, we were able to get linked at a -86.  The target was a -32.   The first side to start alignment started sweeping to the right, signal started going from a -86 down to a -72 rather quickly. This was using very small turns of the adjustment.  The ratcheting wrench was only clicking 1-2 times for each 2-3 db of signal change. Once it reached a -72 it started climbing back up.   The climber then kept going to the right to find the edge of the signal, not just the lobe we were on.  The signal started getting worse until we were back into the upper 80’s.

Now, the climber brings the alignment back to the left, and stops at the -72 and makes a mental note of where that is in relationship to the overall placement of the dish, etc.  Some mounts have distinct notches, some guys use markers, others just remember.  Now the climber continues on to the left and the -72 gets worse and goes back down to the -86 and continues to get worse.  So the climber, at least for now, has found the sweet spot for the left and right alignment.  The climber also knows this will probably change, but has found it for now.   Climber repeats the same procedure for the up and down. Due to the anglefinder, the climbers have with them they feel pretty confident they are fairly close with the up and down so they do not adjust the up and down travel as much as the procedure goes on.

Next, the other side does the same procedure the first side did. They do the left to right and get the signal down to a -62. Essentially, what the climbers are trying to do is find the center, which will contain the strongest signal, by sweeping past the other signals.  Keep in mind there may be only millimeters separating these other lobes.  Due to physics, and the shape of the signal, the first lobe is actually stronger than the edges of the main beam.

Say what? The first lobe is stronger than the edges of the main beam? Yes, but not stronger than the main beam.  Let’s go back to our installers. They have each had a go around at alignment and are only at a -62.  On a 5ghz backhaul that would be respectable, depending on your noise floor. But we are 30db away from our target of -32. Some climbers, incorrectly I might add, try to do a shortcut by scanning in an x pattern instead of x and y-axis separately. This makes it easier to lock onto a side lobe.

80ghz backhaul

So now our first climber goes back to making the left and right adjustments.   At this point, the installer finds something odd.  He has gotten the signal down to a -55, but that’s the best he can do. Even a small turn jumps the signal up    Then our installer remembers the above statement.  The first lobe is always stronger than the edges of the main beam.  He gets the signal back down to a -55 and turns the alignment over to the other side.

Here is a very important thing to note.  Both of our installers have now “gotten a feel” for the few turns needed to adjust the signal on these dishes.  To them compared to 5ghz dishes, these are very tiny and almost insignificant movements. But they sure make a difference in signal.  Now our installer at tower B has his second alignment session.  As he is making adjustments the signal is not changing.  He is moving his wrench for what seems like forever and the signal is barely moving, Any other time their signal would have been a -90 or dropped.  What has happened here? The main lobe of one side has locked onto the first lobe because it is always stronger.  Since the main lobe is bigger it seems like it takes forever to make any change.  If we had a guy on the laptop he was probably also probably seeing very mismatched data rates.  One side was probably much higher than the other by a large margin.

Then boom, all of a sudden the signal goes from a -55 to a -42.  A 17 db jump!   We can now tell we are on the main lobe.  If the laptop person looks at the data rates now they should be more balanced.

Data Rates on a Mimosa B11 Rates properly aligned but not fine-tuned

At this point, it is just a simple matter of each side making finer and finer adjustments back and forth to get the signal down.  If you think of the above circle/crosshair you are making smaller and smaller adjustments to nudge toward the center of the circle. This is where the ratcheting wrenches help by giving a very measured amount of travel.  This helps with the whole feel of alignment.  Much of it is feel to see how much you can move the adjustment mechanisms to make the numbers move.  Sometimes it may be a single click of the wrench.  Sometimes it may be one or two.  It just depends.  As you get closer and closer to target you are moving the adjustment less and less.

As you get closer and closer to target you need to be thinking about how tightening down the adjustment bolts will affect the alignment.  Even tightening them down snug can affect the signal.  That extra amount movement to tighten them down can move them slightly past their alignment center.  You may need to take into account the amount of travel it takes to tighten down the adjustment bolt into account on smaller dishes.  If it takes a half turn of the bolt to get it tight you may need to stop a half turn and tighten “into” target.  As you tighten it down fully that is where you end up in align.  If you wait until you are in align and then snug it completely down, the force of snugging it down may pull it past and you will end up with a worse signal.

This article sprinkled in some examples from a real-world install, with some theory, with some practical knowledge. Your mileage and experience will vary.  Your experience with 6ghz vs 80ghz will vary as well. Each frequency will have it’s own quirks and tricks.

Tower crew in today’s world

One of the questions we often are asked is why our rates for tower work are what they are. In today’s world, a tower crew needs the following, not only for themselves but to protect and do the best job for the client.

The first key is equipment.  Having a crew with proper ropes, proper lifting blocks, and pulleys, and proper safety gear goes a long way. A job can be done more efficiently with the proper tools.  In-Shape tools make a big difference. How many times have you gone to cut something with a dull blade? Tools get used up and have to be replaced.

Next up is safety and insurance.  I lump these into the same category because an insured crew is safe for the client.  Having the proper insurance protects the client from anything that may happen.  Tower work is dangerous work.  With insurance requirements comes updated training. Not only does this teach crews new methods of doing things, it helps them in becoming complacent in safety practices.

Availability is the next thing. Having a crew that can roll out in a timely manner to meet client’s needs takes a dedicated staff.  We see too many part-time crews not bringing in enough money so they are having to moonlight doing other things this lessens the availability because you have to find steady work to have quality people.

