Radio frequency band
The
80 meter
or
3.5 MHz
band is a span of radio
frequencies
allocated for
amateur
use, from 3.5?4.0
MHz
in North and South America (
IARU
and
ITU Region
2); generally 3.5?3.8 MHz in Europe, Africa, and northern Asia (
Region
1); and 3.5?3.9 MHz in south and east Asia and the eastern Pacific (
Region
3).
[a]
The upper portion of the band, which is usually used for phone (voice), is sometimes referred to as
75 meters
; however, in Europe, "75 m" is used to name an overlapping
shortwave broadcast band
between 3.9?4.0 MHz used by a number of national radio services.
Because high absorption in the
ionosphere
's
Sun
-activated
D layer
persists until nightfall, 80 meters is usually only good for local communications during the day, and hardly ever good for communications over intercontinental distances during daylight hours. But it is the most popular band for regional
communications networks
from the late afternoon through the night time hours.
[
according to whom?
]
At night, 80 m is usually reliable for short- to medium-distance contacts, with average distances ranging from local contacts within 200 miles / 300 km out to a distance of 1,000 miles / 1,600 km or more at night ? even worldwide ? depending on atmospheric and ionospheric conditions.
Overview
[
edit
]
The
nominal
"80 meter" band begins at 3.5
MHz
(85.7 m
wavelength
) and goes up to 4.0 MHz (74.9 m wavelength). The upper part of the band, mostly used for voice, is often referred to as 75 meters, since in Region 2, the wavelengths in that section are between 80?75 meters (adjacent to or overlapping a shortwave broadcast band called by the same name: "75 m").
Natural and human-made noise
[
edit
]
80 meters can be plagued with noise: The same ionospheric refraction that makes long-distance shortwave propagation possible also traps terrestrial noise under the ionosphere, preventing it from dissipating into space, which quiets down radio bands at higher frequencies, above ~20 MHz. The 80 m rural noise floor is mostly determined by noise produced by distant tropical
thunderstorms
and cumulative regional sources of human-made static. The urban and suburban 80 m noise floor is typically set by the amount of noise generated locally, from electrical machinery and household electronics, and is generally 10?20 dB stronger than typical rural noise.
On 80 meters, nearly all areas of the world are subject to weather-induced noise from regionally local thunderstorms, and combined distant lightning strikes from
tropical
thunderstorms that perpetually supply world-wide a continuous source of radio static.
Daytime and nighttime use
[
edit
]
The 80 meter band is favoured for
ragchews
between amateurs within a range of 500 miles / 800 km. During contests the band is filled with activity beginning before sunset and continuing all through the night.
The
ionosphere
's
D layer
significantly affects the 80 meter band by absorbing signals. During the daylight hours, a station in middle or high latitudes using 100 watts and a simple dipole antenna can expect a maximum communication range of 200 miles (320 km), extending to a few thousand miles or more at night.
Global coverage can be routinely achieved at high latitudes during the late fall and winter, by stations using modest power and common antennas. The higher background noise on 80 meters, especially when combined with higher ionospheric absorption, causes transmitting stations with higher effective radiated power to have a decided advantage in being heard by long-distance receiving stations. With very high transmitting antennas or large vertically polarized arrays and full legal power, reliable worldwide communications occurs over nighttime paths. Good receiving antennas have far more modest requirements to reliably get signals from worldwide sources.
Cumbersome large antennas
[
edit
]
Antennas for 3.5 MHz are large: For example, a quarter-wave vertical sized to resonate at 3.6 MHz is approximately 65 feet (20 meters) high; for reasonable antenna efficiency, even a reduced-size antenna needs to be a large fraction
(
?
?2?
/
3
)
of that height, which is still a formidable construction project for an amateur. Erecting such large antennas and ensuring the antennas radiate significant power at low angles are two of the challenges facing amateurs wishing to communicate over long distances. Amateurs interested in regional communication can use low wire antennas, such as horizontal
dipoles
, inverted vee dipole antennas or
loop antennas
on this band. Horizontally polarized antennas closer than a quarter-wave to earth produce predominantly high-angle radiation, which is useful for short-distance propagation modes, such as
near vertical incidence skywave
. Nonetheless, occasional favorable propagation conditions make substantial distances still possible with modest-height antennas.
