Engineering Radio – Page 83 – One Hundred percent Human Generated Content for your Reading Enjoyment

Three generations of emergency communications

Even before CONELRAD was introduced in 1951, radio broadcasting was a critical part of the emergency communications infrastructure. The government recognized early on the ability of radio to transmit data and information quickly, over large areas to the general public. It works when all other systems fail, as demonstrated repeatedly over the years, the last of which occurred during Hurricane Sandy last October. Massive destruction from flooding in lower Manhattan and shoreside Brooklyn rendered the electrical grid, telephone network, cellular network, and the internet out of order. Fortunately, enough radio stations stayed on the air and people used battery-powered AM and FM receivers to obtain information.

CONELRAD poster, circa 1950's — CONELRAD poster, circa 1950’s

CONELRAD served two purposes; first, radio stations either re-tuned their transmitters to 640 or 1240 KHz or switched off the air. Then, each station that was still on the air would transmit for ten minutes, after which, they turned off and the next station in the chain would turn on and transmit for ten minutes. This was designed to confuse the Soviet bombers flying over the north pole on their way to incinerate us. Secondly, the CONELRAD stations were to distribute emergency information during and after the said attack.

Recently, I found this CONELRAD receiver in a bomb shelter at a radio station. It dates to pre-1963, which is when CONELRAD was replaced by EBS.

EBS or the Emergency Broadcast System was a refinement of CONELRAD in several areas. EBS used a two-tone attention signal to unmute receivers and alert the public that something important may be happening. Initially designed as a national system to warn of an impending attack, in later years it was also used by state and local governments to warn of other emergencies like weather, etc.

The current system is EAS or Emergency Alert System.

The Emergency Alert System was an advancement of the EBS in several areas. Using SAME protocol in the message headers allowed stations to automate alert message relays. This was driven by the desire for unattended operation. The use of SAME also allowed many different types of messages to be filtered by alert type and area. Each EAS unit also had an internal voice recorder. All of this was upgraded in 2011 with the introduction of CAP, which would take email messages and generate computer voice alerts to be sent out over broadcast stations.

Three generations of emergency communications equipment found at one facility.

The main problem with EAS CAP is it violates the engineering principle of KISS (Keep It Simple, Stupid). It is an overly complicated system that relies on the internet, e-mail servers, the public telephone system, and other infrastructure that may not survive natural or man-made disasters, enemy attacks, or other disruptions. Even something as simple as a national test proved to be problematic in 2011.

For a real emergency information network, the idea of WGU-20 has some merit. Two or more well-positioned medium to high-powered LF stations could serve as a PEP distribution network and reliably cover the entire country. With such a system, every broadcast station, cable head end, and NOAA radio transmitter could monitor the LF stations directly, thus replacing most of the over-the-air daisy chain and or FEMA leased lines. The advantages of LF is that it is fairly immune to HEMP, it goes a long way reliably, can have multiple redundant transmitter sites located within secure areas like military bases, and uses time-proven technology. That would be a real, cold war solution. But no, let us instead rely on a hodge podge of ISPs, TELCO leased lines, 3/4G wireless networks, SMS, satellite links, e-mail servers, and the like, because: Hey! It’s the digital age, we don’t need none of that stinking broadcasting crap.

The Nautel XR6 AM transmitter

I’ve been away working in Burlington, VT (WVMT, 620 KHz, Burlington) for the last coupla, installing this nifty Nautel transmitter:

Nautel XL6 transmitter, WVMT Burlington, VT — Nautel XR6 transmitter, WVMT Burlington, VT

I like the Nautel units, both AM and FM; they are well-designed, well-built, rugged transmitters. I have lost track of how many of these units we service in the field, partly because they are becoming pretty much standard equipment at all of our installations.

Continental 315R-1 AM transmitter, WVMT, Burlington, VT

The transmitter it is replacing is a Continental 315R-1, which is based on the Collins Power Rock design. It is a PWM transmitter with a 15,000 volt power supply. In their day, these were not terrible transmitters, however, like their Harris MW-5/10/50 PDM brethren, frequent thorough cleaning is required to keep the dirt/dust from arcing over. Unfortunately, it is becoming more and more difficult to obtain parts for these units. This transmitter was installed in October of 1983, thus, almost thirty years of service is quite enough. This unit we did not cut up and scrap, rather, it is sitting by the back door, waiting for any takers.

Continental 315R1 modulator/RF sections — Continental 315R-1 modulator/RF sections

The interior of the Continental 315-R1 transmitter. Modulator section is on the left, RF section is on the right.

The good news is, WVMT is another one of those “successful AM station” stories. You know, the kind of station that has local programming, local sports, news, community presence and most importantly, makes money. For all those diligently studying the “AM Problem” for the up and coming NAB conference this April, here is a clue: It’s the programming…

Nautel XR6 transmitter, wvmt Burlington, VT — Nautel XR6 transmitter, WVMT Burlington, VT

This is the Nautel XR-6 on the air. Positive peaks, anyone?

We turned that down a little bit. Also, the station does not run AM stereo, the AM stereo mod monitor is simply a usable relic of a bygone era.