The last thing is the experience our crews have.  Having been a veteran of the WISP industry for over 12 years I have seen many ways of doing things, so Have the rest of the experienced folks in our crews. We have done night climbs, harsh weather work, and custom work.  Having someone who knows the WISP industry doing your tower work makes a huge difference.

Tower Climber Harnesses

Recently there has been a thread on WISP-Talk about the best tower harness. Rather than going down the road of the best brand I figured I would take a different approach.  I sat down with Lee and Nick from TowerOne Inc. at WISPAPALOOZA 2017 in Las Vegas.

I asked them what they look for in a good harness and here were their top features.

Both said weight was very important.  This makes sense because you will be spending long amounts of time with the harness attached to you. Another feature was the ability to customize the fit.  Belts with synch type adjustments tend to be more comfortable than belt buckles with holes every 1 inch.

Attachment and gear hooks came in next as a must-have feature. Breathability of the material was another one.  After a hot day on the tower, the ability to whisk away as much sweat as possible is vital to be as comfortable as you can.

TowerOne usually brings several different types of harnesses with them to their training events.  This way folks can try things on.  One that has been discovered is people tend to make how the harness is put on an important decision when buying a harness. Some like to put their harness on like a vest.  Others like stepping into the harness and then pulling it up.

So no matter what harness you go with, look into what feature are important to you and how it feels.

Antenna Interference issues

Recently, we had a client question why we didn’t mount antennas higher up on a tower with an FM repeater on it. The top of the tower has an FM repeater on it so we mounted the equipment about 25 feet below that.

When you are talking about antennas and transmitters the basic thing to remember is it’s all radiation.   Good antennas have predictable drop off patterns and, when paired with a good transmitter, have crisp frequency drop offs.  However, there is still radiation emitting from feedline and the antenna on the tower. Many FM repeaters use a dipole design.  Some are folded, others are different types.  Below is an antenna pattern from a Dipole antenna.

As you can see there are a few patterns radiating from the antenna.  These patterns should be taken into consideration when mounting your equipment near FM, UHF, or VHF systems. Radiation may interfere with things such as your cat-5, or your PIM.  In an earlier article, I talk about low-pim cables and what affects PIM.  This is very important when you are deploying LTE gear.  RF radiation from high power transmitters can cause PIM issues if the wavelength happens to coincide with the wavelength of the other transmitter.  This does not mean they are on the same frequency.  Remember, in RF you have full wave, 3/4,1/2, and 1/4 wavelengths to deal with.

Other things to consider are near and far field patterns.  If you want some heavy reading you can read about it on Wikipedia.

Our next issue and the most common issue is the radiation getting into our Ethernet cables as well as our radios on the tower.  Below illustrates the propagation of signals coming out of an antenna on the top of the tower.  If you notice, some of the radiation is directed underneath of the antenna. Any equipment mounted too close underneath will be bombarded with radiation.

Too much radiation can cause link negotiation issues,  signal degradation,  and other issues.  By moving our antennas out of the patterns of other antennas we can make for a more reliable system.  This is one case where higher on the tower is not always better. Just because another antenna is not mounted in front of another it does not mean they are in each other’s radiated patterns.

DOL-OSHA and FCC release Communications tower best practices

The Occupational Safety and Health Administration and the Federal Communications Commission are concerned about the risks faced by employees in the communication tower industry. Employees climb communication towers to perform construction and maintenance activities and face numerous hazards, including fall hazards, hazards associated with structural collapses and improper rigging and hoisting practices, and “struck-by” hazards.

You can read the safety document here.

 

The Importance of cable support in LTE deployments

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.

WISP LTE, PIM testing, and quality

One of the topics that came up during the Baicells troubleshooting tips was the notion of PIM testing, and cables which are PIM rated.

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”.

WISPS growing up in the tower industry Part 1

As more and more Wireless ISPs (WISPS) get into licensed microwaves, bigger antennas, and fiber up the tower (FUTT) they are getting into an arena typically reserved just for the Cellular and broadcast folks.  This can result in an overwhelming amount of things to deal with.

If you are renting space on a commercial tower managed by a regional or national company such as American Tower (ATC) you will run into things like application fees, engineering studies, and closeout documents to just name a few. Once you have your notice to proceed (NTP), the real work begins.

During your negotiation phase, and in your contract, you should have a center line on the tower.  This states the center line on the tower where your equipment is mounted.  An example is if your centerline states 200, on most contracts that means you have something like 5 feet above that and 5 feet below that.  Think of it as a window.  You have a window of 195-205′ on the tower for your equipment to fit in.

IMG_9712

Centerline example. Photo courtesy of Michael Pelsor

The equipment you put on the tower was specified in the engineering phase of the paperwork.  Model numbers of mounts, antenna models, and all that are decided before the first piece of equipment is ever put on the tower. This is very important to adhere to because many tower companies will require a closeout procedure.  This normally includes pictures of your equipment and how it’s mounted, pictures of what is called a tape drop, and other things.

IMG_4586

Tape Drop Pic courtesy of Michael Pelsor

The sheer amount of things to think about on a commercial tower with multiple tenants could extend this blog post on for a long time. But, one of the biggest things to consider is when you are installing how your cable runs, antennas, etc. are in relationship to other equipment.  Are your cables somewhere they might be stepped on by someone passing your equipment to get to theirs? Does your equipment cross mounts which may be removed later or modified?

In the second part of this series we will talk about some of the higher-end tools which may save you tons of time, thus paying for themselves rather quickly.