Paul Thurst – Page 38 – Engineering Radio

The Ubiquiti Nano-Beam

I installed one of these wireless links between two transmitter buildings recently. The Ubiquiti gear is not my first choice, however, the client insisted that we use this equipment likely because of its inexpensive nature (less than $65.00 per unit). My overall impression is so-so. They are fairly easy to set up; the AirOS is intuitive and easy to navigate around. I had to upgrade the firmware, change the default user name and password, assign IP addresses, subnet mask, gateway information, SSIDs, security parameters, etc. All of that was very easy to figure out. My grip is this; it seems the hardware is a bit plastic-y (e.g. cheap). I know some of the Ubiquiti models are better than others. I hear good things about the airFiber units but they still don’t compare to the Cambium/Canopy gear.

For this installation, I used the shielded Ubiquiti “Tough Cable” with the shielded Ubiquiti RJ-45 connectors and Ubiquiti Ethernet Surge Protectors. When making the Ethernet cables up, I made sure the shield drain wire was connected to the metal body on the RJ-45 connector. I tested everything with my trusty Fluke Microscanner cable verifier which also shows continuity for the shield. I am still not completely confident that the outdoor units will survive a lightning strike on the 898-foot (273.7 meter) guyed tower nearby. Time will tell.

The system has a wireless path length of about 200 meters plus another 60 meters or so of Ethernet cable. Latency when pinging the gateway across the entire network is about 3 to 4 ms (laptop>switch>nanobeam<->nanobeam>switch>gateway). The network is being used for remote control/monitoring of transmitters and backup audio via Comrex Bric link II IP CODECs.

screen shot; Nano Beam Air OS — screenshot; Nano Beam Air OS v7.2.2

On the plus side, the 802.11ac link is very fast; 650+ Mbps unwashed link speed is pretty impressive. Strip off the wireless LAN headers and that likely translates to greater than 500 Mbps goodput. Also, the inexpensive nature of these units means that we can keep a few spares on hand in case something does suffer catastrophic damage due to a storm. The AirOS v.7 is pretty cool with the RF constellation and other useful tools like airView (spectrum analyzer with waterfall display), discover, ping, site survey, speed test, traceroute, and cable test.

After installing the updated firmware, which fixes a major security flaw with the web interface, the link was established with three mouse clicks. After that, I ran speed tests back and forth for several minutes. Basically, the speed on the LAN is reduced because of the 100 Mbps switch. Even so, that should be more than enough to handle the traffic on this segment of the network.

Decommissioning transmitters

I was at a transmitter site a few days ago scrapping a Continental 814-R1 transmitter. I started thinking (always a dangerous thing) about how many of these units I have decommissioned over the years. It turns out, quite a few:

Make/Model	Year new*	Year removed	Station	Disposition
GE BT25A	1948	1994	WPTR	Donated/scrapped
Gates BC5P	1960	2004	WWLO	Donated
Harris MW5A	1982	2000	WLNA	Scrapped
Gates BC1T	1961	2001	WLNA	Donated
Harris FM20H3	1972	2001	WYJB	Scrapped
RCA BT1AR	1960	2001	WROW	Donated
Harris BC1G	1972	2001	WDFL	Abandoned
Harris FM20H3	1971	2005	WHUD	Scrapped
BE FM30A	1988	2005	WHUD	Cannibalized
Harris FM5G	1972	2008	WSPK	Scrapped
Mc Martin BF3.5K	1976	2011	WCTW	Scrapped
RCA BTF-10ES	1978	2011	WRKI	Scrapped
Gates BC1T	1964	2011	WINE	Scrapped
Continental 315F-R1	1985	2013	WVMT	Donated
Collins 813F	1975	2014	WKXZ	Scrapped
RCA BTA1AR	1965	2014	WCHN	Scrapped
Collins 813F2	1978	2015	WKXZ	Scrapped
Collins 830D-1A	1968	2014	WKXZ	Scrapped
Harris FM20H3	1972	2013	WYJB	Scrapped
Harris BC5HA	1973	2013	WROW	Scrapped
Harris FM10H	1971	2013	WMHT-FM	Scrapped
Harris FM2.5H3	1973	2015	WEXT	Scrapped
Mc Martin BF3.5K	1972	2014	WSRK	Scrapped
CCA FM5000G	1980	2015	WTBD	Scrapped
RCA BTF1E	1972	2016	WZOZ	Scrapped
QEI 695T3.5	1996	2015	WBPM	Scrapped
QEI 695T5	1996	2015	WBPM	Scrapped
Harris HT3.5	1997	2015	WUPE-FM	Scrapped
Harris Z5CD	1997	2015	WXPK	Cannibalized
Energy Onix SSA1000	2000	2015	WDHI	Cannibalized
Harris MW1	1982	2016	WPUT	Abandoned
Mc Martin BF1K	1982	2016	WSUL	Scrapped
Mc Martin BF3.5K	1982	2016	WSUL	Scrapped
Continental 814R1	1980	2016	WDBY	Scrapped
Broadcast Electronics FM35A	1986	2017	WEBE	Cannibalized
CCA FM-1000D8	1973	2018	WDLA	Scrapped
Collins 828E	1978	2018	WSYB	Scrapped
Gates BC-1H	1971	2018	WHUC	Scrapped
Gates BC-1J	1954	2019	WBEC	Scrapped
Gates BC250GY	1969	2019	WSBS	Scrapped
Nautel V-7.5	2009	2021	WSPK	Cannibalized
Nautel V-10	2007	2023	WHUD	Cannibalized
Nautel V-10	2007	2023	WHUD	Cannibalized
Harris FM1H3	1970	2024	WBEC-FM	Scrapped

*In some cases the “Year New” is a guess based on when the station went on the air. Before you write me and say “But model XYZ transmitter wasn’t made until 19XX, I did not look at every nameplate and write all the information down as I did this.

