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E-skip, tropospheric ducting and other VHF propagation phenomena

While the FM frequency band (88 to 108 mHz) is mostly line of sight, there are things that cause long distance reception hundreds or sometimes even thousands of miles from the transmitter.  For a radio engineer, this can lead to all sorts of problems.  Some serious like STL cut outs, and some quite funny, such as the general manager panicking when several new stations suddenly pop up in town.  One of the many jobs of a broadcast engineer is to avoid problems and fix them if they show up (preferably the former).

Tropospheric Ducting prediction map

Tropospheric Ducting prediction map

The first and most common of these phenomena is Tropospheric ducting.  This happens in warmer weather when there is a high pressure system nearby and is more prevalent over flat terrain.  What happens is a warmer layer forms in the atmosphere above a cool layer.  That is why it is also known as “temperature inversion.”  This causes a higher refractive index, which means that normally the signal would carry on out into space, however, upon encountering this warm layer it is bent back to earth.   It can last a few minutes to several hours. It effects all frequencies but is most prevalent above 100 mHz.

In some more sever cases, FM stations can travel 500 or more miles and override the local station’s transmitter site 15 miles away.  In the age of digital STL’s, co-channel and adjacent channel interference can cause the STL receiver to unlock and mute.  Analog STL’s will become hissy or drop out altogether.  It can be a big problem.

Unfortunately, not a lot can be done about main channel interference.  It will go away eventually, and no, the station causing the interference is not operating illegally or any other thing.  One consolation, if the duct is open in one direction, it is also open in the other, so say hello to all your new temporary listeners in East Podunk.

As far as STL paths go, the best defense is to have a good strong signal at the receive site.  Boosting the signal with a preamp at the back of the STL receiver will not do anything.  Larger, higher gain antennas at the transmit and receive will help, more transmitter power will help.  Sometimes diversity receive antennas will help because at the 950 frequencies 100 feet or so of altitude may make all the difference.  Other than that, things like a backup RPU path using a lower frequency, a backup T-1, a backup ISDN line, a Comrex Matrix, basically anything to restore programming.

There is a tropospheric ducting prediction site called Worldwide Tropospheric Ducting Forecasts.  They produce daily maps and predictions based on weather patterns.

Night and Day layers of the Ionosphere

Night and Day layers of the Ionosphere

The next propagation type known to abnormally affect VHF frequencies is called Sporadic E or E skip.  This happens went ionized particles appear in the E layer of the ionosphere and it is more prevalent during the high period of the sun spot cycle when the atmosphere is unsettled due to solar storms.  It is more likely to affect frequencies below 125 mHz, so main channel interference may be noted, but STL’s and other broadcast auxiliary services will not likely see any effects.

This can happen anytime of the year in any terrain and in any weather condition although it seems to be more prevalent in summer and for some unknown reason, around Christmas.

Ionospheric propagation is also known as skywave and is responsible for long distance communications in the MF (AM broadcast band) and HF (Shortwave broadcast band).

During sunlit periods, the Ionosphere breaks down into several layers; the D layer, which is responsible for absorption of AM signals during the daytime.  The E layer, which normally reflects signals less than 10 MHz.  The F1 and F2 layers, which primarily effect HF and lower VHF, from 10 – 40 MHz or so.

During sporadic E events, the E layer becomes heavily ionized in specific small thin areas, sometimes called clouds.  This can last a few minutes or up to several hours.  The effect is normally more pronounced with lower frequencies.

In this internet age, there is, of course, a website that can predict or at least define sporadic E, DXMaps.com has maps similar to the tropospheric ducting maps above.

Ionospheric Map

Ionospheric propagation map

Occasionally, solar storms will effect communications on all frequencies. The last time I heard this was in the last sun spot peak around 2000 or so. I was listening to the radio and all the stations faded for several seconds. It turns out a huge solar flare had erupted and send a stream of particles through the Earth’s atmosphere.  I happened to be driving down the road and immediately my cell phone started ringing.  Listening to the panicked program director on the other end, you’dve thought the earth has stopped spinning on it’s axis.  Anyway, it does happen once in a while.

