Lessons Learned from a Narrowbanding Project
July 27, 2011
By John Larribeau
Officials from Spokane, Wash., who have completed a narrowbanding project, submitted the following suggestions. The city’s 650 VHF and UHF radios were modified during the project. The city's 1,000 public-safety radios are being transitioned to an 800 MHz network.
1. Licensing. As one of the first steps, we modified our existing licenses for dual emissions both wideband and narrowband. With the dual status, we were covered during the transition when some radios were using wideband and others had been switched to narrowband. Also, the FCC doesn’t require additional license modifications when the switch is complete. The wideband emission designator will automatically fall off the license Jan. 1, 2013.
2. Asset Inventory. An accurate inventory will ensure all radios get modified. With an accurate inventory, you can figure out how many radios aren’t narrowband capable and must be either removed from service or replaced. The sooner this is done, the more time you have to shop for the best prices for the replacement radios. The inventory also provides an indication of your progress during the project.
3. Testing. I can’t stress this enough. We tested each model radio on the bench well before the actual switch to see just what was required and the best way to do it. Finding problems once you’ve started the project can be a disaster for your timeline and add frustration to the operators and users. We identified many problems and came up with corrections or workarounds during testing that allowed our actual switch to come off without a hitch. We researched each model of radio in our inventory and then tested it to see if it would go narrowband as advertised, and if so, what additional steps were required. Some models required us to adjust the deviation up or down in addition to just switching the bandwidth to be close to the 2.5-kilohertz target. We also made sure that we had all of the necessary software and programming cables on hand to do the job.
We also looked at the job itself. How long would it take to reprogram one radio using various methods? We converted one of the radio shop’s service vehicles into a mobile lab just for this project.
4. Planning. The timetable for the project took considerable planning. This is where all the work before the actual switch took place. All of the radio change-outs took place here. With our citywide system, we could do the actual switch two different ways. The first was to switch half of our voted receivers to a different PL/CTCSS code and load the new code into the radios when they were switched to narrowband. This would allow us to take our time with the conversion because both wideband and narrowband radios would work on the system without great variances in the audio levels. This would, however, limit the coverage and range in some areas.
The second option was to accomplish the whole switch over a weekend. This had a number of advantages for us. It allowed us access to most, if not all of the radios — only emergency crews were in the field. We conducted over-the-air testing without major disruption to users and produced the minimum interference to normal operations. The down side was the technicians’ long hours. However, we chose this option and were pleased with the results.
5. Coordination. Coordination is vital if the project is to be accomplished smoothly. All network users and managers need to know what is going to happen and why. They also need to be aware of what to expect (10 – 20 percent reduction in range) after the project is completed. You will need access to and the keys to spaces and vehicles to accomplish the modifications. Being locked out of a space or not being able to start vehicles to reprogram the radio can halt your progress and add extra time to the follow-up/cleanup portion of the project. As an example, we reprogrammed our largest department with 181 radios in one weekend. Four missing radios were corrected on Monday. This department broke down to about 69 percent mobile radios, 29 percent portable radios and 2 percent base repeaters or voted receivers.
6. Execution. The night before the actual switch, all of the equipment was assembled, tested and loaded. Final calls were made to all the various points of contact to verify that everything was in place and confirm when and where to meet at the start of the project. Because of the planning, portable radios were delivered or staged at a location where we had access to them for the switch. Vehicles with mobile radios were available with the keys or were delivered to one of our primary staging locations. It was easier and more cost effective to stage heavy construction equipment at a few locations and have our mobile lab go to them, rather than having them delivered to us. Because of this, we spent the majority of our time working on the equipment and not hunting it all down.
7. Cost Savings. With the state of our economy, you have to take a serious look at costs. Here are a few things to consider:
Set up mobile labs. Our mobile lab was accomplished fairly inexpensively. A Ford Ranger was equipped with a 1-kilowatt power inverter to power a service monitor and a 12-volt DC (VDC) tap to power the computers and other 12-volt accessories or radios. The computers were old police mobile data computers (MDCs), which we reused for this project. We used two to save time because some radio software was disk operating system (DOS) based and some was Windows base. Although we had the capability to reboot the MDCs in DOS mode, it took too much time, adding about 3 – 4 minutes to the process each time we did it. The total cost for the mobile lab was $210 with the main cost being the inverter.
Get extra programming cables. Although we already had all of the programming cables and software, we wanted extras and spares so we could do multiple sites simultaneously. We found after-market/knock-off programming cables on the Internet at a huge savings. We also found radio interface boxes at an equally huge savings. Have multiple setups with spares so that one broken cable doesn’t stop the project cold.
Coordination and weekend execution.This was probably the single, biggest cost-savings measure. We easily saved between 50 percent and 80 percent in labor alone by doing the project over the weekend. This takes into account that the technicians were paid overtime during the weekend. The time involved in trying to locate vehicles, bring them in, find keys, find portable radios and not have a mobile lab adds expensive, unproductive time for the techs.
Over-the-air testing. With our mobile lab, we were set up to fully test and align all aspects of the communications system. This included power, voltage standing wave ratio (VSWR), antenna tuning, receiver sensitivity, squelch, CTCSS levels, deviation levels and frequency. The frequency tolerance of a radio is cut in half when you go to narrowband. Some of our radios required adjustments in this area. We fabricated umbilical cables, which consisted of 2 RG-8M to BNC RF cables and a CAT-5/6 cable (data/microphone line) with a coupler for programming and microphone connections. We could program the mobile radios through a 50- or 100-foot extension cable with no problem. We could read the deviation with the same accuracy through the antenna port on the service monitor by connecting it directly to the RF in/out jack. We still had to connect the portables directly to the service monitor, because the deviation reading from the portables was erratic from inside the cab of the service vehicle. This saved time in connecting and disconnecting the RF cables to the radios. With the coupler on the data cable, we could connect and disconnect the programming cables, microphones and test set from inside the cab of the service vehicles.
John Larribeau is the electronic communications systems technician for Spokane, Wash. He has 26 years of service in the U.S. Navy and worked for 15 years as a senior manager for Radio Shack. Contact Larribeau at firstname.lastname@example.org