Webinar Q&A: BDA Testing

We received many great questions from the audience during the webinar, “BDA Commissioning Tests: Ensuring BDA Performance and Compliance with FCC and Radio System Requirements” on June 20, 2024. We weren’t able to answer all of them during the live Q&A, so we’ve provided additional answers here. Answers are by the webinar panelists: David Adams, PCTEL’s Director of Market Development and President of the Board of Directors at the Safer Buildings Coalition, and Tom Warfield, Training Manager at Fiplex by Honeywell.

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PCTEL offers a BDA testing kit for the PCTEL public safety testing solution, which includes automated testing and grading capabilities discussed in the webinar. Please contact us for more information.

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Q) Which tests should jurisdictions require?
David Adams: Best practices are for jurisdictions to require all of the tests we discuss in this webinar. A comprehensive testing program makes it much easier to ensure BDAs function properly and don’t interfere with the outdoor network, or with other BDAs. For more information about these tests, you can consult the the Safer Buildings Coalition’s ERCES handbook.

Q) When you are measuring for leakage outside of the building, how do you differentiate leakage versus what is coming from the donor antenna?
David Adams: Use the Test Transmitter to create a CW signal on an unused (clear) frequency – then measure both the test signal and the Donor Site signal.

Q) Can the PCTEL Grid testing option capture Analog UHF, where there is no active Control Channel? I understand the Grid Testing captures an average signal strength at each grid. How would this be accomplished with an Analog UHF system with no active control?
David Adams: Yes. We have a method to measure “Maximum” (or peak). This is used for traffic channels of any technology. You have a choice of measuring all channels in a group until one channel is activated by a real user OR using a test radio to trigger the channel to be turned on.

Q) What is the small generator that comes with the backpack unit used for?
David Adams: It is a Test Transmitter to create a CW signal.

Q) What is the maximum signal and distance allowable for exterior leakage as per NFPA?
Tom Warfield: I don’t know of any NFPA requirements. This seems to be a test initiated by individual jurisdictions.  Those jurisdictions vary in requirements. I know of one that doesn’t allow any signal power from the ERCES to >-75dBm outside of the building.  Another requires the ERCES signal to be >15dB lower than the tower’s signal power. The distance from the building is usually 3 feet from any entrance/exit to up to 15’ away. The goal is to prevent time delay interference for emergency vehicles when they pull up in front of the building.

Q) So the center frequency is the control frequency, and we need to “sweep” ±75 MHz?
David Adams: When sweeping the BDA to document the configuration, sweep the whole band that the BDA covers. For example: use 806-815 if all the channels are between 806 and 815.

Q) Slide 13 – Do you have any recommendations for time varying noise measurements (i.e. those that vary depending on the time of day)?
Tom Warfield: A spectrum analyzer that has a waterfall capture mode is usually best to capture when interference occurs. Or, any device that constantly records measurements with a time stamp.  Hopefully, a trend will emerge of when the interference happens during the day.
David Adams: Additionally, PCTEL’s SeeHawk™ Monitor can watch the spectrum continuously, detect noise events, and capture the spectrum over time for replay.

Q) Any advice on making uplink measurements on a simulcast system? Can we test for uplink with he test equipment? Do you have anything to detect nuisance BDAs?
David Adams: The methods were mentioned early in the presentation: A person at the site with test equipment or someone can access the radio management system to get a power (RSSI) value. We do provide a system (SeeHawk™ Monitor) that can do this automatically without a person involved and gives signal quality as well for P25 (soon to add Analog). This system can also be used to detect noise and interference, including BDA problems.

Q) Please clarify who we mean by “licensee” in a public safety environment.
David Adams: The person that was given a “license” to use assigned frequencies by the FCC.
Tom Warfield: For first responder networks, that “person” is usually the county or sometimes the city.  A person is then assigned to perform the duties.

Q) Please address how utilizing a class A BDA affects the off-channel noise in the DAS.
Tom Warfield: A Class A BDA will only amplify what is in each channel’s passband.  If a filter is 75kHz wide, it will amplify the channel (usually 12.kHz wide) and 37.5kHz on either side of the center frequency. If the noise is more than 37.5kHz away, it will not be amplified.  Setting the passband of a Class A filter is always a compromise of interference rejection (the narrower, the better the interference rejection) and delay through the filter (the more narrow the filter, the more delay).

