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RADIO BROADCAST DATA SYSTEM (RBDS)

Radio Broadcast Data System (RBDS) is a communications standard that embeds small amounts of digital data into regular FM broadcasts. It may also be known as Radio Data System (RDS).  On many of the newer FM broadcast receivers found in vehicles use you will see scrolling text on the screen.  

A local example is talk station WOKV-FM on 104.5 MHz.  Stations may give their station identity nickname, title, and artist.  The data sent is inaudible to the listener.  FM broadcast audio limits are up to 15 kHz, the stereo pilot is 19 kHz, plus a 38 kHz stereo difference signal. Subcarrier Authorization (SCA) transmissions may be also present on 42 kHz and/or 67 kHz.

SCA is used for background music which has very low fidelity.  Muzak in Jacksonville in the past used WQIK’s 67 kHz. SCA channel.  It is not currently being used since Muzak is on satellite now and has numerous channels.  WJCT-FM has used their SCA for their reading service.  

RBDS uses a 57 kHz subcarrier which is the third harmonic of the 19 kHz stereo pilot.  57 kHz subcarrier was selected to minimize interference and intermodulation interference from stereo pilot and stereo difference signal. The data is sent with error correction. 1     You may see a question of forward data correction on the Extra Class Amateur exam. 2

The following fields can be contained in RDS/ RBDS:

AF--Alternative Frequencies. It allows a receiver to retune to another frequency of the same station if the first signal become too weak when moving out of range.

CT--Clock Time synchronizes a receiver clock.

EON--Enhanced Other Networks allows the receiver to monitor other networks for traffic programming.

PI--Program ID is determined by applying a formula to the station call in the US.

PS--Program Service. Call letters, station identity.  Can be stored in the stations presets.

PTY--Program TYpe. News, Rock, etc.

RT--allows the station to transmit a 64 character text or syncs programming details such as title and artist.

TA, TP--for Traffic Announcements and Traffic Programming. Can stop a CD and increase volume to listen to traffic information.

TMC--Traffic Message Channel. Digitally encoded traffic information for automotive navigation systems.  The data is encrypted and a decoder, possibly using a subscription service, would be required.

More expensive car stereos will have TMC, RT and or PTY.  Home systems will have PS, RT and PTY.

RDS is being proposed in California for use with time based pricing of electricity.  RDS chipsets are manufactured by ST Microelectronics, Silicon Labs, and NXP.  viaRadio of Melbourne, FL manufactures HEARO local alert receivers.   It can provide local NOAA radio alerts in text form.

Palm Bay, FL and Indialantic, FL uses HEARO to alert people of emergencies.   Leon County Schools in Tallahassee, FL and 
Brevard County Schools use HEARO in schools for lock downs weather emergencies.  The University of Central Florida uses HEARO to distribute emergency alerts to campus personnel.  Montserrat Island in the Caribbean uses HEARO alert residents of volcanic activity.  3 

There is an abundance of detailed information on the Internet on how this system works and its uses.

Footnotes:
1.       RDS, Wikipedia

2.       ARRL, Extra Class License Manual

3.       RDS, Wikipedia


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Tall Broadcast Antennas and GoPro Videos

In the United States a tower is an antenna structure attached to the ground and a mast is a vertical antenna support mounted on some other structure such as a building or other antenna structure.  Masts and towers are often used interchangeably.  The materials used may be steel lattice, tubular steel, reinforced concrete, fiberglass, and even wood.  

Shorter masts can be galvanized steel poles and are often referred to as monopoles.  Sometimes cellphone towers are disguised as trees, church towers, flag poles, power line towers, and water towers.  These are known as stealth towers.

Masts are used as radiators for long and medium wave broadcasting. These will have insulators on the base. Telescopic masts and tilt over and non- tilt towers are commonly used for amateur service and pump up masts are used for remote television and radio broadcasts. Balloons and kites have been used to carry up an antenna wire such as used for Radio Marti and Field Day.  

A guyed mast is cheaper to build than a self-supporting tower.  Sometimes towers will have bunches of aluminum streamers to attract static electricity to the tower rather than the radiator.

Antenna access for riggers known as “tower dogs” may be accessed by ladder, and service elevators.  1

There are excellent YouTube videos made with GoPro helmet cameras on tower maintenance. 2, 3, 4, 5, 6.    

Watching these up close on a tablet or IPad may make you feel dizzy.  Some people have a fear of heights. Television’s Dr. Phil says that our brains do not develop a full sense of fear until a person reaches their late twenties.  7  

Car insurance recognize this and rates are usually higher until one reaches twenty five.  These videos show they are using safety harnesses and doing free climbing only when necessary.  These professionals appear be noticing for changes in wind, weather (especially lightning).  

Hard hats and a climbing buddy is present as well as ground personnel.  Since it is a long way down some of them carry up to thirty pounds of tools and replacement parts and lights.  Falling tower ice is a lethal problem in northern climates.

I thought I did not have a fear of heights until I climbed an old fifty foot windmill tower.  As I looked down I noticed that the swimming pool down below was getting smaller and I wondered just how strong the bolts were that supported the tower and wished that I had on safety equipment.  I recalled the Bell System slogan that says to the affect there is no service so important, no service so urgent, that it cannot be done safely.  Lesson learned:  use a safety harness.

Proper lighting must be considered.  Ruggedized under-run incandescent bulbs to maximize bulb life, LED’s and strobe lights are used. 1  

If a tower requiring lighting is not painted, strobe lights are used and must flash 24 hours a day.  There is usually a high brightness mode for use in daylight and a lower brightness mode for twilight and night time.  Running the strobes at full brightness at night would also light up the ground area under the tower and be a lighting nuisance.

The tallest antenna tower in Florida is WFLA TV in Riverview, FL (Hillsborough County) at 1400 Ft tall.  3

On US 301 between Starke and Ocala there is an unusual location of a tower that is mounted in a hole that is about twenty feet below average terrain.  Perhaps they wanted it to have a bedrock base for support.

References:
1         Wikipedia, Radio Masts and Towers

2         YouTube: Stairway to Safety, climbing a 1700 foot tall tower to change a light bulb     

3         YouTube: WFLA TV Tower      

4         YouTube: Tower Climbers working at 1700 feet  

5         YouTube: Ride up  and down 1700 ‘ tower

6         YouTube: Climbing the stick 

7         CBS Television, Dr.  Phil

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