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Federal Government fixed/mobile
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The bands 32-33 MHz, 34-35 MHz, 36-37 MHz, 38-39 MHz, and 40-42 MHz are for federal agency and Army, Navy, Marine, and Air Force fixed and mobile use, supporting training, test range operations, research and development, and search and rescue.
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Frequency Bands |
| Band | Use | Service | Table |
| 32 - 33 MHz | - | - | F |
| 34 - 35 MHz | - | - | F |
| 36 - 37 MHz | - | - | F |
| 38 - 39 MHz | - | - | F |
| 40 - 42 MHz | - | - | F |
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Radio Astronomy (38 MHz)
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The bands 37.5-38 (secondary) and 38-38.25 MHz (primary) are allocated to the radio astronomy service in the United States and in other parts of the world. This frequency range is considered low frequency (long wavelength) for radio astronomy, since it is not much above the ionospheric cut-off frequency, which is typically in the ~5-30 MHz range, depending on solar activity. In the United States, these bands are shared with active (transmitting) services.
Radio astronomy observing in this band is challenging since radio frequency interference may propagate from a long distance away and ruin observations being obtained with very sensitive radio telescopes. The Long Wavelength Array (LWA), located on the site of the Very Large Array radio telescope near Socorro, New Mexico, is one of the few major instruments that uses this band.
At these frequencies, the Sun, the Milky Way galaxy, and a few supernova remnants are among the very brightest sources in the sky.
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Frequency Bands |
| Band | Use | Service | Table |
| 37.5 - 38.25 MHz | Low Frequency Radio Astronomy | Radio Astronomy | - |
External Links:
Associated Files:
An image of the sky at a frequency of 37.9 MHz, obtained by the Long Wavelength Array (LWA).
Each image shows the full sky, down to the horizon at the image's edge. Depending on the current operating mode of the LWA's Prototype All-Sky Imager experiment, there may be one or two images. If there is one, it shows the total intensity — the power coming from each point on the sky. If there are two, the left will show the total intensity, and the right will show the intensity of circularly polarized radio waves.
At the upper left you can see the average time of the data that went into the image (given in UTC, which is basically the same as Greenwich Mean Time). There is no time gap between the images: we are imaging sky in real time with a 100% duty cycle. At the upper right is the central frequency of the image. In the center is a 100 kHz bandwidth spectrum from a single antenna and polarization; the images are produced from the middle 75 kHz.
Finally, we've labeled the brightest objects in the sky:
Cas A — a supernova remnant
Vir A — a supergiant elliptical galaxy also known as M87
Tau A — the Crab Nebula, a supernova remnant
Cyg A — a bright radio galaxy
Jup — Jupiter, which only can be seen when it is bursting
Sun — the Sun, which can become so bright that it wipes out everything else in the image!
Dashed line — the plane of our galaxy
GC — the center of our galaxy
Of course, there will sometimes be points in our image other than these labeled ones! Most of these are due to radio frequency interference (RFI): radio emissions from sources other than the sky. The sky will sometimes be wiped out by bright RFI, particularly at low frequencies and during the day. However, some blips just may be something new: flares from Hot Jupiters or magnetars; radio counterparts to gamma-ray bursts; or something totally new and unexpected. Our computers will be monitoring these movies to let us know when something unusual pops up!
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Access Broadband over Power Line (Access BPL)
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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).
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