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Amateur Radio Gets Secondary MF Allocation at WRC-12

dtmos (447842) writes | more than 2 years ago

News 1

dtmos (447842) writes "The ARRL is reporting that "delegates attending the 2012 World Radiocommunication Conference (WRC-12) in Geneva have approved a new 7-kilohertz-wide secondary allocation between 472-479 kHz for the Amateur Radio Service." This band, below the AM broadcast band, will retain its primary ship-to-shore and radionavigation beacon allocation. Due to the unique propagation characteristics of this part of the spectrum, an allocation has long been desired by the amateur radio community. Much as moonbounce and meteor scatter have produced their own amateur digital communication protocols (OSS under the Gnu GPL, of course), I expect the unique channel impairments of this band will lead to the development of dedicated digital communication schemes (beyond QRSS)."

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Excellent News (1)

Muad'Dave (255648) | more than 2 years ago | (#39044025)

The footnotes are interesting - lots of countries will not be allowing this allocation due to its primary use by the maritime mobile and aeronautical radionavigation services, and some countries have conflicting allocations for all but the upper 2KHz of the new allocation. Band planners should make the upper 2 KHz the DX window.

Also note the the maximum EIRP (effective isotropic radiated power) limit is 1 Watt, with the option of allow 5 Watts for stations 800+km from countries that have conflicting allocations. That may sound like very little power, but at those freqs it would take a mammoth antenna to get that sort of EIRP. this PDF [bldrdoc.gov] discusses MF antennas, and in particular measures the gain of a beast of an antenna used for DGPS, a 1m whip, and a quarter-wave monopole (haha - a monopole a 820 feet high). Start on page 34. The short answer: to get 5W EIRP into a -21.3dBi 1m whip (matching issues aside), you'd need 675 Watts at the transmitter. That's only 0.7% efficiency. Ugh.

The DGPS antenna was described as follows:

The monopole antenna is
a tapered triangular shaped steel tower consisting of steel tubing 1.52 cm in diameter. The monopole
length is 91.16 meters which is only 0.0912 wavelength at 300 kHz. The cross section of the
monopole is an equilateral triangle measuring 0.61 meters on a side for most of its length and is
tapered to a point on each end. There is a copper radial wire ground screen with 120 radials of 0.32
cm diameter that are each 100 meters in length. There are also twelve copper top-loading elements
approximately 138 meters in length symmetrically located around the monopole extending from the
top of the monopole down to the ground just outside but not touching the edge of the radial wire
ground screen. The top-loading elements are 0.95 cm in diameter.

If you can erect a 300+ foot antenna, then you can get away with using 5W input to get 5W EIRP. Most of us will have to do with less efficient antennas!

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