Like everything else, there is a process to this.

First, if the transmitter was made before 1978, the possibility of PCB capacitors and transformers exists. In the case of the GE BT25A, massive amounts of PCBs needed to be disposed of properly. According to current federal laws, ownership of PCBs and PCB-contaminated items cannot be transferred. Thus, the transformer casings were cleaned and taken to Buffalo to be buried in a PCB-certified landfill. Otherwise, most other transmitters, such as the RCA BTA-10, may have a few PCB capacitors and perhaps the modulation transformer. Those items can be disposed of by calling an authorized environmental disposal company like Clean Harbors.

The rest of the transmitter is stripped of any useful parts. Things like vacuum variable capacitors, rectifier stacks, blower motors (if they are in good condition), HV power supply contactors, unique tuning parts, whole control and metering boards, tube sockets, etc.

The remaining carcass is then disassembled and hauled off. I have a guy that will do this for relatively little money. He takes the transmitter back to his warehouse cuts it up, sorts the various metals out, and then takes it to the scrap yard. This includes cutting all the windings off of transformers and power supply chokes, sorting out the brass and copper tuning parts, etc. Thus, most of the transmitter is recycled. Things like vacuum tubes, circuit boards, and other plastic parts are disposed of as e-waste.

The 16 channel bi-directional STL

As a part of our studio build-out in Walton, we had to install a high-capacity STL system between the studio and transmitter site. Basically, there are five radio stations associated with this studio and the satellite dish and receivers are going to be located at the transmitter site.

The audio over IP gear is getting really sophisticated and better yet, more reliable. For this application, we are using a Cambium networks (Motorola Canopy) PTP-250 radio set and a pair of Wheatstone IP88 blades on either site. Since there is quite a bit of networked gear at the transmitter site, the IP88s will live on their own VLAN. The PTP-250s will pass spanning tree protocol, rapid spanning tree protocol, 802.1Q, and other layer two traffic.

The Wheatsone IP88A blades are the heart of the system. Not only do they pass 16 channels of audio, we can also pass 8 logic closures bi-directionally. This is key because we are shipping satellite audio and contact closures back from the transmitter site. The IP88A setup is fairly easy, once the IP address is entered. The web GUI is used for the rest of the configurations including making the connections between units.

Pair of Wheatstone IP88A AoIP interfaces

The switches are managed units. The switchports need to be set up via command line to pass VLAN traffic. There is an appendix in the IP88 manual that outlines how to do this with various managed switches. This is the most important step for drop-out free audio. The switchports that connect to the two radios are set up as trunk ports using either VTP or 802.1Q.

The PTP-250 radios were already on hand, new in the box. They are built really well and look like they should not break in a year or so. These particular units are connectorized, therefore an external antenna was needed. There are many such antennas, this system ended up with an RF Engineering & Energy 5150-5850 MHz dual-polarized parabolic dish with RADOMES. RADOMES are necessary to prevent ice or snow build up in the winter.

RF Engineering & Energy 5150-5850 MHz dual polarized parabolic dish with LMR400 jumpers

Since the path is only 3.37 miles (5.43 kilometers), I set them up with a 40 MHz wide channel. This is a rural, small-town setting. When I looked at the 5.8 GHz band on a spectrum analyzer, it looks fairly uncongested. These are MIMO single or dual payload selectable. I will try them as single payload units since the path is short and the band is uncongested. This should keep the throughput high.

Studio to transmitter site LAN extension

The PTP-250s use POE injectors in mounted in the rack rooms. CAT5e shielded cable with the proper connectors properly applied is a must for lighting protection. The PTP-250 units came with Cambium PTP-LPU lightning protectors. I also installed Polyphaser AL-L8XM-MA type N surge suppressors on each RF port of each PTP-250.

Engineers hate this

Apparently, this coaxial cable has a hot spot:

7/8 inch air dielectric coax with jacket melting off

The back story:

I received a text this morning that one of our client’s stations “had a lot of static on it, it might be off the air.” Upon arrival, I found the Nautel VS2.5 transmitter with 0 watts of forward power and an output network fault. Reset the transmitter and the forward power and reflected power increased together, triggering another output network fault. I was able to turn the transmitter power down to 100 watts, at which point it stayed on, with 50 watts reflected power. I also noted the dehydrator running continuously and 0 PSI line pressure.

Crap.

I wandered around the back of the building where the coax goes out to the tower and discovered the dripping plastic from the melted jacket. I reached up and first checked the cable to see if it was warm (it was not). Then I shook it and heard what I thought was water sloshing around inside. This is the original Andrew 7/8 inch cable from when the station signed on in 1972 or so. Very likely that further up the tower, something has chaffed through the outer jacket and shield, allowing water into the cable.

I drilled a small 5/32-inch hole at the lowest point in the cable before it enters the building. The result was a steady stream of water, which was aided by some additional pressure from a spare N2 tank. I let it drain while I ran down to town and got some lunch. I came back half an hour later, turned the transmitter on, and was satisfied to see 100 watts of forward power with 1 watt reflected. I ran the transmitter up to full power for a while, then deciding discretion is the better part of valor, and turned it down to half power; 820 watts which net 8 watts reflected power.

Needless to say, the transmission line needs to be replaced as soon as possible.