Proper termination of long audio wire runs

This is standard telephone company stuff, however, it would seem that several radio engineers have forgotten this.  I was reading on one forum where an AM station was using 1000 feet of 12 gauge romex to send audio from the studio to the transmitter out back.  The owner was complaining that the audio sounded bad.

Longer wire runs need to be terminated with the characteristic impedance of the cable being used, normally 110 ohms or so for typical audio wire.  This is because impedance mismatches can cause return loss just like in an RF circuit.  Exactly what the effect of the mismatched impedance depends on the length and frequencies involved.  On shorter cable runs of less than 100 feet or so, this usually is not an issue.

The result of return loss is part of the audio energy gets reflected back to is origin (a standing wave), where it mixes with newer audio.  This can cause out of phase issues and usually the result is high tinny sounding audio with distortion in the mid range frequencies.  In other words, it ain’t pretty.  This can really become an issue with digital audio because of the higher bandwidth requirements for high sample rates.  It has always struck me as odd that AES/EBU audio uses XLR type connectors.  An XLR connector does not maintain the characteristic 110 ohm impedance of most digital cable and itself can cause pretty significant return loss. But anyway…

There are a number of options for proper termination:

1.  Transformers are often used to match the impedances of circuits. A transformer converts alternating current at one voltage to the same waveform at another voltage. The power input to the transformer and output from the transformer is the same (except for losses). The side with the lower voltage is at low impedance, because this has the lower number of turns, and the side with the higher voltage is at a higher impedance as it has more turns in its coil.  Western Electric 111C audio transformers were often used in equalized TELCO circuits sending audio over long distances on copper pairs.

WE 111 repeat coil, one of the best such transformers ever made

WE 111 repeat coil, one of the best such transformers ever made

2. Resistive network impedance matches such as H or T or L pads are the simplest to implement. They limit the power deliberately, and are used to transfer low-power signals, such as unamplified audio or radio frequency signals. Almost all digital circuits use resistive impedance matching which is usually built into the structure of the switching element.

H pad impedance matching network

H pad impedance matching network

3.  Active balanced converters using opamps with high input impedances (10 Kohm bridging resistance) that first greatly reduce the voltage, then amplify it are often used an audio circuits.  They have the advantage of active gain control and are often used in conjunction with gain reduction and limiting circuits.

Unbalanced to balanced audio converter

Unbalanced to balanced audio converter

The above diagram shows an active unbalanced to balanced audio converter.  The advantages of such a circuit are active gain controls can be added to set levels.  With additional feedback circuit elements, it can also be used for automatic gain control, gain reduction, limiting and so forth.

For most inter and intra studio wiring, professional audio equipment is designed for 0 dBm 600 ohm balanced audio (AKA line level audio).   Audio cable such as Belden 8451 or like multi-pair cables terminated on punch blocks or connectors works well.  Cable impedances and matching are generally not a design consideration.  Long cable runs, longer than 150 feet or so, do need to be terminated in a high quality audio installation.

Studio Builds, the never ending cycle

The lease is up, its time to move! Yay, we get to rip apart the old place and redo it! Again! It seems to be a matter of course that every few years a radio station will move. Such is the case with WKZE in Red Hook (the town, not the area in Brooklyn). Their lease is up on the “Grotto” location, so the owner has decided to move to a new location, closer to the center of town.

The new location was the former thrift shop.  I know this because while I am working there, a constant stream of older people stop by and tell so.  Once, while working alone doing some pre-move work punching down wires and computer network cables, I had to use the facilities.  There I sit, on my porcelain throne, when I hear, “Hello?” in and old shakey voice.  A quick glance at the door reveals it is not locked.  Oh, NOs!  Okay, don’t say anything, she’ll go away.

