February 2011 – Page 3 – Engineering Radio

Which do you prefer, GPS or 4G data?

In some locations, it is apparently going to be an either-or situation if this is to be believed:

Representatives of the GPS industry presented to members of the Federal Communications Commission clear, strong laboratory evidence of interference with the GPS signal by a proposed new broadcaster on January 19 of this year. The teleconference and subsequent written results of the testing apparently did not dissuade FCC International Bureau Chief Mindel De La Torre from authorizing Lightsquared to proceed with ancillary terrestrial component operations, installing up to 40,000 high-power transmitters close to the GPS frequency, across the United States.

Sound vaguely familiar? Seems that LightSquared took a page from the iBiquity play book when it comes to dealing with the FCC. The article goes on to say:

On January 26, the FCC waived its own rules (emphasis mine) and granted permission for the potential interferer to broadcast in the L Band 1 (1525 MHz—1559 MHz) from powerful land-based transmitters.

A little research on the LightSquared website shows they are rolling out an extensive L band 4G data network, not exactly what I would call broadcasting, at least not yet anyway. GPS system inhabits 1559 – 1610 MHz, centered around 1575.42 Mhz in the L-band. The signals coming from GPS satellites are very, very low, with the open sky signal around -130 to -135 dBm. Indoor signals can be as low as -150 dBm. Further, GPS receivers currently in the field were not built to operate in environments with high levels of RF energy on nearby frequencies.

So, who uses GPS? Just about everybody, including the military, the aviation industry, broadcasters, and the general public. Think about all the confused drivers who can no longer find their way to the grocery store without Tom-Tom. By far, the biggest impact is likely to be the entire cell phone network, which depends on GPS for its multiplex timing. It seems very likely that LightSquared network will be installed on existing broadcast and cell towers, right on top of the current cellular tenants. Even if they work around this by providing better GPS receivers with high pass filters, many existing consumer and aviation GPS receivers will be useless.

The potential interference is charted here:

Interference to consumer grade GPS receivers

For FAA-certified GPS receivers, the data is worse:

Interference to FAA certified GPS receivers

The FAA-certified aviation receivers are more sensitive, therefore, more likely to be impacted.

It makes me wonder, what is going on in Washington?

UPDATE: March 3, 2011, KNX, Los Angles runs with the story: Planned 4G service could cause widespread GPS jamming

The Nautel ND-5 transmitter

This transmitter is about 10 years old. In ten years of service, there have been no failures. Not one transistor has gone bad. It is connected to a three-tower directional array on 920 KHz.

Sadly, this model transmitter is no longer made. They were built like tanks, heavy gauge steel cabinets, well-designed, well-grounded circuit boards.

It is dirt simple; RF power MOSFETs on drawers, combined and tuned with the output network. A power supply, exciter, and simple control logic and nothing else. No serial port to plug a computer into, no ethernet ports, no digital read-outs, fancy efficiency optimizing computers, etc. In the meantime, it does what it is supposed to do, stay on the air.

I was reading, with interest, the idea of “energy star” transmitters. I think that good radio station engineers already take electrical efficiency into account when buying a new transmitter. That being said, electrical efficiency is not the only measure of efficiency an engineer should be considering. Reliability, redundancy, and repairability must also be considered. If the station spends an inordinate amount of time on the old backup transmitter while the new, super-efficient main transmitter is off line is counterproductive. Not to mention the time wasted troubleshooting which could be better spent on something else.

TIA/EIA 568

Radio stations more and more revolve around networked computers. Engineers need to understand computer networking, especially as it relates to audio distribution and playback. Eventually, I see broadcast engineers being more computer science types rather than electrical engineering majors.

What I have found out about computer networking is this: it is not rocket science. In fact, most of it is pretty easy. Physical networking and cabling are similar to audio and TELOC cabling. Automation computer servers themselves are not difficult to understand as most of them run on some type of Windows program. Other servers such as Apache for WWW and for FTP and streaming run on some type of LINUX OS. LINUX is also not difficult to understand so long as one knows the right command line prompts.

The first part of understanding computers is networking. Without a computer network, a computer is a glorified typewriter. Almost every automation system and or digital editor requires some type of network. Consoles and computers that use AOIP require well-constructed networks in order to operate properly. To that end; cabling choices, network interface devices such as switches and routers, patch panels, and so forth need to be specified and installed with care.

Most often, it is the simple things that will trip an installer up. The one area where I have found the most mistakes made is the pair’s connection to various termination points. There are two basic standards, TIA/EIA T568A and T568B. Neither is better than the other, both are often identified on terminating devices such as jacks and patch panels. The most important aspect of these standards for an installer is to pick one and stick with it.

When certifying networks, the most common problem I have encountered is crossed pairs. Almost invariably, one end will be punched down with the A standard and the other with the B standard. Jacks are particularly difficult, as the color-coding stickers show both. Many patch panels have a slide-out, reversible card with is an either/or situation. For some reason, I have stuck with the B standard, and on any project I am managing, I get rid of all the A color codes I can find and tell the installers that B is the only acceptable termination standard. That cuts down on a lot of errors and redos during certification. That is good, it saves time and I hate redos.

You can see that this color code marking can lead to confusion. I take a sharpie and cross out all the A markings to avoid installation mistakes.

Incidentally, on any new network installation, Category 6 cable should be used. As more and more data throughput is required for network applications, Category 6 Cabling has better performance specs and will likely have a longer service life than another cable. It may be a little bit more expensive than Cat 5, however, well worth the investment. It would be a great mistake and a waste of money to have to pull out the network and reinstall it in a few years because the cabling doesn’t have the required bandwidth.

Category 7 cabling is in the works.

ABC turns to HF during tropical Cyclone

Super Tropical Cyclone Yasi, a category 5 storm, came ashore this morning between Cairns (pronounced Cans) and Townsville, Queensland around midnight Thursday (9 am Wednesday, NY time).

Radio Australia carried Australian Broadcasting Company (ABC) Queensland coverage of the storm, which was extraordinary. Spot coverage, emergency information, sheltering information, updates, and calls from listeners in the midst of the storm. Some of it is pretty intense. One fellow, John, out in the country all by himself in the height of the storm sounded somewhat forlorn, I hope he makes it.

Due to the size of the storm, widespread power outages are expected and may last for weeks or months. As a part of this, there are numerous outages and potential outages in their AM and FM broadcasting chain. To that end, ABC has two shortwave frequencies available for their Queensland service; daytime (8 am to 8:30 pm local time, 2100 – 0830 GMT) on 9710 KHz and night time (8:30 pm to 8 am local, 0830 – 2100 GMT) is 6080 KHz.

Once again, HF (shortwave) radio gets the job done when local stations, cell towers, and internet connections to dead. Sometimes it is the low-tech answer.