Transmitters and Analog Power

@=study this item carefully for quiz

@A.  WVCP has two Harris broadcast transmitters.  The new transmitter, now on air daily, is a Model ZX2000.  We put it into service in 2011.  It is a hybrid transmitter, capable of sending both analog and digital/HD signals.  Our backup transmitter is an analog Harris Quest model. It was purchased in 2000.  Both are solid state transmitters with no tubes.  Power amplification is done through power modules with banks of transistors.   

@B.  WVCP, like most FM stations, uses the indirect method for calculation of power output.  The transmitter readings you take are multiplied into the Indirect Formula and the amount of watts transmitted can be figured.

C.  Indirect Method:  The transmitter’s final amplifier voltage is multiplied by the final amplifier current. This answer is then multiplied by the efficiency factor of the transmitter (F). The antenna gain and transmission line loss are then figured in to determine the amount of watts effective radiated power (ERP) that is being broadcast.  WVCP's ERP is 1,006 watts.

E.  The actual amount of analog power coming out of the transmitter (TPO) is 840 watts.    Because the transmission line is not 100 percent efficient, some power is lost through it.  WVCP's Andrews transmission line efficiency is 85.56%.  The antenna gain then raises the output to determine the final ERP. 

F.  840 watts TPO  X   .8556 =   718.70 watts          

G.  The gain of WVCP's antenna is 1.4.        

H.  718.70   X  1.4  = 1006 watts effective radiated power.

I.  In the days of old we had 1000 watts ERP.  But now the FCC allows us to round up to the nearest 10 watts on the 840 TPO---so that makes the ERP is 1006.

@J.  The power output reading you get from the remote control (channel 02) is a reading in percentage.  To have a legal power output, FM stations must operate between 90 and 105 percent of the power specified in their license.

@K.  WVCP's legal output range is 905 to 1,056 watts ERP, or 90 to 105%.

L.    That's roughly 756 to 882 watts TPO analog.

@M.  You are required to raise or lower the transmitter power or contact the general manager any time the power output exceeds 105, or is less than 90%.

Digital Power: 

N.  When you take transmitter readings you are reading the analog power.  The digital power level is set in the transmitter to be a percentage of the analog power.

O.  As a measure to prevent interference to other surrounding stations, the FCC requires a station’s digital/HD power level to be somewhat less than the effect of the station’s analog signal. Therefore the digital signal will be cleaner than the analog signal, but won’t travel as far as the analog signal. A station’s HD-1 signal and analog FM signal always carry the same programming.  That allows HD radios to “blend” back to the analog signal if you drive out of range of the HD-1 signal.

P.  There is no blending for HD-2, HD-3, or HD-4 FM stations.  These stations perform the way digital television signals do.  You either get a perfect signal or no signal at all.

Q.  All FM radio stations can add a digital HD component to their analog signal without special licensing from the FCC.  However, they must notify the FCC within ten days of starting to broadcast a hybrid (analog and digital) carrier wave(s) on their assigned frequency.

@R.  Any FM radio station can go on their air with an amount of HD power that will result in their digital signal being -14db in strength (volume) below their analog carrier.  If you can prove to the FCC that it won’t cause undue interference to another station, you are allowed to run a greater HD power level that results in -10db.

@S. WVCP is a station that is authorized to operate with an HD power level of -14 db. 

WVCP’s HD/digital TPO (transmitter power output) is 34 watts.  WVCP’s HD/digital  signal emits an ERP (effective radiated power) of 40 watts.     

T.  Transmitter Readings

Revised: 7-19-11

Be sure to read the transmitter during first and last half hours of your show.  This insures that you won’t go over the FCC’s 3 hour rule on observing the station’s readings for proper, legal, operation.

1.  Dial 9-452-7166

2.  When modem answers and says “Enter” put in security code:

1,2,3,4,5,6,7,8, being careful to not make any mistakes.*

3.  Enter: 05,  System response: Channel 05, 0513--or similar numbers—Drop zero and put decimal before last number.  0513=51.3 volts.  Write 51.3 in 05 column of log.

4.  Enter: 04,  System response: Channel 04, 0428—or similar numbers—Drop zero and put decimal before last number. 

           0428= 42.8 amps.  Write 42.8 in 04 column of log.

5.  Enter: 02,  System response:  Channel 02, 0100—or similar numbers—Drop first zero if ending of number is 100 or greater.  0100= 100%.  Write 100 in 02 column of log.  If response is: 0097, drop first two zeros and write 97 in 02 column of log.

6.  Provided that 02 reading is between 90 and 105% you are finished.  Press 99 to turn off remote control unit and then hang up phone.  (See below if percentage is not between 90 and 105%.)

*If you make a mistake with the security code, enter 99, hang up phone and immediately call again to start over with readings.

Harris ZX Transmitter          _____ Harris Quest Transmitter

Code              Function                        Code        _____ Function

00              Temperature                       00                  Temperature

05              Power Amp Volts                01                 Power Amp Volts

04              Power Amp Current           03                 Power Amp Current

02              Power Out Percent            06                 Power Out Percent

07              Reflected Power                 08                Reflected Power

99              Hang Up Modem                  99                Hang Up Modem

02              Raise/Lower Output %      03               Raise/Lower Output %

05               Carrier On or Off                 02                Carrier On or Off

Harris ZX (New) Transmitter

1.  Raise Power Output:   66, 02# ---hold pound five seconds,

Press 02 to read output.  You may need to repeat procedure.

2.  Lower Power Output:  66, 02*  ---hold star five seconds,

Press 02 to read output.  You may need to repeat procedure.

Harris Quest (Standby) Transmitter

3.  Raise Power Output:  66, 03#---hold pound five seconds.

4.  Lower Power Output: 66, 03*---hold star five seconds.

5. Contact the general manager any time you cannot keep transmitter power output between 90 and 105 percent. 

6.  Operators should NOT attempt to turn on the Quest transmitter in the event of a failure of the normal ZX transmitter.  There is a series of steps that must be completed at the transmitter shack to turn on the backup transmitter.  Contact the station manager or chief engineer in the event of a transmitter failure.  Their phone numbers are at the front of this document and in the Control Room Operations Manual.