LPFM stations are permitted to install and operate HD Radio. HD Radio permits stations to broadcast in digital quality, add up to 3 “sub channels” for different programming as well as send album art and titles to compatible receivers. This is in addition to continuing to provide an analog signal receivable on all FM radios.
Facility considerations
In order to set up HD Radio, you will need to make sure that your studio/audio chain can handle the additional subchannels if you deploy them. If you do run subchannels, you must make sure that your EAS can interrupt all of the subchannels during alerts.
Because of transmitter power limitations in the GatesAir FAX150 certified transmitter, you may want to make sure that you are running an antenna that does not exhibit loss. For example, a one bay circular polarized antenna like the Nicom BKG-77 or Shively 6812B may experience over 3 dB of loss. For an HD operation, you should make sure that you have at least a 2 bay circularly polarized antenna. For the Nicom BKG-77, space the two bays at 0.85 wave ((300 / frequency MHz) x 0.85 = meters) for best gain opportunities. LPFM stations not contending with a second adjacent waiver can use a gain vertical antenna like the Norwalk Dominator.
Equipment
There are currently two companies making transmission equipment for HD Radio, Nautel and GatesAir.
Please note that transmitters operating in the HD hybrid mode have lower transmitter power output (TPO) ratings than the transmitter would have operating in the analog only mode. Because of these lower maximum TPOs, a multi-bay antenna and low-loss feedline may be needed to achieve the station's authorized effective radiated power (ERP). See the chart below to determine the maximum TPO available with each model.
Nautel
As of March 1, 2021, the VS-300LP equipped with the VS-HD is now FCC certified. HD is not available for the Nautel VX series (VX-300). If you purchase Nautel and have ambitions to go HD, get the VS-300LP to be HD ready.
GatesAir
The Flexiva series transmitters (FAX150, FAX300 & FAX500) are FCC certified and can be adapted to HD. HD is achieved by adding an additional board inside of the transmitter. You will also need an importer/exporter, the Flexiva FMXi 4g in order to bring in your multicast programming.
Maximum Transmitter Power Output for HD transmitter models
| Model | Analog only | Hybrid -20 dBc | Hybrid -14 dBc | Hybrid -10 dBc |
|---|---|---|---|---|
| Nautel VS-300LP + VS-HD | 330 | 290 | 180 | 120 |
| GatesAir Flexiva FAX150 | 165 | 120 | 105 | 80 |
| GatesAir Flexiva FAX300 | 330 | 330 | 300 | 160 |
| GatesAir Flexiva FAX500 | 550 | 550 | 400 | 300 |
Power/Coverage
The actual maximum power of the digital carrier is based on a percentage of the authorized ERP for your LPFM station. That percentage is based on whether protection to a first-adjacent channel facility is required. To determine this, we do a contour study based on an interfering contour of the LPFM station and the service contour of the other station. Taking the nearby first-adjacent channels into consideration, this is the chart for how much power an LPFM can run based on the class maximum of 100 watts ERP. If your station’s ERP is lower due to height above average terrain, these numbers will have to be adjusted:
Symmetric Operation
This is the most common form of digital operation where the same digital ERP is used on both the lower and upper sidebands. Based on where the LPFM interfering contours reach the affected first adjacent channel stations, you will use the lower of those values on both the lower and upper side bands. (For example, if the 50.7 dBu interfering contour overlaps the 60 dBu contour of the first adjacent channel station on the lower sideband, but the 49.6 dBu interfering contour does not overlap the 60 dBu contour of the first adjacent channel staiton on the upper sideband, you will still be limited to -13 dBc.)
| Interfering F(50,10) contour of the LPFM that reaches the 60 dBu contour of the other first-adjacent channel station | Operation allowed at x decibels below carrier (dBc) | Digital can be % of analog power | Digital power for maximum class (100w) LPFM station |
| 51.2 dBu or above | -14 dBc | 4% | 4 watts |
| 50.7 dBu~51.1 dBu | -13 dBc | 5% | 5 watts |
| 50.3 dBu~50.6 dBu | -12 dBc | 6.3% | 6.3 watts |
| 49.6 dBu~50.2 dBu | -11 dBc | 7.9% | 7.9 watts |
| 49.5 dBu or less | -10 dBc | 10% | 10 watts |
Asymmetric Operation
This involves operating at different digital ERPs on the lower and upper sidebands. This option can be used in cases where the LPFM station is too close to a first-adjacent channel station. In this case, we don't use the worst of the two, but instead, each sideband is treated independently.
New rules have been adopted for asymmetric operation on May 23, 2025. FM broadcast stations (including LPFM), except for those on 107.1~107.9 (channels 296~300) can deploy asymmetric operation without an experimental authorization. The top 5 channels cannot be done at this time due to concerns by the aviation industry regarding interference to navigation aids above 108 MHz. Stations on 107.1~107.9 seeking asymmetric operation may request authorization through an experimental permit.
| Interfering F(50,10) contour of the LPFM that reaches the 60 dBu contour of the other first-adjacent channel station | Operation allowed at x decibels below carrier (dBc) | Digital can be % of analog power | Digital power for maximum class (100w) LPFM station |
| 51.2 dBu or above | -17 dBc | 2% | 2 watts |
| 50.7 dBu~51.1 dBu | -16 dBc | 2.5% | 2.5 watts |
| 50.3 dBu~50.6 dBu | -15 dBc | 3.2% | 3.2 watts |
| 49.6 dBu~50.2 dBu | -14 dBc | 4% | 4 watts |
| 49.5 dBu or less | -13 dBc | 5% | 5 watts |
NOTE: Class B and B1 stations in the commercial band, despite having larger service contours, will still be “protected” at the 60 dBu contour.
