5.122
5.123 Additional allocation: in Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia, South Africa, Zambia and Zimbabwe, the frequency band 3 900-3 950 kHz is also allocated to the broadcasting service on a primary basis, subject to agreement obtained under No. 9.21. (WRC 19)
5.125
US340 The band 2-30 MHz is available on a non-interference basis to Federal and non-Federal maritime and aeronautical stations for the purposes of measuring the quality of reception on radio channels. See 47 CFR 87.149 for the list of protected frequencies and bands within this frequency range. Actual communications shall be limited to those frequencies specifically allocated to the maritime mobile and aeronautical mobile services.

Wiki entries

Access Broadband over Power Line (Access BPL)

Current Use 3.5–4.65 MHz Access BPL

According to the FCC's definition, Access BPL is "a carrier current system installed and operated on an electric utility service as an unintentional radiator that sends radio frequency energy on frequencies between 1.705 MHz and 80 MHz over medium voltage lines or over low voltage lines to provide broadband communications and is located on the supply side of the utility service’s points of interconnection with customer premises. Access BPL does not include power line carrier systems as defined in § 15.3(t) or In-House BPL as defined in § 15.3(gg)."

Low voltage lines are defined as lines carrying, for example, 240/120 volts from a distribution transformer to a customer's premises. Medium voltage lines carry between 1,000 and 40,000 volts from a power substation to neighborhoods, and may be overhead or underground.

Access BPL is an unlicensed service operated under Subpart G of Part 15 of the FCC's rules. Radiated emission limits from medium voltage lines in the 1.705-30 MHz range must not exceed the limits in 47 CFR 15.209, and those from 30-80 MHz must not exceed the limits in 15.109(b). Systems that operate on low voltage lines must comply with 15.109(a) limits across the entire 1.705-80 MHz range.

When Access BPL systems must use notch filters to protect licensed services, the notch must be at least 25 dB below applicable Part 15 limits in the 1.705-30 MHz band, and at least 10 dB below the limits in the 30-80 MHz band.

There are 12 sub-bands in which Access BPL systems are not allowed to operate anywhere to protect aeronautical (land) stations and aircraft receivers. Those excluded bands are listed in 15.615(f), and are excluded in the list of Access BPL bands in this entry.

Access BPL systems are not allowed to operate within the sub-band 2173.5-2190.5 kHz within 1 km of coast station facilities listed in 47 CFR 15.615(f)(2)(i), to protect the internationally-recognized standard maritime calling frequency of 2182 kHz.

No Access BPL emissions are allowed in the 73.0-74.6 MHz radio astronomy band on overhead medium voltage lines within 65 km of the Very Large Array radio telescope in New Mexico (34 04 43.5N, 107 37 03.82W), or within 47 km of the VLA on underground power lines or overhead low voltage lines.

Access BPL operators must consult at least 30 days in advance when deploying systems near various FCC field offices, aeronautical and maritime stations, radar systems, radio astronomy stations, and research areas. Details are in 47 CFR 15.615(f)(3).

Amateur Radio 80 m Band

Current Use 3.5–4 MHz Amateur Radio 80 m Band (ITU Region 2)

According to the ITU, "this band is used for contacts over distances of up to 500 km during the day, and for distances of 2 000 km and more at night. It is heavily used during communications emergencies."

Sometimes the upper portion of this band, which is mostly used for SSB communications, is referred to as 75 m, while the lower portion, used for CW and narrowband digital modes, is referred to as 80 m.

In the U.S., the ARRL has adopted the following band plan. The plan may apply in other countries as well. Following the band plan are the band segments that are authorized for the specified U.S. licensee classes.

ARRL BAND PLAN:

Frequency (kHz)	Use
3590	RTTY/Data DX
3570-3600	RTTY/Data
3790-3800	DX window
3845	SSTV
3885	AM calling frequency

Band Uses Authorized for AMATEUR EXTRA Class Licensees:

Range (kHz)	Authorized Use(s)
3500-3600	RTTY and data
3600-4000	Phone and image

Band Uses Authorized for ADVANCED Class Licensees:

Range (kHz)	Authorized Use(s)
3525-3600	RTTY and data
3700-4000	Phone and image

Band Uses Authorized for GENERAL Class Licensees:

Range (kHz)	Authorized Use(s)
3525-3600	RTTY and data
3800-4000	Phone and image

Band Uses Authorized for TECHNICIAN and NOVICE Class Licensees (200 W MAX):

Range (kHz)	Authorized Use(s)
3525-3600	CW only

Shortwave Broadcasting

Current Use 3.9–4 MHz 75 m band (shared with North American 80 m amateur radio band)

Various bands throughout the HF (and, technically, the MF) spectrum are used for what is commonly referred to as shortwave broadcasting. Most broadcasts use AM modulation, which can be received on inexpensive shortwave receivers. Within these bands, shortwave broadcasters use channels spaced every 5 kHz. Different broadcasters may use the same channel at different times, and schedules of shortwave broadcasts (which are coordinated through the International Telecommunication Union) change on a regular basis. Most shortwave broadcasts also use very high power, as much as 500,000 W, using very large antenna arrays.

Because many broadcasts are sent through relay stations, the identity of the broadcaster does not necessarily tell you where the signal is coming from. For example, Radio Moscow is retransmitted from a relay station in Cuba, to provide a strong signal into North, Central, and South America.

Most shortwave bands are referred to by their approximate wavelength. For example, the 9400-9900 kHz band is referred to as the "31 meter band," because the wavelength is approximately 31 m.

The Website Short-Wave.info (linked below) can be used to identify shortwave stations broadcasting on specific frequencies at specific times, in a specified language.