“Hello?”

“Hello?”

“Hello, is any body here?”

“Hello?  Very strange, the doors are open but nobody is here.  Hello?”

Oh for the love of Pete, “I’m in the bathroom,” I finally said.

“Where is the bathroom?” said the interloper.

I refused to say anything else and she finally left.  She could have taken all my tools, if she wanted to.

Anyway, the studios themselves are pretty simple, one production studio and one air studio.  A T-1 line to the transmitter site, which turned out the be the hardest thing about the entire operation.  We moved the old Radio System consoles rather than purchasing new equipment.  Radio Systems has a program called a Millennium upgrade, where you buy a new control surface, which replaces all moving parts, for something like $2,300.00 or so.  For that, basically, a new console is had.

Radio Systems Former RS-12 now Millennium 12 console

Radio Systems Former RS-12 now Millennium 12 console

The new production room is long and narrow.

WKZE new production room

WKZE new production room

The air studio is large and spacious.  They often have live music from this studio, which is really cool.  The station uses Prophet Systems automation equipment, although it is live most of the time.

WKZE air studio before furniture is installed

WKZE air studio before furniture is installed

The main office area is one large room where desks will be located.

WKZE office, painted no furniture yet

WKZE office, painted no furniture yet

We are moving in stages:

  1. Prep work, installing all the computer network cable, phone system cable, pulling all the audio and control wiring.  Then the contractor finished up the drywalling and painting.  Nice Colors!
  2. Ordering phone lines and T-1 line.  Ahhh, the phone company, such a pleasure to deal with, we had to pull a new cable through the underground conduit from the street to the building because the old cable did not have enough pairs.  The conduit length is about 75 feet or so.
  3. Removed the old production room console and took it to the shop to rebuild.  It was not that difficult really, although a little cumbersome.  I throughly cleaned out all the dust dirt and other detreious materials from the console frame and install the new control surface.  I also checked all the power supply voltages with an oscilliscope to make sure there was no ripple.  The original consoles were made in 1992, not bad for an 18 year old board.
  4. Built a new production room with the rebuilt board.
  5. Tested all computer jacks, audio wiring, etc prior to move.
  6. Move T-1 circuit and all office and studio telco lines to the new location.  Fortunately, the phone company is a local company not the big V we have in other cities.  They were able to work with us and get things paralleled to the new location, something a large company might not have understood.
  7. On the air from the production room at the new location
  8. Remove the main rack, intact and move it to new location
  9. Remove office phone system and install at new location
  10. Remove and rebuild old air studio console
  11. Install rebuilt air studio console in new studio, wire
  12. Transfer operation to new studio

Right now, we are on step #6.  That is going to be done next Tuesday (the day after memorial day) morning I believe.  We should have the move completed by the end of the week.  I’ll post updates as they become available.

Should I renew my free subscription to Radio World?

When I left my former place of employment and set out as a contractor, I also left my Radio World subscription behind. After I was let go, or quit or whatever it was, I was thinking that my days in radio were over or at least winding down and I had bigger things to worry about that trade magazine subscriptions.

I have been checking the Radio World web site and find that it gets updated from time to time, usually several weeks behind the magazine.  So the question is, what am I missing?  As one commenter on the radio info board put it, the magazine keeps getting smaller and smaller, soon they’ll have to rename it Radio Pamphlet.

I’d like to stay abreast of things in the technical end of the radio business, but is Radio World the way?  There was a time when it was a technical magazine full of good timely articles well written by fellow engineers.  Occasionally I still find something interesting to read, that is true.  Interspersed with that are lots of advertisements, useless information and many pro HD radio articles.  Is it worth the price?  I don’t know, I am still pondering that one.

Wire terminations

Radio studios involve quite a bit of wiring.  Runs between the console and equipment are pretty straight forward, whatever the connector required for the equipment to whatever the connector required for the console.   When it comes to trunk runs between the rack room and the studio, however, some type of terminating block is required.