Don’t let these low powers fool you, a digital signal does travel a little differently than an analog signal. Even at the maximum -10 dBc, the digital signal may not replicate your full analog service area, but it will perform better than 10 watts analog. LPFM stations operating with foothill effect conditions (higher elevation/lower HAAT) will probably fare the best, but may also be prone to more first-adjacent channel issues.
The 2010 Order in MB Docket 99-325 outlines the policies related to the remediation of interference from a station operating HD to the analog signal of a first-adjacent channel station of any class.
Multicasting
When broadcasting in HD, your station is sending a digital bitstream. That bitstream can be divided up among your multicast channels. The bandwidth can be configured where you have better audio quality on HD1 and HD2 with a lower quality on HD3 and HD4. The fewer multicast channels the station has, the better the quality can be distributed among those channels.
Your HD1 channel MUST match the programming on the analog channel.
LPFM and NCE stations must keep ALL multicast channels noncommercial in nature. The rumors you may have heard that LPFM/NCE stations can run commercials on HD2 are not true.
LPFM stations with a commonly-owned FM translator or FM booster are required to broadcast the analog program on the translator or booster(s). FM translators and boosters may also operate in HD and in those cases, the multicast (HD2~HD4) streams may be carried on their respective multicast streams on the translator/booster.
HD multicast channels must be identified at the top of the hour like the analog channel. IDs on the digital channels (including HD1) need to not just include the call letters (including the -LP for LPFM) and the city, but also some kind of an acknowledgement of the digital service. Some legal ID examples include:
- WREC-LP HD1 Riverton
- WREC-LP and WREC-LP-HD1 Riverton
- WREC-LP Digital HD1 Riverton
- WREC-LP 102.7 HD1 Riverton
- WREC-LP HD2 Riverton
All multicast channels must be connected to EAS in the audio chain and must forward alerts pursuant to the FCC rules regarding national alerts and in accordance to the state EAS plan.
Costs to convert
HD is not cheap. For the equipment, budget at least $30K for the HD equipment and ancillary devices. Also, as we mentioned, you may need to rethink your antenna due to the transmitter power output limitations on combined FM/HD transmitters.
For noncommercial radio (full-service and LPFM), Xperi (formerly iBiquity) charges a one time licensing fee of $5,000. This license fee can be paid at $2,000 up front and then $500 annually until paid off. Noncommercial stations do not have to pay any additional fees based on revenues and the noncommercial license covers all multicast streams. You must have a license with Xperi before you can take delivery of HD equipment.
FCC filings required
An LPFM station can turn on HD without advance permission from the FCC. Once HD has been activated, the station is required to file a Digital Notification with the FCC. This form is NOT available through LMS for LPFM stations. A paper form must be emailed. Please contact REC Networks for assistance.
FCC decisions
MB Docket 99-325: Report and Order 17 FCC Rcd. 19990. (Declares that in-band, on channel to be the sole digital technology permitted on FM/AM broadcast stations. Permits interim IBOC operations)
MB Docket 99-325: Multicast Operations 20 FCC Rcd. 5136. (Permits experimental multicast operations.)
MB Docket 99-325: Second Report and Order 22 FCC Rcd. 10344 (Permits regular use of IBOC digital broadcasting, LPFM specifically permitted at paragraphis 56-58, establishes technical rules.)
MB Docket 99-325: Third Order 25 FCC Rcd. 1182 (Permits power increases for digital sidebands with first-adjacent protections as described above).
MB Docket 22-405: First Order 39 FCC Rcd. 11251 (Permits the use of asymmetric power levels without an experimental permit on channels 201~295). Adopted September 25, 2024; rules effective May 23, 2025.
More information
Please review the websites of the various stakeholders:
- Xperi – HDRadio.com (General information about HD radio for broadcasters and listeners.)
- Nautel
- GatesAir (formerly Harris)
REC can help with your Digital Notification and to determine if the LPFM station can operate at increased digital power. LPFM licensees can get more information on HD digital power for their station through the myLPFM.com portal.
LPFM stations operating HD Radio
(As of September 24, 2024)
- KXRN-LP Laguna Beach, CA
- KBUU-LP Malibu, CA
- KVCB-LP Vacaville, CA
- WMXR-LP Miami, FL
- WGVV-LP Rock Island, IL
- WZRF-LP Wilmington, NC
- KMGG-LP Albuquerque, NM
- WDFC-LP Greensboro, NC
The HD Hijack Effect
LPFM and full-service stations that are not running HD have reported that those with HD radio receivers are hearing the signal of a distant FM station on the same channel and that station just happens to be broadcasting in HD, even if the listener is very close to the desired FM station. This is because the HD signal is "wider" as the digital sidebands located on each side of the analog carrier. Secondary stations, such as LPFM and FM translators that are not operating HD are more vulnerable as they are more likely to be inside the interfering contour of the distant station.
Short of disabling HD Radio on the receiver, there is nothing that can be done, other than adding HD on your station. Never call the other station to report this to them. There's no method for LPFM stations to remediate this through the FCC. This is the general nature of secondary service.
Updated May 26, 2025 to reflect the change in the rules regarding asymmetric operation. Also added information on the maximum TPO of transmitter models. Also added information on HD Hijack.
