Marcus WA2DCI’s Commercial Radio Facts

From the Desk of Joe AC2ND:

Last night I attended the Suffolk County Amateur Radio Club meeting.  The guest speaker was the Chief Engineer for WALK, 97.5.  He gave a presentation on  AM and FM broadcast radios.  Here are some interesting facts:

WA2DCI Programming His Repeater


1)      The FM HD broadcast sub signal from WALK uses 200 watts.  The standard FM broadcast is 50,000 ERP.  The range is the same for HD and standard FM despite the power differences.

2)      AM broadcast shapes its radiation pattern of the antennas by the number of towers and location of the towers.  Some stations feed the towers at different  phases to affect the pattern (similar to this .  All towers are “hot” as they are the driven elements, unlike Ham direction antennas that used elements on the antenna as driven, parasitic.

3)      Broadcast antennas radiate horizontally as well as vertically since table top radios and dipoles are used at home receivers while cars and portables use vertical antennas.

4)      The FM signal standard was derived in the 1960’s.  It combines both mono signal AND stereo since people at the time had many mono FM sets.  Instead of establishing an entirely different band for the Stereo signals, the signals were combined.  Quality suffered because of this.  From this experience, the FCC learned its lesson about sacrificing quality.  The new HD TV signal  use an entirely new band and optimize the signal for quality.

5)      The FM broadcast radio stereo signal is double side band without a carrier.  To maintain quality stereo without the typical side band distortion, a Pilot signal is used on the signal, and “replaces” the carrier.  On this same FM broadcast signal, an RDS channel is provided for text information. Two more edge siganla exist on the FM signal that are used for HD radio.  HD 1 must be the same as the stereo signal by FCC regulations, but HD 2 can be another program.

6)      HD talk signals can encode up to 6 channels on the same FM broadcast frequency since audio only has a narrow bandwidth.  Music can only fit two HD sub-channels.

7)      There are four classes of FM broadcast transmitters.  Class A is <= 6 kw ERP.  Class B is <= 50 kw.  Class C is > 50kw.  Class D is <= 10 w on the 88 to 92 Mhz band (for campus radio stations at schools and colleges).  WALK is a Class B, one on the only ones on Long Island, with all others running Class A or D.  With the exception of one station, all the Class C 50kw and higher stations are west of the Mississippi River, where they need to cover more territory to get to people, cows and coyotes.  If a  tower is over 300 ft., the ERP has to be reduced as the tower increases in height.

8)      There is no requirement any longer for the operator of a radio station to have an FCC license.  The burden falls on the station to have trained and qualified operators (part of the federal government deregulation effort).

9)      All programming is now handled via computers.  No tape decks, turntables or mixer boards any more.  Any mixer board is really an interface to a computer, much like a joystick to a game console.  Radio stations typically have redundant servers the contain three days of programming in advance.  As a back of to both servers failing, the local desktop computer contains a full day of programming (music, ads, editorials, ect…).

10)   Satellite feeds typically are free.  However it is mandatory to also play the commercials embedded in the programming.  A 3 minute window is provided for local ads and commentary.

11)   The a FCC licensed radio station must be participate in the Emergency Broadcast System or turn itself off during a broadcast of the system.  Since the radio station needs to by the equipment to monitor the EBS, all stations rebroadcast EBS messages and none opt out to turning themselves off.

12)   The EBS system uses satellite, radio and internet as three separate paths to activate stations.  Any one of the three will activate a radio station.

13)   The EBS tone at the beginning of the message contains the activation information.  Which may contain information concerning which area of the country, state or counties are being activated.

14)   The EBS has never be activated for a cause, even on 9-11.

15)   The EBS was accidently activated in 1955.  They found that there were problems in the mid-west, but it was never retested.  Only regional tests are conducted.  The most recent being yesterday in 5 Mid-West states.

And you might have thought the broadcast radio was simple.  Marcus, WA2DCI,made a wonderful presentation.


Find out more about Marcus WA2DCI and the WA2DCI Repeater Systems