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66 block or M block insulation displacement wire termination

This particular cabling installation is for low level signaling, contact closures and the like.  It uses a Belden cable with 37 un-twisted wires which do not follow the standard Western Electric color code.  The color code can be found here.  If it where audio or data, the wires would be terminated differently.  That color code can be found here.  For more information on color codes and pinouts, see this post.

Many engineers use the venerable 66 block or M block insulation displacement termination.  These terminal blocks were designed by ATT to terminate 25 pair 22 through 26 gauge solid wire.  The the original design was rated for category 3 (16 MHz or 10 mb/s) communications standards.  Newer designs are category 5 or 5e compliant (350 MHz or 100 mb/s).  Notice the part about solid wire.  Most audio wire is stranded and as such, the metal fingers on a 66 block will cause stranded wire to spread out loosing contact with the terminating finger.  This causes intermittent connections and audio dropouts, which I have experienced often (before I knew better, I used 66 blocks when building studios).  The way to cure audio dropouts on a 66 block is to heat the termination fingers with a soldering iron.  This melts the wire insulation and gets it out of the way.  In the long run, it is better to use more suitable terminations.

Krone LSA-PLUS 110 type wire termination block

Krone LSA-PLUS 110 type wire termination block

The 110 block is updated version of punch block for high speed networks.  it is also designed for 22 through 26 gauge solid wire.  This is the termination used on category 5, 5e, 6 patch panels and RJ-45 jacks.  They are also formed into block type terminations the size of small 66 blocks.  The 110 block is designed for 500 MHz (1 gb/s) or greater bandwidth.  Krone makes a version of a 110 block called LSA-PLUS which is an acronym that stands for: Lötfrei, Schraubfrei, Abisolierfrei, Preiswert, Leicht zu handhaben, Universell anwendbar, Sicher und schnell.  Which translates to: no solder, no use of screws, no insulation removal, cost effective, easy to use, universal application, secure and fast.  Unlike a standard 110 block, the Krone block is designed for solid or stranded wire.  110 blocks are acceptable for use with AES/EBU digital audio at sample rates greater than 268 KHz as well as gigabit networks and analog audio.

In very old installations, I have seen christmas trees.  This is a wire wrap system where wires are wrapped around metal fingers that form the shape of a pine tree, hence the name.  They were very popular in the fifties and sixties and only work with solid wire.  It is also time consuming work and requires special tools and skills.  Wire wrapping is a bit of a lost art.

Christmas Tree wire wrap termination block

Christmas Tree wire wrap termination block

Screw barrier strips have been used to terminate audio cables from time to time.  I wouldn’t consider this method because it is too time consuming, takes up too much space and is difficult to label.

ADC ICON wire termination block

ADC ICON wire termination block

ADC makes a good termination block called ICON (Integrated Cable Organization Network) which uses QCP (Quick Connect Panel) connectors.  the connectors are small square devices that are insulation displacement termination (like 66 and 110 blocks) but require a special tool to “punch down.”   This particular type connector is well suited for stranded wire from 22 through 26 AWG.  QCP connectors are also used on some of ADC’s patch panels and other audio products.  Like any other termination technology, they are only as good as the person punching down the wires.  QCP connections are small high density devices, I have seen them get mangled by a someone in a hurry who got his punch down tool across two of the terminals by accident. ICON blocks can be used for digital audio, however, they do not maintain the 110 ohms impedance of most digital type audio cables (neither do XLR connectors, by the way).  This can lead to some return loss, which on longer cable runs can cause problems.

Radio Systems Studio Hub wiring diagram

Radio Systems Studio Hub wiring diagram

Radio systems prefers RJ-45 connectors with Category 5 cable, something they call Studio Hub.  These are 110 blocks as noted above, but designed primarily for computer networks.  Radio Systems discovered that the impedance of most audio cable is very close to that of computer network cable, audio cable is designed for 110 ohm impedance vs. computer network cable which is designed for 100 ohm impedance.  Therefore, RJ-45 connectors and shielded or unshieled twisted pair work well with balanced professional audio, either analog or digital.

