Category Archives: Best of Site

Longer articles featuring the best of Biographies of local engineers, news event coverage, and “Making Waves” commentary.

Stubs for Fun and Profit

A year ago I was helping out temporarily at Bext with technical service and a number of interesting challenges came up. One was from a customer whose low power FM transmitter shared a site with a mobile carrier. The carrier’s technician was complaining about the transmitter’s 8th harmonic getting into his  radios. The FM transmitter in question was clean far beyond FCC requirements of -80dB below assigned carrier level (as I remember, about -96dB) but on a spectrum analyzer, you could see a tiny bump down near the noise floor in the 800 MHz band. I used the analyzer and its tracking generator to trim a hunk of coax and knock down the 8th harmonic of the offending FM transmitter about 20 dB. That’s a pretty short piece of coax, by the way. Problem solved and nobody had to build a Faraday cage.

A June article in the BDR mentions this conflict between the very sensitive LTE mobile site receive inputs and their FM transmitter neighbors. These radios are attempting to discriminate data at -120 dBm and lower from distant tiny transmitters inside metal cars and buildings.

I first ran into an application for a stub with a TV translator site in the Oregon high desert in the early 80’s, where I was receiving a faint UHF signal beyond line-of-sight and picking up some birdy from my channel 5 output. With an N-connector “T” adapter and a quarter-wave length of RG-213, I fashioned an open-ended stub that resonated at the mixer product, attenuating it enough to remove the problem from the visual band of my UHF input.

Another recent article in Radio World magazine, this by Mark Persons, suggests putting a bandpass filter in the form of a quarter-wave shorted (not open) stub after a solid-state amplifier feeding a tube amplifier. This is brilliant. It serves to attenuate voltage spikes that might enter since only the resonant frequency passes without great loss–DC and pulses slow and fast are shorted out. By the way, this won’t work with TV or other broadband applications due to the high-Q of the stub.

Check out articles on construction of these stubs online.

Tijuana Analog TV Stations Sign-off

UPDATE 7/22/2013 – Analog stations along the border are now off the air, apparently permanently after elections. 

UPDATE 5/13/2013- Analog stations along the border are back on the air today after electoral candidates complained about lack of exposure ahead of July 7 elections. 

Eight Tijuana TV stations went dark May 28, 2013 as the first broadcast market in Mexico to go all-digital, delayed a month from the previous target date of April 16. Those stations included:

  • XHTJB channel 3, affiliated with Once TV, public/educational
  • XETV channel 6, Televisa O&O, affiliated with Canal 5
  • XEWT channel 12, Televisa O&O, affiliated with multiple networks
  • XHTIT channel 21, TV Azteca O&O, affiliated with Azteca 7
  • XHJK channel 27, TV Azteca O&O, affiliated with Azteca 13
  • XHAS channel 33, Entravision operated, affiliated with Telemundo
  • XHBJ channel 45, Cadena owned and Televisa operated, affiliated with Galavision
  • XHUAA channel 57, Televisa O&O, affiliated with Canal de Estrellas

Notably, XETV had just celebrated 60 years of broadcasting, having signed on with English language broadcasting in 1953 and continuing to do so until last year, when it switched to Televisa’s Spanish-language broadcasts of Canal Cinco. XETV-DT was the first digital TV station to broadcast in Mexico in 2000, and likely the inspiration for having Tijuana selected as the first market to shutdown its analog TV.

Mexico’s EFE indicates that over 192,000 free digital TV converters were passed out to Tijuana area residents as part of the transition. Unconfirmed statistics have 48% of Tijuana residents receiving their TV via free over-the-air broadcasts.

Interestingly, Entravision-operated XHDTV on Cerro Bola near Tecate remains on the air on channel 49. The next shutdown date, November 26, 2013 is supposed to include Mexicali, but it is not known whether XHDTV will shutdown at that time.

What is not yet known is how the empty channels will affect FCC-mandated repacking of TV channels along the border. There’s likely to be a scramble on both sides of the border to occupy the empty lower UHF channels.

Longtime XETV Engineer Francisco Laurent Passes

Francisco Laurent in front of XETV transmitter, 2009

Francisco Laurent Martinez, who served as engineer and Chief Engineer of the Transmission Department at XETV in Tijuana from 1959 till this month, passed away March 24, 2013 in Tijuana. He saw the facility progress from a single English-language ABC affiliate for San Diego to a cluster of eight Televisa-operated TV stations, all now with solid-state transmitters and antennas on two self-supporting 500 foot towers.

He mentored engineer Humberto Borzani, who told us Francisco was born December 7th, 1930 in Tijuana. He graduated in 1956 as an Engineer with a major in Electronics and Communications in Mexico City. He served as Chief Engineer of the Radio Monitoring Station of SCT (the Mexican equivalent of the FCC) from 1972 to 1987. The SCT sent him to Washington to coordinate cross-border frequency allocation studies in 1979.

Francisco served as professor at the Instituto Tecnológico de Tijuana from 1971 till 1987, and was founder of the associated cultural FM station Radio Tecnológico 88.7 MHz FM from 1987 till 2005.

XETV Tijuana Master Control, 1968, when they were an ABC Network affiliate. Francisco Laurent in foreground.