WVMT is noted as the first radio station licensed to the state of Vermont, signing on on May 10, 1922. It has a three tower directional array located down in the swamp. For some idea of perspective, it is 1,150 feet (350 meters) from the transmitter building to the center tower, the towers are 411 feet (125 meters) tall spaced 405 feet (123 meters) apart.

WVMT three tower directional antenna array, Burlington, VT — WVMT three-tower directional antenna array, Burlington, VT

WVMT antenna system from back of transmitter/studio building. That is a long walk over rough terrain in the middle of the night or anytime really, but especially in the middle of the night.

Undersea Cable Map

With the advent of fiber optic cables starting in the 1980s, the majority (one estimate says 99%) of this country’s overseas communications are carried by undersea cables. These are interesting system constructions, being first redundant and second, self-healing. Glass fiber stands themselves are fairly fragile. Bundling several together and then sinking them in the ocean can create mixed results. Deep ocean bottoms are often very rugged, containing mountains, canyons, and fault lines. Thus the submarine cables used have to be pretty rugged.

There is a common misconception that fiber optic cables do not need repeaters. That is not true, while they do not need as many repeaters as copper cable, repeaters are still required approximately every 40-90 miles (70-150 km) depending on the cable type. These active devices are another failure point. Overall, it is a complex system.

Submarine Fiber Optic Cable cross section — Submarine Fiber Optic Cable cross-section, courtesy of Wikipedia

Cross-section of a submarine fiber optic communications cable:

1. Polyethylene
2. Mylar tape
3. Stranded metal (steel) wires
4. Aluminum water barrier
5. Polycarbonate
6. Copper or aluminum tube
7. Petroleum jelly
8. Optical fibers

It weighs about 7 pounds per foot, which is pretty hefty.

There are a couple of interactive maps online that have detailed information about where these cables go, date in service, and data capacity. My favorite is Greg’s Cable Map which is a Google map with cable data overlayed with a downloadable KML file:

This shows a new cable called the “Emerald Express” which is going into service in 2013. Throughput is reported as 60 Tbps, which is moving right along. As noted on the map, this is more of a schematic diagram connecting two shore side points. The path the cable takes is an estimate and the actual geographical location may (is likely to) be different. Click on any line on the map for cable information. Most cables have their own web page and Wikipedia article.

Another undersea cable map is the Telegeography Submarine Cable Map, which has many of the same features noted above:

China US submarine Cable network diagram

Just in case you were wondering, as I often do, how a TCP/IP connection is being routed to any given place. For fun, I tried a trace route to a known server on Guam and found the results interesting:

Approximately 231 ms round trip route from NYC to LA to Guam and back, which is over 8,000 miles (12,850 km). A few of the intermediate routers did not answer and I tried this several different times; the same routers time out. This missing information looks to be small steps, not large ones. So, which cable goes directly from LA to Guam? Possibly the China-US Cable Network (CHUS) (picture above). At 2.2 Tbps and landing at San Luis Obispo, that is the likely candidate for the cable that carried my data.

As a general exercise, it is kind of fun, although it may be harder to figure out a particular route to say London or Berlin because there are many more different possibilities.

Route latency is something to keep in mind when planing out AOIP connections for remotes and other interactive type connections between studio and remote location. Almost nothing is worse than that half second delay when trying to take phone calls or banter back and forth with the traffic reporter.

h/t: jf

Restoration work on an RCA transmitter

I read through this article about the ongoing restoration work of an RCA SSB T-3 transmitter and found it interesting. The RCA T-3 transmitter is a 20 KW SSB/ISB HF (2-28 MHz) unit designed for point-to-point telephony service. Because SSB requires class A or AB low distortion amplifiers, this is a large unit, even for its age and power levels.

From the looks of the before pictures, this transmitter was in sorry shape.

Here is a brief video of the transmitter start-up:

These units were designed to be switched on and run at 100% duty cycle for most of their operating lives. That is some heavy iron there. This particular unit was made in 1959. More here and video part 2:

Anyway, before geosynchronous satellites, HF point-to-point transmitters were used to make long-distance phone call connections and send data and pictures back and forth over long distances. Out in Hicksville, Long Island, Press Wireless ran a data and fax system that used HF for long-haul data transmission. Much of the WWII reporting from Europe and the Pacific Theaters was carried over this system.

Text would be printed out on a mechanical teletype machine at something like 60 words per minute, which was considered fast for the time:

Tuning across the band, one can often hear Radio Teletype (RTTY or RATT) which uses a 5-bit Baudot code, 170 Hz shift with 2125 HZ representing a Mark or 1 bit and 2295 Hz representing a Space or 0 bit, which is a bit different from the Bell 103 modem specifications. This is what it sounds like at 75 Baud:

So slow you can almost copy that by hand.

The RCA H (SSB T-3) unit above was independent sideband (ISB), which means that either sideband or both could be modulated independently of the other, thus two channels of information could be transmitted. SSB bandwidth is about 2.7 KHz, which is good for telephone-grade audio or low-speed data.

I sort of wish I was living in California again, I’d lend a hand.