For analog audio wires, ICON blocks seem to be the best, most secure high density termination system.  In all my years of using them, I have never had a connection go bad.  110 block and other category 5 or 5e systems also work well.  For digital audio, Krone blocks or 110 blocks need to be used in order to maintain the full bandwidth characteristics of the cable being used.  Using in appropriate cable and or terminations in digital audio circuits often leads to impedance mismatches and high return losses in the system.

Radio Ships

Radio London air studio aboard the MV Galaxy

Radio London air studio aboard the MV Galaxy

These were broadcast platforms that were usually anchored in international waters broadcasting popular music to several European Countries including Great Britain, Holland, France and Spain in the late 1960’s through late 1980’s.  The reasons for these peculiar operations was strict government control of all broadcast outlets and programming in those particular countries. The BBC was known to be stodgy and repressive of new music, particularly rock music from bands like the Rolling Stones, the Beatles, the Who, the Kinks, and others.

At the time, there was no specific law preventing ships anchored in international waters from broadcasting to shore based listeners, a loophole in the government control was found and exploited.  That loophole has been closed in most places, so as they say, don’t try this at home.

At one time there were several ships out there in the English Channel and coastal Denmark. The first and best known of these was Radio London or “The Big L.” It broadcast on 1133 KHz from December 16, 1964 to August 14, 1967 using a 50,000 watt RCA ampliphase transmitter. The ship itself was the M/V (motor vessel) Gallaxy, a converted WWII minesweaper formerly known as the USS Density.  After Radio London went off the air, the ship was transfered from port to port until it ended up in Kiel, Germany, were it was finally scrapped in the late 1990’s.

Radio Caroline was the main offshore competitor, broadcasting on 1520 KHz and several other frequencies off and on from 1964 until 1990 or so using several different vessels to transmit from.

MV Galaxy with radio mast

MV Galaxy with radio mast

One incident in off shore broadcasting that has always fascinated me was the burning of the Mebo II, then transmitting Radio Northsea International off the coast of Holland (this ship moved around quite a bit) in 1971. Later investigations revealed that the staff of an offshore competitor, Radio Veronica, was responsible for the firing of the ship.  Apparently, in those days the competition was brutal.

I like the nice calm music with the increasingly frantic DJ (West, no East). In any case, the ship remained afloat and returned to the air the next day.  The final European offshore broadcaster was something called Laser 558 on M/V Communicator.  It broadcast using to CSI 25 KW AM transmitters on 558 KHz in 1983, again, off and on for several years until 2004.  The CSI grounded grid transmitters may have been inexpensive to purchase, but I’ll bet they cost a lot to run.  This would be especially true if one were using diesel generators as the main electrical power provider.  As a result, they were usually run at about 1/2 power.  Eventually, M/V Communicator ended up beached in the Orkney Islands off of Scotland.

The only such attempt in the US was Alan Wiener’s MV Sarah, known as “Radio Newyork International” anchored off of Jones Beach on 1620 KHz.  The owner’s figured 4 miles off shore was far enough to be in international waters, the FCC felt otherwise, I believe at the time, 12 miles was (and still is) the territorial limits for the US.  Four miles was not international waters, as the broadcasters claimed.  These guys were arrested and sent to trial.  After several years all charges were dropped.

Anyway, an interesting bit of radio history. Goes to show the lengths that some will go to when feeling repressed.

What is really wrong with EAS?

Aside from it hasn’t worked… Over the last several, the FCC has released no fewer than five proceedings regarding EAS.  To date, few, if any meaningful changes have taken effect.  The stated purpose of the Emergency Alert System (EAS) is to:

  1. provide the communications capability to the President to address the American public during a national emergency.
  2. may be used by state and local authorities to deliver important emergency information, such as AMBER alerts and weather information targeted to specific areas.

