Power Increase

HD Radio™ Technology – Power Increase

Definition

The FCC is presently allowing most FM stations to increase their digital power. Refer to the following FCC document: http://fjallfoss.fcc.gov/edocs_public/attachmatch/DA-10-208A1.pdf. This document explains that the FCC will:

  • Permit most FM stations to immediately increase total digital power by 6 dB, a four-fold power increase
  • Limit power increases for stations currently licensed in excess of class maximums, i.e., “super-powered” stations, to protect analog radio service from interference
  • Establish application procedures for power increases up to 10 dB
  • Establish interference remediation procedures that require the Media Bureau to resolve each bona fide dispute or impose tiered power reductions within 90 days

It is suggested that stations take advantage of whatever power increase is possible without exceeding the NRSC-5-C out-of-band emissions mask for HD Radio broadcast operations.

The table below shows the different terminology involved with the various levels of power increases. Please note that -20dBc is the reference power level of the digital signal compared to the analog signal.

 

Total Digital/Analog

Power Ratio (dBc)

dB Increase

Power Multiplier

Total Digital/Analog

Power Ratio (linear)

-20

0

0

1/100

-18.5

1.5dB

1.4

 

-18

2dB

1.6

 

-17

3dB

2

1/50

-15

5dB

3

 

-14

6dB

4

1/25

-13

7dB

5

 

-10

10dB

10

1/10

 

Implementation

There are several ways to increase your digital power depending on your existing equipment setup and capabilities. Consider these principles when implementing the digital power increase:

If you are using a separate digital antenna and transmitter:

  • Increase the power output of the digital transmitter (if there is enough ‘headroom’ to allow this increase). Be aware that the transmission line and/or antenna my need to be upgraded to handle the additional power.
  • If space is available on the tower, you may increase the number of antenna bays to increase the antenna gain factor.

If you are low-power combining analog and digital using one transmitter:

  • Increase the digital Exciter/Exgine drive power (may require re-optimizing amplifier bias).

If you are high-power combining analog and digital using separate transmitters:

  • A new digital transmitter may be needed. Be mindful that this method may necessitate upgrades to the electrical service and building cooling systems and may require a higher power dummy load.
  • Asymmetric sideband technology can also be employed to independently adjust sideband levels in order to maximize sideband power for a given protection ratio. This feature will be integrated in iBiquity’s Broadcast Software Release Version 4.4. This feature has not yet been approved by the FCC; however, stations may begin to implement it under a test authorization from the FCC.
  • For asymmetric sidebands, the power level of one of the sidebands can be increased. Neither sideband shall be reduced in power below the nominal level.