Pre-install testing your PTP820 gear. An hour in the lab can save a day or more of frustration.

A word on lab testing Licensed Point to Point (PTP) gear.

There are few things as disheartening as finding out that the piece of equipment that an expensively hired contract climber just hauled up the tower won’t power up, or won’t link, or is the wrong item due to an ordering error.  All of these expensive and project delaying scenarios are avoidable with some prior testing.  In fact, I can’t stress enough the importance of firing up the gear on the ground, working out the configurations and making sure the correct capacity licenses are on hand and installed.  Having all of this done in advance gives great confidence in getting the link up and running to a customer’s satisfaction.  That said not all gear is easy to test on the ground.  Let’s take the case in point, the PTP820C, 820S, and 820G split or all outdoor radios.  All of those radios use interfaces between the RF unit and the antenna that most shops just don’t tend to have laying around.  One of my peers Dave Hensley came up with a nice parts list if you want to assemble a benchtop test kit – you can find it here: 

https://community.cambiumnetworks.com/t5/Licensed-Microwave/PTP-820-RF-Staging-Kits/m-p/48978?advanced=false&collapse_discussion=true&filter=location&location=forum-board:forums_ptp_820&q=staging&search_type=thread

The kits that Dave Hensley identified are the best ways to test the radios.

But let’s say the gear has arrived and the expectation has been set – the gear gets installed next Monday – not near enough time to acquire all those parts.  What can be done?

The first problem you will see is that the PTP820S, C and G radios with the current as of this date firmware of version 10.5 has a minimum power setting of 1dBm.  This means that with even just a 1’ antenna at 18 GHz you will develop more RSL than a link of less than ¼ mile can handle and operate cleanly.  So, what are the options?  These options all assume you are running at the minimum 1dBm output power.

  1. Sometimes with the radios right next to each other, and the two antennas placed face down on the ground can yield an acceptable signal level.  This often does not work indoors as metal and concrete can be too reflective, but actual dirt earth can work.
  2. A really professional approach might be to use a real RF absorptive material like Ecchosorb between the antennas. It’s not cheap, but it allows many higher-powered radios with integrated antennas to run at full power with only a slice of Ecchosorb AN-77 sandwiched between the antennas.  At 5 GHz is was figured that on sheet of AN77 was the same as about ¾ of a mile of free space loss – with no reflection issues.  You can find Ecchosorb here:  http://www.eccosorb.com/products-eccosorb-an.htm
  3. Antennas can be deliberately mis-aligned. This can work but be careful as reflections in a metal building might make this impossible indoors.
  4. You can experiment with what you have on hand. In my photo my sweater gave us 1dB of loss at 18 GHz, and the folded rubber floor mat gave 4dB or loss.  My photo shows the sweater and floor matt approach.  Just don’t put anything with metal in or on it in front of the antenna.

When testing a PTP820 link that is too hot (too much signal level) you’ll see high numbers of defective blocks when observing MSE.  A link in this condition CAN pass management traffic, but the main carrier T-1 or Ethernet traffic may not pass at all until the RSL level is reduced to acceptable levels.  Being able to see and manage the far end radio is an indication that you are getting close, but still need to lose more RSL. 

Once you get the signal level right, the MSE block errors will cease and traffic should be flowing.  If not, be sure and go through the configuration again and make sure the PIPE or VLANs are all correct and that everything else on the bench is set to work with it.  An hour or two getting it right in the lab may save days or more of frustration in the field.

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A photo of my "McGyver" PTP820 Testing.  In case you are wondering, my sweater give 1dB of loss at 18 GHz, and the floor matt added another 4dB of loss.

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