Seems pretty straight forward.  Local weather emergencies would seem to be the most likely reason for EAS activation, followed by things like Amber Alert, chemical spills, evacuations, etc. To meet those ends, the FCC mandates that radio (traditional and IBOC), television, cable, wireless cable, direct satellite TV, and satellite radio participate in some way or another.  So far, it seems like a fair idea.  Then comes the implementation, which is flawed. To start with, EAS still relies on a daisy chain relay system designed during the 1960’s for CONELRAD.  The over the air monitor assignments of other broadcast stations are the only mandatory information sources in the system.  Other, more relative local sources such as the national weather service, local government and so forth are optional. Next, the most used and most useful part of the EAS, local and state level alerts are completely optional.  Very little or no information is provided to local government agencies on how to access EAS in the event of an emergency.  Then the issue becomes one of un-maned stations.  The initial EAS message goes out over the airwaves, which takes about 2 minutes at most, then it’s back to the music.  No amplifying information, check back for more information when it becomes available, etc.  Nothing.  It has occurred in several cases where a radio show is voice tracked, complete with a weather forecast, which is the opposite of real time weather warnings.  If one happens to miss the initial EAS broadcast because they were listening to another station or whatever, well, too bad. Finally, the National Weather Service itself over activates.  One line of summer time thunderstorms passing through the area can trigger 10 or even 20 EAS alerts.  Over activating, with the same digital tones (rrrrrrannk, rrrrrrank, rrrrrank) followed by the EBS tone then some computer generated voice just gets annoying. To summarize:

  1. The national EAS has never been tested, who knows if it will work
  2. The EAS relies on unreliable over the air daisy chain relays for it’s mandatory monitor assignments
  3. Local and State level EAS (including weather related alerts, something that could be really useful) is optional
  4. When connected to the NOAA weather radio system, the NWS over uses the EAS activations

Here is an idea:  For at least ten years now, the idea of a CAP has been batted around.   It seems like a good idea, lets do that.  Get rid of EAS, send emergency information to everyone’s cellphones or whatever and stop fining broadcasters for missing a monthly test.  The weak link in the EAS is the broadcaster’s themselves.  History has shown (over and over again) that the current crop of radio station owners cannot be bothered to meet even the simplest of their public obligations.  The FCC has shown it is only interested in collecting big fines for a missed EAS tests, not actually making the system work.  The system is broken.  As terrestrial radio (and TV) goes terminal, the public will still needs to receive emergency information, the CAP idea can fill this requirement. It is time to pull the plug on EAS once and for all.

Computer file manipulator

It just doesn’t have the same ring as Disk Jockey or DJ.  However, that would be an apt description of the person who plays the hits on most radio stations these days.

It is mostly just drag and drop the next element into the play deck, if anything needs to be done at all.

Technics SP-15 Turntable

Technics SP-15 Turntable

I remember when DJ’s actually jockeyed disks, it was a sight to behold.  Back in the day when everything was on vinyl except the commercials, which were on cart, the DJ had his or her hands full.  Most of the songs where in the 2:30 to 3 minute range, so while the song was playing, the next song had to be cued up on the platter, the old song needed to be put back into it’s sleeve and shelved (most of the time), check the log to see what was on deck, pull the next commercial stop set, answer the phone and god forbid if the Program Director called on the hot line and it rang more than 3 times.  And hopefully the head wasn’t too far away, that coffee went somewhere, after all.  While all that is going on, timing, audience interaction, hitting the post and sounding fun.  In spite of what Howard Stern says, it was not easy.

Today, of course, if there is even a person in the studio, they may glance up at the computer screen every now and then to see when the next time they need to talk.  Otherwise, they would be engaged in talking on the phone with their girl friend, texting, surfing the internet, or watching the baseball game on TV.

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!