Frequency does matter

Recently we installed a PTP 550 link for a client.  This is a connectorized version with 2-foot dishes on it for a four-mile link.  Overkill you say, but the idea is the dishes make up the gain and not transmitter power.  A much cleaner signal can be achieved which falls within the FCC guidelines for total EIRP.

So let’s get to it.  Our first image is out path.  This link had clear line of sight from a 150-foot foot water tower to a 240-foot tower.

Google Earth Path

The 240 Foot tower

150 Foot water tower

After getting out of the cold we let things burn in for a few days. This is what an initial spectrum analysis looked like.

Radio Frequency set on 5820 mhz

Radio Frequency set on 5200mhz

As you can see the RSSI was within 2 DB, which isn’t terrible.  However, due to interference, the MCS rates are markedly different, which is what results in the big differences in speed.  Please note this is only with one radio enabled and on a 20mhz channel.  We fully expect bigger speeds once we up channel sizes and enable the second radio.

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Supporting Cable

This will be a fairly short post. As they say, a picture is worth a thousand words. If you have wondered a good way to support your cable when you are hoisting a radio with cable on it this picture is for you. The cable could be fiber,cat-5, or a larger hardline.

Photo courtesy of Heath Schaff

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Hangers to help with PIM

Are you running Telrad or Baicells? Need a solution to get every bit you can out of the system? Don’t forget your hangers can influence pim .

Traditional hangers and diameter-specific grommet combinations complicate installations, making it difficult to secure cables from wind and vibration, which can cause passive intermodulation (PIM) problems. 

Check out PIM hangers from Tessco.

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ALG Antenna test vs Jirous dishes

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:

  1. 1)  The normal performance of the link was recorded.
  2. 2)  The 2′ dish at one end, B, was replaced with the AGLcom, C, dish and the link reestablished.The link performance was recorded.
  3. 3)  The 2′ dish at the other end, A, was replaced with the AGLcom, D, dish and the link reestablished. The link performance was recorded.
  4. 4)  The setting on the AF5xs were adjusted to optimize the link performance with data recorded.
  5. 5)  The 2′ dish, B was put back in the link and the performance was recorded.
  6. 6)  The ACLcom C was put back into place.

The tables below do not follow the test order as the third line of data was actually the last test performed.

Antennas:

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

Results:

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

  1. A-B  -73 -76
  2. A-C  -73 -74

A*-C -64 -66

  1. D-B  -63 -62
  2. D-C  -62 -62

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.

Link BW-RX

  1. A-B  22.5
  2. A-C  39.0

A*-C 60.9

  1. D-B  61.4
  2. D-C  60.6

D*-C 66.6

BW-TX 144.6 141.4 210.0 211.0 215.0 267.6

Table 3

Conclusions:

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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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.

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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.

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