Mobile radio operation with portable antennas is still possible, but the relatively short length of practical mobile antennas compared to a quarter-wave antenna ? usually under 10 feet (3.0 meters) vs. around 65 feet (20 meters) tall ? results in the need to compensate with a large
inductive loading coil
to bring the antenna to resonance. However a large coil looses power through resistive heating of its wire, and that wire resistance is always high enough to compete for
RF
power against the antenna's meager effective
radiation resistance
: Since short antennas have very low radiation resistance, the lion's share of their fed power is lost to heat, and their efficiency is typically below 10%, with roughly 90% of the power input lost to wire and ground resistance. Additionally, the large inductance of the loading coil creates an antenna system with an extremely narrow bandwidth (very high
Q
), which can be good for reducing received noise, but makes changing frequency a challenge, since one must retune the loading coil's inductance.
History
[
edit
]
| This section
needs expansion
. You can help by
adding to it
.
(
January 2012
)
|
The 80 meter band was made available to amateurs in the United States by the Third National Radio Convention in 1924.
[1]
The band was allocated on a worldwide basis by the International Radiotelegraph Convention in 1927.
[2]
Propagation
[
edit
]
As the
maximum usable frequency
for long-distance communication seldom dips below 3.5
MHz
anywhere on the planet, the main propagation barrier to long-distance communication is heavy
D-layer
absorption during the daytime, ensuring that
DX
paths must be largely, although not entirely, in darkness. At times, there is pronounced dark-side
gray-line propagation
, which is most useful on polar routes, away from equatorial thunderstorm activity.
At higher latitudes, a noticeable
skip zone
sometimes appears on the band during nighttime hours in midwinter, which can be as much as 300 miles / 500 km, rendering communication with closer stations impossible. This is not generally a problem at middle or equatorial latitudes, or for large parts of the year anywhere, but it does occasionally limit local wintertime traffic on the band in areas such as
Northern Europe
, the northern tier of the United States and Canada.
During spring and summer (year-round in the tropics), lightning from distant storms creates significantly higher background noise levels, often becoming an insurmountable obstacle to maintaining normal communications. Nearby
convective weather
activity during the summer months can make the band completely unusable, even for local communications. In the winter months during the peak years of the
sunspot cycle
,
auroral
effects can also render the band useless for hours at a time.
Frequency allocations
[
edit
]
The
International Telecommunication Union
allocated the whole 500
kHz
from 3.5?4.0
MHz
to amateurs in the Americas, and 3.5?3.8 MHz or 3.5?3.9 MHz to amateurs in other parts of the world. However, amateurs outside the Americas must share this useful piece of spectrum with other users, usually on a joint primary basis. As a result, authorities in the affected parts of the world restrict amateur allocations between 3.7 MHz and the top of the band.
Some allocations are as follows:
Country
or
Area
|
ITU
Region
|
Allocation
(in
MHz
)
|
Refs
|
Argentina
[
citation needed
]
|
2
|
3.500?3.750, 3.790?3.800
|
?
|
Australia
[
citation needed
]
|
3
|
3.500?3.700, 3.776?3.800
|
[b]
|
Canada
|
2
|
3.500?4.000
|
[3]
|
Europe
|
1
|
3.500?3.800
|
[4]
|
India
|
3
|
3.500?3.700, 3.890?3.900
|
[5]
|
Japan
|
3
|
3.500?3.580, 3.599?3.612,
3.662?3.687, 3.702?3.716,
3.745?3.770, 3.791?3.805
|
[6]
|
Korea
|
3
|
3.500?3.550, 3.790?3.800
|
[c]
[7]
|
New Zealand
|
3
|
3.500?3.900
|
[5]
|
Russia
|
1
|
3.500?3.800
|
[4]
|
United States
|
2
|
3.500?4.000
|
[8]
[9]
|
Lower band edge
[
edit
]
As is common for many other wide amateur bands, the lower edge of 80 meters is predominantly used for
radio telegraphy
(called
"CW"
), with the lower 10
kHz
(3.5?3.51
MHz
) primarily used for long-distance communications. It is common for illegal marine operations, generally using
USB
voice ("phone"), to occupy frequencies on the low end of 80 meters. Most intrusions of this type are from fishing vessels and their marker buoys; although most of those vessels are from SE Asia and South American ports, some band intrusions are committed by fishing vessels based in ports in the USA and Canada.