Q) On Slide 23, it shows “signal on monitor port on Rx Path.”  Do most manufacturers of P25 or trunked systems usually have a monitor port in-line without having to disturb (i.e., disconnect) the Rx antenna cable to insert your own power divider?
Tom Warfield: This is beyond my area of expertise. There are numerous manufacturers of combiners/multiplexers that can be installed at the shelter below the tower. However, it isn’t uncommon to have unused ports on the multiplexer that can be used. This is because these combiners/multiplexers are usually configured in multiples of 2 (2-way, 4-way, 8-way, 16-way, 32-way, etc).  The designer will choose one that has more ports than channels being used.  Network protocols (digital/analog/trunked/conventional) all have combiners/multiplexers to combine all the channels to use one coax from the shelter up to the antennas.

Q) Is there any sort of inspection tag for annual testing?
Tom Warfield: That is up to each individual jurisdiction’s requirements.  I have seen them implemented, but more often than not, they are not required.

Q) If you don’t know UL path losses/gains at the transmitter site, or if it is not provided by the AHJ, what’s the best way to estimate these gains/losses?
Tom Warfield: That is the $64,000 question. Most towers will have some uplink offset as compared to the downlink. If I had to guess, I wouldn’t want to assume there is more offset than there actually is. Otherwise, my calculations might make the RX signal power too low. Therefore, I’d assume only a 3 to 5 dB offset. If I am wrong and there is none, then I’ll only be 3 to 5 dB low.  If there is more of an offset, then, I am calculating too strong of a signal, which probably will be okay. You won’t see this in any codes, but here is my advice. Insert a variable attenuator between the portable and antenna of the portable which is being used for a DAQ test. Add attenuation until the uplink DAQ out of the building is just beginning to fail.  Calculate the output power of the portable minus the attenuation. Use that as a starting point and add a margin of safety so that the BDA puts out maybe 15 to 20 dB above that channel power.

Q) I would like to ask if a BDA is specified with the second or third order distortions and 1dB saturation?
Tom Warfield: Those parameters are measured; it is part of the FCC acceptance testing of all BDAs sold in the USA.  Whether or not the BDA OEM makes the results available is totally up to the manufacturer.

Q) In general, is the DL & UL path loss different?
David Adams: The loss between Donor Antenna and Donor Site Antenna will not vary much except for the location of the antennas on the Donor Site Antenna and any possible “clutter.” When you add the Donor Site cabling, amplifiers, etc. there can be a substantial difference.

Q) Could you explain the difference between path loss and link budget?
David Adams: The link budget is all the additions and subtractions. The path loss is the resulting value.

Q) Have you done any cost benefits for a BDA in the building?
David Adams: In the case of Public Safety or Business Mission Critical, the primary benefit is increased safety from reduced risk.

Q) Don’t you already need to have understood/established the D/L-U/L offset long before now if your testing was accurate?  If you did not properly understand this at the time of testing, you likely installed “too much” BDA.
Tom Warfield: In an ideal world, all parameters of the network would be fully understood. However, when you say “testing,” in most instances, we cannot test uplink; we have no access to the RX signal received by the base station. As for calculations, since the national codes only require downlink ERP from the tower, usually that is all we get. Uplink/downlink link budget imbalance is hardly ever given as well as BTS output power. There are many people within the BDA ecosystem that complain that BDAs are not set up properly and yet most jurisdictions do not give us the information we need to do it accurately or the ability to test. I’m not sure what you mean by “too much BDA,” but I interpret that as downlink output power. We know what downlink output power to design for based on ERP and the link budget, which we can measure as the received signal. It is the uplink where the issue is. Most BDA OEMs only offer one uplink power amplifier option (in case of Fiplex, all our PAs are +24dBm for all products, all bands). Therefore, you cannot get too much BDA, as it is what it is.

Q) Are we using the spectrum analyzer to generate the signal and reading it using the PCTEL?
David Adams: With the PCTEL provided equipment, we use a separate Test Transmitter to create the signal and the Test Kit to measure and record.

Q) For that first image showing the antenna shake down, are you using the PCTEL? Is there any direction that shows you how to do that on the PCTEL website?
David Adams: Instructions are in the User Guide included in the software, but we do not currently have a video on the website. We will cover this in our new User Group meeting scheduled for July 24, 2024.