May 2017
M T W T F S S
« Apr    
1234567
891011121314
15161718192021
22232425262728
293031  

Archives

Categories

Undersea Cable Map

With the advent of fiber optic cables starting in the 1980’s,  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 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 weights about 7 pounds per foot, which is pretty hefty.

There are a couple of interactive maps on line 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 over layed with a downloadable KML file:

Undersea cable map

Undersea cable map

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

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:

Trace Route, Guam

Trace Route, Guam

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

Remotes using a Smart Phone

I was fooling around with my HTC  Android phone yesterday and discovered something that has a definite use for radio remotes.  An Application called Hertz will record .wav files, which can then be transfered via e-mail or ftp to the studio and played back on the air.  The program is pretty slick, it allows sample rates from 8 to 44.1 khz.

I made a sample recording, the microphone in the HTC phone is okay, a better microphone would sound better.  After it was done, I emailed it to myself and listened on the laptop.  The email took about 4 minutes for a 20 seconds of a 32 kHz .wav file.  One could cut that down by choosing a lower sample rate.  I have found that 32 kHz it the minimal acceptable sample rate for analog FM.  Anything lower than that sounds choppy.

In another potential use, a news reporter could use this to record audio to save and transfer to a computer using a USB cable.  The recording time limit depends on the size of the SIM card and the sample rate.  Additionally, my HTC Android phone will detect and use WiFi networks, where available, for data services.  Using a WiFi network will avoid those 3G data charges and also increase download/upload speeds.

My Verizon plan has unlimited data transfer, so it really doesn’t matter what sample rate I use, your mileage may vary.

Couple the Hertz app with the VNC app mentioned previously, and a person could do all sorts of things remotely with a radio station.  The Hertz app is available for free download from the Android app store.

Fireworks sychronized to music played over the radio!

In previous years, I have had the very pleasurable experience of setting up a fire works show remote with music synchronized to our FM radio station.  Ordinarily I don’t go near a remote broadcast, however, this is one of the more intricate broadcasts requiring coordination between the studio, the remote site and the fire works barge anchored 300 yards off shore, out in the Hudson River.  The fireworks company, Garden State Fireworks, are consummate professionals and produce a very well choreographed show.

Giving them the synchronizing track on site is not very hard, however, I was surprised to hear that not every radio station does that.  In fact, one of our, ah, ehm, Clear Channel competitors from The big Metropolitan Center Nearby could not be bothered to do it for the 4th of July fireworks this summer and last summer too.

The synchronizing track is on the left channel of a CD that Garden State Fireworks created, it is 1200 baud FSK data, 8,N,1, so it is pretty robust.

I thought I would post on how I do it and why. First of all, for the how part, there are two options:

  1. Play the music CD at the remote site and relay broadcast quality music back to the studio without any time delay.  Hard to do even with an ISDN line.
  2. Play the music CD at the studio and relay telephone quality audio for the firing track to the remote site from the studio.  Have the remote site play the air signal over the local PA system.

Option number 2 is technically far easier than option number 1, although it takes a fair bit of coordination.  Also, the sound reinforcement guy didn’t like the air signal idea because the quality of the audio.   That is a little nit picky, especially given the fact that much of the music at the fireworks show will be drowned out by the fireworks explosions.    In the end, he saw it my way.

Here is a list of equipment needed:

  1. Telco auto answer coupler, such as the Indy Audio
  2. Telco Hybrid, such as the Telos
  3. If the announcer is at the fireworks site, a POTS CODEC such as a Comrex Matrix or blue box
  4. Wireless microphone
  5. Telephone set and cord with RJ-11 connector
  6. Miscellaneous mic cables, power cords, etc
  7. At the remote site, two pots lines from the local phone company, long distance  service as required.

Here is the block diagram:

Note, this assumes no delay in the telco network, which under ordinary circumstances using wired, not cellular network, there should not be any.  The touchiest part of the whole thing is getting the stage coordinated with the studio during the transition to the remote broadcast.  Once that is done, everything else just falls into place.

The firing computer is located on shore next to our broadcast booth.  They send the signal out to the barge on a wireless LAN link.

That is the how part.  Here is the why (soundtrack is a little low):

That is from three years ago, but you get idea.

Even though I don’t work for these people anymore, I asked if they needed help with the broadcast this year.  “Nope, we got it, thanks.”  I will be paying close attention.

Yeah, there is an app for that

In the never ending evolution of remote broadcasting equipment, Comrex has yet another way to connect to the studio with broadcast quality audio.  For use with their Comrex Bric-link or ACCESS equipment, they have authorized an iPhone app called Media5.   It requires a SIP account and costs $4.99 to download, which last time I checked, was pretty reasonable.  I am not surprised that remote equipment manufactures have tapped into the 3G/4G wireless networks that span most of the country.

Time was when a remote required ordering an equalized phone line from Ma Bell.  This usually required 2-4 weeks, depending on the local branch.  Spontaneous remotes were but a pipe dream.  Then came Marti with inexpensive RPU transmitters and receivers, this greatly reduced the lead time required for establishing remote broadcasts.  The downside to Marti equipment is it takes at least some technical know how to set up because of all the antennas and coax and such.

Comrex came on the market with Telephone Line frequency extenders then with 3 line comrex units (3XP/3XR).  A three line unit split the incoming audio into three different sections, reducing each to 300 to 3,400 Hz telco line base band.  At the other end, the answering unit changed the sections back to their original frequency range, then recombined them into pretty good sounding audio from 50 to 10,000 Hz or so.  I have used these units on several occasions.  I believe that one of the stations I work for still has one of these in their storage unit, along with several EFTs.

Latter, Comrex came out with POTS line codecs like the Hotline, Matrix and Blue box.  Now only one phone line was needed to do a remote. This greatly simplified remote availability and set up.  The downside to these is it had to be straight dial tone, no PBX’s or any thing like that.  A noisy line can create problems with audio quality and dropouts.

The Matrix can be used with ISDN and they used to have a GSM module to use with certain cellular networks.

The latest Comrex products include IP and VOIP capabilities.  These systems are great when a broadband WIFI networks is available to be used.  Unfortunately, an open WIFI with good signal strength is not always at hand.  So the 3G/4G option is a natural.

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!