Upper band edge
[
edit
]
For Canadian and U.S. Amateurs with infeasibly perfect transmitters, the highest usable frequency in the 80 m band for
lower side band
voice ("phone") would be 3.999
MHz
. But depending on quality and condition of radio, audio characteristics, and proper adjustments the bulk of emissions on lower sideband will typically occupy 3.9970?3.9997 MHz. All
SSB
transceivers have third- and fifth-order products of significant level, typically only 30?35 dB below PEP for third order intermodulation. This means any operation above 3.998 MHz even
lower sideband
(LSB) comes with some risk of illegal emissions, even with good equipment.
It is a common misconception that operating a transmitter set at 3.9997 MHz is not legal, since emissions extend beyond the 4.000 MHz band edge; this is true for some forms of
modulation
, but not all, and is challenging to measure accurately. In general, high quality receivers or frequency-selective
RF
power-level meters have better dynamic range, hence more acute signal detection, than all but the best spectrum analyzers, and are excellent for detecting out-of-band emissions when used properly. While some operators reporting out-of-band emissions might have used a wide receiver bandwidth,
receiver
bandwidth expands the measured
transmitter
bandwidth, so the perceived bandwidth seems wider than it actually is: Any measurement of out-of-band emissions using a receiver should be made with it set to a significantly narrower bandwidth than the transmitter's ? for example, a narrow
"CW"
mode.
Inexpensive spectrum analyzers,
spectrum scopes
, and
panadaptors
generally are not useful for measuring bandwidth, either on-air or off-air. Wide detection bandwidth, slow sweep rates, and common, loud, local ambient noise all mask the presumably weak emissions that survive a transmitter's internal filtering. Although voice ("phone") modes like
upper side band
,
amplitude
, or
frequency modulation
transmitted at a nominal 3.999 MHz will certainly modulate across the 4.0 MHz band edge and are against licensing regulations, a few very narrow-band data modes ? like CW ? can be used, as long as the power of the emissions beyond the band edge that get past the transmitting system's filtering remain insignificantly low.
Broadcast interference
[
edit
]
The European 75 m
shortwave broadcast
band overlaps the upper edge of the 80 m ham band allocation in
the Americas
. When it is night on both ends of the transmission path some broadcasters in Asia and Europe can be heard in North America between 3.9?4.0
MHz
. On an
SSB
receiver this produces a tone in the received audio when the station is broadcasting with conventional
amplitude modulation
, or white noise if the station is transmitting
Digital Radio Mondiale
(DRM). Setting an SSB receiver to the exact frequency of the
AM
carrier
can blank out the carrier tone, but the audio signal often can still be heard. If a
DRM
signal is strong enough, its noise may mask weak amateur signals. Most DRM signals occupy 9 or 10
kHz
of bandwidth.
- ^
In each
ITU Region
, a few nations allocate different sub-bands of 3.5?3.8 MHz, 3.5?3.9 MHz, or 3.5?4.0 MHz for amateur use.
- ^
In Australia the upper 3.776?3.800 MHz band segment is a DX window, only allowed for amateurs with advanced licenses.
- ^
In Korea the 3.520?3.525 MHz sub-band is for digital messaging.
[7]
See also
[
edit
]
References
[
edit
]
- ^
"Frequency or wave band allocations"
.
Recommendations for Regulation of Radio
. Third National Radio Conference. 6?10 October 1924. p. 15.
- ^
International Radiotelegraph Convention and General and Supplementary Regulations
(PDF)
. International Radiotelegraph Convention (in French and English). Washington, DC: London, UK: His Majesty's Stationery Office (published 1928). 4 October ? 27 November 1927. Archived from
the original
(PDF)
on 8 March 2014
. Retrieved
25 December
2023
.
- ^
"RAC MF / HF Band Plan"
(PDF)
. Ottawa, ON:
Radio Amateurs of Canada
(RAC). 11 July 2008. Archived from
the original
(PDF)
on 27 November 2010
. Retrieved
1 October
2010
– via RAC Web (rac.ca).
- ^
a
b
IARU Region 1 Bandplan
(Report).
International Amateur Radio Union
Region 1 (IARU-R1)
. Retrieved
January 5,
2010
– via iaru-r1.org.
