Common CBRS installation parameters mistakes

When a CBSD registers with the SAS, its installation parameters need to be verified and signed by a CPI. We have noticed some inaccuracies in some of the installation parameters, and this list summarizes some of the most common mistakes.
We suggest you double check your existing devices, and pay close attention when installing new devices, as future changes of any of these parameters requires a re-registration of the device with the SAS.

  • Downtilt
    • A negative number means that the device is tilted up; a positive number means that the device is tilted down
    • The 450i integrated and 450m APs have a built-in 2 degrees electrical downtilt
    • If you install the 450i/450m AP with a 0-degree mechanical downtilt, enter 2 degrees in the field (this accounts for the electrical downtilt)
    • If you install the 450i/450m AP with a 2-degree mechanical uptilt, enter 0 degree in the field (the mechanical uptilt compensates for the electrical downtilt)
    • If you install the 450i/450m AP with a 2-degree mechanical downtilt, enter 4 degrees in this field (the mechanical and electrical downtilts add up)
    • The limit of the mechanical uptilt of 450i/450m is 5 degrees; this means that no values should be lower than -3 degrees in this field
  • Antenna height
    • Double check the height type and height value: a common mistake is to select AMSL (Above Mean Sea Level) as antenna height type, but enter the numerical value as if it was AGL (Above Ground Level).
    • When calculating the height as AMSL do not forget to add the mast height
    • Note that AMSL is the default value in the Excel spreadsheet. If you want to enter the value as AGL, do not forget to change the height type
  • For some devices, the antenna beamwidth and gain depend on the actual device (if it is connectorized or integrated, if it has an additional reflector or not, etc.), but for some devices there is only one correct option:
    • For the 450m the beamwidth is 90 degrees, the integrated gain is 16 dBi, and the external gain is 0dBi.
    • For the 450b high-gain SM the beamwidth is 12 degrees, the integrated gain is 20 dBi, and the external gain is 0dBi.
    • For the 450i integrated AP or SM the beamwidth is 17 degrees, the integrated gain is 19 dBi, and the external gain is 0dBi.
    • For the 450 integrated SM with no reflector the beamwidth is 55 degrees, the integrated gain is 8 dBi, and the external gain is 0dBi.

These and more antenna options are either automatically populated in the spreadsheet when a device is selected, or they are listed on the right-hand side in the gray section.

  • Sanity check the antenna parameters. For example, an antenna cannot have a 55-degree beamwidth and a 20 dBi gain.
  • The antenna gain the device registers with is the sum of the integrated gain and the external gain. The integrated gain is always automatically populated in the spreadsheet when a device type is selected; the external gain is manually entered, because a device could be connectorized, or a reflector could be added. Do not copy the internal gain in the external gain option; a common mistake is for example with the 450b SM copying the 20 dBi gain automatically populated in the integrated antenna column into the external gain column. The device would then register with a 40 dBi antenna gain instead of the 20 dBi correct value.
    Note that reporting the wrong antenna gain not only violates the CPI responsibilities, but it also may limit spectrum availability when the SAS calculates the possible interference footprint of a device. The SAS may reduce the grant’s EIRP if it calculates the device transmission with an incorrect (higher) antenna gain.
  • Double check the accuracy values. Any value is valid here, as long as it is lower than the actual delta from the reported coordinates.
    As a reminder, if the coordinates are accurately know, it is more beneficial to have the accuracy values as small as possible, as the SAS is going to assume the worst case propagation scenario within the circle created by the accuracy values.
    However, if a device is registered with the tool a day ahead of installation, using larger accuracy values gives the installer more flexibility in where to actually install the device. The grant would still be valid (no re-registration is required) if the device coordinates are slightly off compared to the ones used for registration, but still within the accuracy limits.
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This is extremely important information. I have pinned this topic, and we will also send email communication to this effect.

Why is Cambium requesting we add in the electrical downtilt when the SAS system only wants the mechanical downtilt? Is cnMaestro then removing electrical downtilt numbers before syncing to the SAS? My opinion is that the FCC really needs/wants the mechanical info since that sets the area pattern where electrical downtilt mainly changes the strength of signal downward and not change the geographic pattern like mechanical does.

This is a very important question. SAS is suppose to take the antenna type into consideration (I think). Can someone from Cambium clarify this?

This is a pretty easy concept to grasp. The SAS wants the TOTAL downtilt… so both electrical and mechanical. Changing the electrical tilt does change the coverage area and eventually the SAS will take the coverage areas into account when determining grant requests and power requests.

Wasn’t asking about concept. The way you reply comes off a bit like you are saying I’m stupid for asking.

Just looking for Cambium to look and confirm since I see it different from other vendors and in the SAS itself. Would be nice to hear Cambium confirm. Maybe they made a mistake, or maybe the other vendors we use made a mistake. Image from Google SAS.

SAS clipping

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Just carefully re-read the first post. Cambium’s already confirmed that the downtilt is the total mechanical + electrical tilt. If you think about this, logically it makes sense. Electrical tilt has a direct effect on the coverage area of the sector… same as mechanical tilt. Why wouldn’t the SAS require both?

You can find further discussion and confirmation of the electrical + mechanical downtilt needing to be included, confirmed by a Cambium employee HERE.

We have fundamental differences of how we think of things. So logically I disagree, which is fine.

I’ll wait for confirmation from Cambium rather than go back and forth multiple times trying to prove our point to each other. I can show you things as well that say different. Like the standards committee document that says electronic tilt is needed for an omni antenna, but doesn’t say it is needed for directional. Or the CPI training that says to measure with a level or inclinometer, which only gives the mechanical tilt. I don’t run a SAS so I can’t confirm final standards that were put in place. And the FCC only defined the need for “tilt” and didn’t define what that included so now this debate.

In the end, neither of us know for sure or know what happens between cnMaestro and the SAS. My CPI may need to set different info for Cambium vs our other vendors that just say mechanical. We can only follow what the vendor says is needed in their GUI to push to the SAS. I’m just asking for a double-check and confirmation since differs.

Both the electrical and the mechanical tilt affect the coverage, that is why cnMaestro asks for the sum of the two.
Things will potentially change when support of WInnForum Release 2 is introduced, where the device is allowed to send the SAS the actual antenna pattern both in azimuth and in elevation. At that point, if the device reports its pattern, the electrical downtilt will be already included, and only the mechanical downtilt needs to be entered. However, if the device does not report its pattern then both the electrical and mechanical tilts need to be accounted for.

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I’d like to disagree with the notation of the downtilt. Traditionally 0 is the horizon with - being below and + being above.

Why is the downtilt here being asked for as a positive number when it’s pointing down and a positive number pointing down? That’s complete confusion and backwards from how the industry normally does it.

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This is how it is defined by the WInnForum standard and it must be reported in this way to the SAS.

I tend to agree with you, and it makes more intuitive sense to have “negative” going “downward” or “below” the horizon.

They look at it like this: the term “Downtilt” incorporates the negative (i.e. down), therefore positive downtilt points downward, below the horizon, towards the ground.

This is the convention that was adopted by the rule-making body, so we must abide by it.