80-meter band


80-meter band

The 80 meter or 3.5 MHz band is a core amateur radio frequency band, allocated frequencies from 3.5 to 4.0 MHz in IARU Region 2, and generally 3.5 to 3.8 or 3.9 MHz in Regions 1 and 3 respectively. The portion of the band used for voice communications is sometimes referred to as "75 meters". The 80 meter band was made available to amateurs in the United States by the [http://earlyradiohistory.us/1924conf.htm Third National Radio Conference] on October 10th, 1924. 80 meters is the most popular band for regional communications networks through the late afternoon and night time hours. It 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, depending on atmospheric and ionospheric conditions.

ummary

The 80 meter band is the band of choice for local and regional communication, being the favored home of nets from the same country and for lengthy 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. 80 meter contest operations can make or break a high scoring effort.

In practice, the large physical size of antennas at this frequency – a quarter-wave vertical, for example, is approximately 65 feet/20 meters high – and the difficulty of ensuring significant low angle radiation from antennas to maximize the distance of "hops" are two of the challenges facing amateurs wishing to communicate over longer distances. Most amateurs interested in regional communication use low, wire antennas, such as dipoles, inverted vees or loops on this band, which due to proximity to the ground produce predominantly high-angle radiation, mostly useful for Near Vertical Incidence Skywave and other short distance propagation modes. During the daytime, a station in middle or high latitudes using 100 watts and a simple dipole oe similar antenna can expect a maximum communication range of 200 miles/300 km, perhaps extending to 1,000 miles/1,500 km at night. These ranges are shorter in the tropics, due to increased radio noise from thunderstorms and higher levels of solar radiation increasing signal absorption in the D-layer of the ionosphere.

Global coverage can be routinely achieved during the late Fall and Winter by a station using full legal power and efficient antennas with low angle radiation, such as a 65 foot quarter wave vertical with an extensive radial system. While long distance coverage can be achieved with much less power and antenna efficiency; however, its reliability diminishes proportionately.

Mobile operation is possible, although the relative shortness of a practical mobile antenna (usually less than 10 feet/3 meters) compared to a quarter wavelength results in the need for massive inductive loading to achieve resonance, and exhibits very low radiation resistance, limiting the overall antenna efficiency to less than 10%. Additionally, the large inductance of the loading coil creates a very high Q antenna system, with an extremely narrow bandwidth on the order of 20 kHz or less. In spite of these difficulties (or perhaps "because" of them), dedicated mobile operators enjoy the challenge and routinely contact hundreds of stations, including DX stations at distances of up to 10,000 miles/16,000 km!

Propagation

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 in during darkness hours in midwinter, which can be as much as 300 miles/500 km, rendering communication with some nearby 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 allocation

The International Telecommunications Union allocated the whole 500 kHz from 3.5 to 4 MHz to amateurs in the Americas, and 3.5 to 3.8 or 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 (in MHz):
* Argentina 3.500–3.750, 3.790–3.800
* Australia 3.500–3.700, 3.766–3.800
* Canada 3.500–4.000
* Europe 3.500–3.800
* [http://www.jarl.or.jp/English/6_Band_Plan/JAbandplan.pdf | Japan] 3.500–3.575, 3.599–3.612, 3.680–3.687, 3.702–3.716, 3.745–3.770, 3.791–3.805,
* New Zealand 3.500–3.900
* Russia 3.500–3.800
* United States 3.500–4.000

80 Meter Allocations

Band edge

The highest usable frequency in the 80m band for lower side band phone is 3999 kHz. Depending on the make and model of radio, microphone and audio filtration if any, emissions will typically occupy 3996 - 3999 kHz.

It is a common misconception that using this carrier frequency is not legal as it bleeds across the 4000 kHz band edge. People reporting the bleed over are tuned to 4000 kHz LSB, of which their receiver is still passing 2 kHz of the audio bandwidth. The next logical channel is 4003 kHz lower side band or 4000 kHz upper side band and when the average receiver is tuned to these frequencies no interference or bleed over is encountered. When viewed on a proper piece of test equipment such as a spectrum analyzer it becomes clear that lower side band emissions on 3999 kHz stay inside the band.

Using other phone modes such as upper side band, amplitude or frequency modulation with 3999 kHz as the carrier frequency would modulate across the band edge and are not considered legal. Certain data modes and CW are usable as long as the emission bandwidth does not extend across the band edge.

3995 kHz interference

Deutsche Welle operates on 3995 kHz using Digital Radio Mondiale modulation from Sines, Portugal, Transmitting with an effective radiated power of 90 kW spot beamed at Central Europe. The mode of operation (DRM-17) occupies approximently 9 kHz of bandwidth. When in operation this signal effectively destroys analog phone operations in the upper 10 kHz portion of the 80 meter band.

ee also

Shortwave bands

References

*cite web | title = ARRLWeb: US Amateur Bands | work = | url = http://www.arrl.org/FandES/field/regulations/bands.html | accessmonthday=3 August | accessyear = 2005

*cite web | title = ARRLWeb: ARRL Band Plans | work = | url = http://www.arrl.org/FandES/field/regulations/bandplan.html | accessmonthday=3 August | accessyear = 2005

*cite web | title = RAC Web: Canada HF Band Plan | work = | url = http://www.rac.ca/service/bandplans/RAC_Draft_HF_Band_PlanR1.pdf | accessmonthday = July 22 | accessyear = 2008

*cite web | title = Ham Radio QRP | work = | url = http://www.ac6v.com/qrp.htm#CALL | accessmonthday=3 August | accessyear = 2005

*cite web | title = IARU Region 3 Bandplan | work = | url = http://www.jarl.or.jp/iaru-r3/r3bandplan.doc | accessmonthday=3 August | accessyear = 2005


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