On a personal note, I worked at XETV’s U.S. operations from 2004 till 2010, but was always warmly welcomed at the Mexican master control and transmission site. I have never seen a transmitter site like the one Francisco led, from the marble floor at the entrance and master control rooms to the spotless transmitter rooms to the twice-filtered air and shiny copper transmission lines. The 1955 GE transmitter was ready for air until just a few years ago. Their UPS and generator backups kept the transmitters going without interruption for years at a time. Francisco was justifiably proud of that facility, and he will be missed.

What Happened to San Diego Broadcasters When the Lights Went Out

At 3:40 pm on September 8, Paul Redfield, Director of Technology at XETV, heard a faint click from his San Diego TV production control room. He saw the hall lights go out briefly, but the production room lights and equipment hummed along. A few seconds later the hallway lights returned as their 600kW generator kicked on, replacing the missing street power.

Outside, traffic lights went dark, creating lines of cars with drivers waiting to cross intersections tentatively, one or two at a time. Car radios heard either static, or silent carriers, or the rare voice trying to make sense of the electrical outage that seemed to be affecting listeners calling in from throughout San Diego and Imperial Counties, as well as southern Orange County and Yuma, Arizona, affecting 1.4-million customers total for up to twelve hours.
Continue reading What Happened to San Diego Broadcasters When the Lights Went Out

Lessons Learned in the Power Outage of 2011

Whether you’re talking about a flood, hurricane, snow storm, fire, or big earthquake, the same basic principles apply.

Don’t depend on being able to drive. Roads can easily jam when everyone is evacuating simultaneously. Not a good time to take that drive to a remote transmitter site for some unfinished chore.

Don’t depend on cell phones.
Most sites have backup power, but they can depend on good fiber feeds and be easily overwhelmed by unusual usage, and battery backup on some fiber feeds may go out after several hours. If you must communicate, SMS text traffic can often get through when voice traffic cannot.

Maintain your analog radio communications systems.
Your station should have charged handi-talkies available for emergency use, says KGTV’s Andrew Lombard, and if you still have mobile 2-way units, they can be life-savers during emergencies or even for conventional communications to distant sites. “If you don’t have a two-way 450mHz band radio system, get one. Buy it. Lease it. Borrow it. [Then,] keep your 2-way radio system in good running condition!”

Your POTS line may not work in an outage. The old days of battery-floated telephone lines are fading in favor of voice-over-IP systems often delivered by cable companies. Even AT&T delivers phone service over both fiber and copper pairs now.

Test often. Backup generators must be exercised regularly, although your pollution control district can severely limit your opportunities to test diesel units.

Consider solar backup. With creative design, modern equipment and low-power lighting, you may be able to operate indefinitely with solar panels, prioritized power management, and storage batteries. It’s expensive upfront, but you aren’t subject to pollution rules and you will eventually pay for the system with power bill savings. There are numerous companies out there who can finance the costs with your energy savings, but you need a supportive management willing to accept a 15 – 20-year ROI.

Manage your batteries. Says Lombard, “Keep all your batteries charged, have an inverter in your car for battery charging, keep a set of jumper cables in your vehicle, and keep a working 12V battery-powered spotlight in the vehicle.” Rechargeable batteries in infrequently used devices like broadcast radios or flashlights should be the newer lithium-ion (Li-Ion) polymer or low self-discharge nickel-metal hydride (NiMH) batteries. The latter are sold under the trade names Sanyo Eneloop, Tenergy Centura, Ultralast Hybrio, Maha Imedion, Energizer Recharge, RayOVac Hybrid, and Duracell Rechargeable Pre-Charged

Keep emergency food rations. This one may not be so obvious to those in better weather climates, but there are going to be times when stores can’t operate. Reminds Lombard, “Keep emergency supplies stored somewhere–but not in vehicles–and send them with crews when they go out on a breaking story that will take a long time or have someone available to run supplies out to field crews.” Emergency water supplies are always there if your station buys water in large jugs, but filters can work if you have a known source of fresh water.

Don’t depend on fiber or two-wire copper links.
In San Diego, some continued working and some didn’t. If a line uses a battery float, it may maintain power for a limited time. Operation of leased lines has become especially difficult to predict.

Consider auxiliary sites.
Especially if you already own or lease an alternative site, putting up a small FM transmitter can be relatively cheap way to stay on the air with huge redundancy value. The payoff for TV and AM can be diminished since few watch TV over-the-air now and AM usually requires expensive antenna engineering.

Communicate with management regarding your capabilities.
This issue deserves an article itself. What is your return on investment with backup power and/or an auxiliary broadcast site? Are you protecting your reputation with your listeners or viewers? Are you an emergency primary station? Are you willing to study pollution laws if running a generator? If you are considering solar and batteries as an alternative, how much will it cost you to partition your power load to run off-the-grid for an indefinite period? At the time of an outage, your general manager and corporate engineering managers must not be surprised by your preparedness level or your job may be on the line. If you have sufficiently informed them of a lack of funds for backup equipment, then they shouldn’t be surprised by your outage. On the other hand, if you were given sufficient money, your equipment should always be ready for operation.