- ^
a
b
"IARU Region 3 Bandplan"
.
International Amateur Radio Union
Region 3 (IARU-R3). Archived from
the original
on 22 July 2011
. Retrieved
5 January
2010
– via iaru-r3.org.
- ^
JARL Band Plan
(PDF)
(Report). Toshima-ku Tokyo, JP:
Japan Amateur Radio League
(JARL). 25 September 2023 – via jarl.org / jarl.or.jp.
- ^
a
b
KARL Bandplan
(Report). Seoul, KR:
Korean Amateur Radio League
(KARL)
. Retrieved
January 5,
2017
– via karl.or.kr.
- ^
US Amateur Bands
(Report). Newington, CT:
American Radio Relay League
.
Archived
from the original on 7 September 2005
. Retrieved
August 3,
2005
– via ARRLWeb (arrl.org).
- ^
ARRL Band Plans
(Report). Newington, CT:
American Radio Relay League
.
Archived
from the original on 3 August 2005
. Retrieved
3 August
2005
– via ARRLWeb (arrl.org).
|
---|
Range
|
Band
|
ITU Region 1
|
ITU Region 2
|
ITU Region 3
|
LF
|
2200 m
|
135.7?137.8 kHz
|
MF
|
630 m
|
472?479 kHz
|
160 m
|
1.810?1.850 MHz
|
1.800?2.000 MHz
|
HF
|
80 / 75 m
|
3.500?3.800 MHz
|
3.500?4.000 MHz
|
3.500?3.900 MHz
|
60 m
|
5.3515?5.3665 MHz
|
40 m
|
7.000?7.200 MHz
|
7.000?7.300 MHz
|
7.000?7.200 MHz
|
30 m
[
w
]
|
10.100?10.150 MHz
|
20 m
|
14.000?14.350 MHz
|
17 m
[
w
]
|
18.068?18.168 MHz
|
15 m
|
21.000?21.450 MHz
|
12 m
[
w
]
|
24.890?24.990 MHz
|
10 m
|
28.000?29.700 MHz
|
VHF
|
6 m
|
50.000?52.000 MHz
(50.000?54.000 MHz)
[
y
]
|
50.000?54.000 MHz
|
4 m
[
x
]
|
70.000?70.500 MHz
|
?
|
2 m
|
144.000?146.000 MHz
|
144.000?148.000 MHz
|
1.25 m
|
?
|
220.000?225.000 MHz
|
?
|
UHF
|
70 cm
|
430.000?440.000 MHz
|
430.000?440.000 MHz
(420.000?450.000 MHz)
[
y
]
|
33 cm
|
?
|
902.000?928.000 MHz
|
?
|
23 cm
|
1.240?1.300 GHz
|
13 cm
|
2.300?2.450 GHz
|
SHF
|
9 cm
|
3.400?3.475 GHz
[
y
]
|
3.300?3.500 GHz
|
5 cm
|
5.650?5.850 GHz
|
5.650?5.925 GHz
|
5.650?5.850 GHz
|
3 cm
|
10.000?10.500 GHz
|
1.2 cm
|
24.000?24.250 GHz
|
EHF
|
6 mm
|
47.000?47.200 GHz
|
4 mm
[
y
]
|
75.500 GHz
[
x
]
? 81.500 GHz
|
76.000?81.500 GHz
|
2.5 mm
|
122.250?123.000 GHz
|
2 mm
|
134.000?141.000 GHz
|
1 mm
|
241.000?250.000 GHz
|
THF
|
Sub-mm
|
Some administrations have authorized spectrum for amateur use in this region;
others have declined to regulate frequencies above 300 GHz.
|
[
v
] All allocations are subject to variation by country. For simplicity, only common allocations found internationally are listed. See a band's article for specifics.
[
w
] HF allocation created at the 1979
World Administrative Radio Conference
. These are commonly called the "
WARC bands
".
[
x
] This is not mentioned in the
ITU
's
Table of Frequency Allocations
, but many individual administrations have commonly adopted this allocation under
"Article 4.4"
.
[
y
] This includes a currently active
footnote allocation
mentioned in the ITU's
Table of Frequency Allocations
. These allocations may only apply to a group of countries.
|
See also:
Radio spectrum
,
Electromagnetic spectrum
|
|