Engineering Radio – Page 110 – One Hundred percent Human Generated Content for your Reading Enjoyment

The Harris Z6HD transmitter

These transmitters are good. They seem to behave in a mostly normal manner, having a few quirks now and then. This particular unit is installed at WFAS-FM in White Plains NY.

Harrsi Z6HD transmitter, WFAS-FM, White Plains, NY

I believe the reason for the installation was for the HD Radio® that was in it. The Deathstar HD Radio® exciter is in the next rack over. No further comment is needed.

On this day, the transmitter had given up, throwing a main fan fault. The fan (blower) motor had been replaced in the last six months (on a transmitter that is only five years old), so it was not that. As it turns out, the stock fuses; 10 amp, slow blow, were just a little bit underrated for the job. Harris released a service bulletin a few years ago calling for 15 amp slow blow fuses as replacements. In any case, it was an easy fix and now there is a box of 15 amp slow blow fuses in the transmitter next to the fuse holders.

Harris Z6HD transmitter front RF modules

The modules are accessible by the front and rear of the transmitter. These doors can be opened with the unit on the air since all of the high voltage is in the bottom of the transmitter where the blower is located.

The module in the middle is the IPA. Each module has two RF amps, and each RF amp has two devices (BLF-177). The devices are field replaceable, however, on the HD models, one has to make sure that the amplifiers are still linear. On the non-HD models (Z6CD), this is not a problem at all. Shorted MOSFETS will be noted by a fault of one entire power supply. Removing the bad RF module will allow the transmitter to run at somewhat reduced power. Finding the bad module may take a bit of trial and error.

The back of the transmitter has the directional coupler, low pass filter, access to the back of the analog exciter, controller, and remote control connection points.

The power supply at the bottom of the transmitter has multiple taps, each one with its own fuse. These can be a bit of a chore to work on. There is also a ribbon cable that goes from the controller to the power supply board. This is directly in the path of the cooling fan and can flop around causing the conductors in the cable to break. The result is the power supply may not come on or may show an unbalanced power supply condition (in the case of a three-phase transmitter). Very difficult to diagnose.

Harris Z6HD transmitter, on air, WFAS-FM, White Plains, NY

Here it is, running again.

Lightning season

Here in the northeast, there are seasonal variations in the types of weather phenomena encountered. Blizzards in the winter, severe thunderstorms, and the occasional tornado in the summer, at least that is the way it normally happens. This year, we have already had two thunderstorms and a stretch of unusually warm weather. My highly advanced personal weather prognostication technique consists of looking at trends, and the trend thus far this year is warmer with more storms.

When the weather RADAR looks like this, it is too late.

To that end, it is time to go around and check all of the grounding and lightning suppression methods at various transmitter sites and studios. I would rather spend a few minutes extra now than get called out in the middle of the night for an off-air emergency related to a lightning strike.

Proper grounding of all equipment, RF cables, and electrical service entrances is the minimum standard for transmitter sites. Proper grounding means a common point grounding system connected to one ground potential.

To that end, all coaxial cables that enter the building need to have their outer shields bonded to the site grounding system at the base of the tower and the entrance of the building. With an FM station where the antenna is mounted at the top of a tall tower, the coaxial cable outer jacket acts as an insulator along the length of the tower. A lightning strike on the tower will induce a very high potential on the outer conductor of an ungrounded transmission line. After entering the building, the lightning surge will find the next path to ground, which will likely be a coax switch or the transmitter cabinet. Neither of those two outcomes is desired.

Thus, it was time to ground the transmission lines at WRKI, the FM transmitter we moved last January.

Fortunately, Andrew, Cablewave, Dielectric, and others make grounding kits for various size coaxial cables. They are very easy to apply and make a solid connection between the outer conductor and the site ground.

The kit contains a copper band bonded to a ground wire, stainless steel clamp, waterproofing, tape, and a pair of bolts.

The concept of transmitter site grounding is pretty simple and inexpensive to implement. Thus, it is surprising to me how many transmitter sites, especially older sites, do not have adequate grounding. That is an accident waiting to happen.

For more on transmitter site grounding, check Nautel’s publication (.pdf) “Recommendations for Transmitter Site Preparation.”

GPS Jamming devices: FCC says No!

The FCC has become concerned about Jamming devices for Cellphones, GPS and WiFi. So much so, they have released Enforcement Advisory No. 2012-02, which specifies fines in excess of $100,000 per incident.

