Short Point-to-Point Upgrade

Short Point-to-Point Upgrade

I recently had the opportunity to upgrade an old point-to-point link for a concrete company. The link distance is about 300 feet, or 92 meters. They had an old Engenius access point installed very poorly on the outside of their office, about 7 feet above the ground. The network cable was taped along the floor and out a window, which was then closed on it, pinching it quite badly. The business owner was complaining of slow speed and frequent disconnects.

Old access point

The client device was a Hawking HW2R1 (product page) “smart repeater”.

Old batch plant smart repeater

Old batch plant smart repeater

This device was inside the batch plant, which is a solid concrete structure with tin siding. Attenuation much? And yes, the antennas were like that when I found it. The middle antenna is for the uplink to the AP, and the two side antennas are for client connections. I wasn’t able to log in to the device to check on its RSSI levels or configuration. I could have checked the signal levels in the plant with WiFi Explorer or Chanalyzer, but I think it’s pretty obvious why the link wasn’t working. Besides the client being inside the plant, a few problems with the AP install could have been causing issues:

  • network cabling being pinched and kinked by two doors and a window,
  • access point hanging from the antenna by the RF cable, and
  • trucks driving or parking in front of the access point.

A quick run-through with Ubiquiti’s AirLink planning tool gave me a link budget and a target received signal level for installation. I wasn’t doubting that the link was feasible; you should always have an RSL number to aim for when aligning a point-to-point link. You can see from the image that the expected level was about -48 dBm. I always try to get within 2 dB. Alignment can test your patience when using very directional antennas with gain upward of 40 dBi and beamwidths of less than 2 degrees. I once spent an hour fine-tuning an 11 GHz dish with a beamwidth of 1.4 degrees.

crc airlink

Ubiquiti’s AirLink tool

I installed two NanoBeam 5AC-19 radios from Ubiquiti Networks (product page). This is a great little 2×2 MIMO 802.11ac radio, and very clean looking. I especially like the mount, which consists of a ball joint and a hose clamp. It’s very easy to install with only two hands, which is the most common number of hands. Many radios use a u-bolt and/or pipe clamp, and can elicit many profanities if you have less than three hands. Both radios are about 20′ above ground level to clear trees and vehicles between the buildings. I always leave loops of extra cable at both ends; you never know when you might need 5 extra feet of height, a connector will need to be replaced, or a power supply will need to be moved.

New office radio

New office radio

 

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Close-up of office radio

 

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Batch plant radio

 

Close-up of batch plant radio

Close-up of batch plant radio

 

Batch plant POE injector

Batch plant POE injector

I always make my cables as neat as possible – sometimes it goes unnoticed in the preexisting mess. In spaces like this batch plant, I don’t always have much to work with, but it’s best to keep everything out of harm’s way. Keeping cables and power supplies immobile also helps to maintain the integrity of your cables, crimps and connectors.

I set the transmit power to 0 dBm on both ends, and the received signal level ended up at -48 dBm. Transmit rates were solid at 8x (256 QAM). I used a 10 MHz channel. Links like this should be engineered to achieve maximum throughput by running at the maximum modulation rates; I believe “spectrum politeness” dictates that channel sizes should only be increased if the maximum modulation is already achieved, but the throughput is not meeting requirements. That said, 300′ links don’t really require much engineering or design. For someone with experience with wireless systems, these types of links are very straight-forward.

Here are the Ubiquiti internal speed test results, taken with a grain of salt as they use UDP and I’m not sure if they are over-the-air speeds or can be compared to ethernet speeds. Internet speed tests achieved the connection’s max speeds.

RX speed test

RX speed test

 

TX speed test

TX speed test

One thing to note: if you are upgrading these radios from AirOS v7.0.x to v7.1.x, you must first upgrade to v7.1-RC and then on to the newer versions.

Thanks for reading!

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