The advisory states:

In recent days, there have been various press reports about commuters using cell phone jammers to create a “quiet zone” on buses or trains. We caution consumers that it is against the law to use a cell or GPS jammer or any other type of device that blocks, jams or interferes with authorized communications, as well as to import, advertise, sell, or ship such a device. The FCC Enforcement Bureau has a zero tolerance policy in this area and will take aggressive action against violators.

I have ~~two~~ three thoughts:

GPS jammers are increasingly being employed by those who are concerned about their privacy. That set of people can range from truckers who don’t what their bosses to know every aspect of their journey, citizens concerned about GPS tracking devices on their vehicles, or ordinary people who don’t want the phone company tracking their every move via GPS-enabled cellphones.
If only the FCC were as diligent and judicious in pursuit of other interference issues in the radio frequency spectrum. A few immediately spring to mind; IBOC to analog adjacent channels, broadband over power line, electrical noise on the medium wave band, illegal 2-way radios on RPU frequencies, etc. Of course, there is no money in those issues.
Wasn’t the FCC about to allow LightSquared to install high-powered 4G data transmitters all over the place, thus jamming GPS anyway? I know they nixed that plan after the general uproar over the loss of GPS by things like aircraft in flight, etc.

It remains to be seen how, exactly the FCC is going to find things like this:

Hypothetically speaking, in a mobile operating environment while traveling down the interstate at 70 MPH with thousands of other vehicles, it would be the proverbial search for a needle in a haystack. This would be especially true for a GPS-only jamming device, which would require a very small amount of power to jam the weak satellite signals. It presents an interesting problem for the cash-strapped enforcement bureau.

Not all jamming devices are this small, however. After doing a Google search for GPS jamming devices I notice that some of them are great big honking things, with heatsinks and fans, capable of generating large signals on every cellphone, WiFi, 3/4G, and GPS frequency. Those larger jamming devices would be very easy to locate and disable.

Perhaps if the technology wasn’t so pervasive and readily abused by certain corporate and government entities, the desire to jam it wouldn’t exist.

Why be a Broadcast Engineer?

That question was posed to me this afternoon by a coworker. It is, indeed, a good question. Certainly, broadcast engineering is more of a vocation than a career, especially where it concerns radio stations. Why would anyone work for low wages, long hours, little or no recognition, 24/7 on-call, and or unappreciative management?

Further, in this risk-averse, zero-defect, micromanaged environment, what is the upside to being a radio, RF, or broadcast engineer?

I suppose one would have to have some appreciation for history. One of the reasons I cover radio history here or certain historical events is that without knowing the roots of radio, one would be hard-pressed to find today’s version of radio broadcasting even remotely interesting. Understanding that before there was the internet, web streaming, Spotify, Youtube, Sirius/XM, television, cellular telephones, 3G, 4G, and so on, radio was mass media. Radio was people-driven, and people-oriented, not an automated computer programmed from afar. People tuned in for the music but also the personality and the personal connection.

Growing up in the late sixties and seventies, radio was my link to the outside world. As a young boy living in rural upstate New York, my mostly agricultural surroundings seemed a bit provincial. Through radio, I was able to listen to the clear channel stations from New York City, Chicago, Detroit, Nashville, Charlotte, Pittsburgh, Washington DC, Cincinnati, etc. The street that I grew up on did not get cable TV until 1980, prior to that, the rooftop antenna received exactly two channels when it wasn’t blown over by a storm. The black and white TV was often broken, sometimes for over a year. It was of no great consequence, however, when nightly under my pillow, the battery-powered transistor radio was employed until midnight or later.

When I got older, shortwave radio kits were built and listened to.

Through that medium, I learned about life outside of my small town.

Author, sitting in front of Atwater-Kent Model 20 regenerative receiver

The upside is being a part of something that can still be great, although those stations are getting harder and harder to find. Still, there is a certain pride to a job well done, a clean transmitter room, and a well-tuned machine working into a properly tuned antenna. Does anyone even appreciate that anymore? I do. Lou Dickey, John Dickey, Bob Pittman, Leslie Moonves, and other CEOs may not care that the transmitter site is clean and well-kept. They may, in fact, question it as a waste of salary. I appreciate it. Fellow engineers will appreciate it, too.

Starting a transmitter, especially a high-powered tube transmitter, is a joy all its own. Nothing against Nautel, they make fine transmitters, however, when pressing the on button, the outcome is almost assured: The transmitter will turn on. Not so with certain tube-type transmitters. Pressing the plate-on button for one of those can have many different outcomes. There is a certain thrill when it all works right, the first time. There is a certain pride in driving away from a transmitter site, listening to the radio, and knowing; I caused that to happen.