The electro-magnetic frequency spectrum is shared by civil, government, and military users of all nations according to International Telecommunications Union (ITU) radio regulations. For all practical purposes, the frequency spectrum currently usable for communications now extends from about 3Hz to about 300GHz. This does not take into account experiments with laser communications occurring at around 100 TerraHertz. The 3Hz to 300GHz range has been split into "bands". The frequency band standard is described in the International Telecommunications Union radio regulations; the table below shows the bands and their designations (VHF+ is "highlighted"):

For amateur radio purposes, there are a series of frequency allocations for the Amateur Radio Service and sharing arrangements with other radio services. Details can be found on the ARRL website. These fall in the frequency bands shown in the table above, beginning in the MF portion of the spectrum at 1800KHz (1.8MHZ) and continuing past the EHF band beyond 300GHz.

Each amateur band exhibits slightly different characteristics, primarily seen as differences in the way the radio signal at that frequency gets from the transmitter to the receiver. This is called "radio propagation", and it is how radio energy travels from one point to another. This propagation of radio transmissions has presented a fascination and an area of study which began with Hertz and Marconi hundreds of years ago and continues to this day. The bands above 30MHz, not usually subject to shortwave, or long-distance ionospheric propagation, present a particular challenge, and that is why this web site, and the group of folks it represents, are primarily concerned with "VHF+", or the amateur radio bands starting with 50MHz and going up in frequency.

"VHF+" is that portion of the radio frquency specturm illustrated by the highlighted portion of the table above. There are 18 VHF+ amateur bands and their frequencies and designations are shown in a detailed chart. What makes VHF+ so interesting is that each band has its own set of propagation characteristics and modes. These are described in the propagation tutorial elsewhere on this site. For the purposes of this page, we can say that the "normal" direct propagation modes, such as groundwave or line-of-sight ("LOS" - when the transmitting antenna can "see" the receiving antenna), are present almost any time on all bands. On some occasions which, while not uncommon do not happen all that often, however, there are special propagation modes which extend radio communication beyond those distances normally expected; as noted above, this is when VHF+ really becomes fun! Sporadic ionospheric propagation, for example, occurs on frequencies from 50MHz through 225MHz. F-layer (long-distance, shortwave) propagation has been observed as high as 144MHz, while E-layer (a layer of the ionosphere lower in altitude than the F-layer which results in distances about half that of F-layer) propagation has been observed as high as 222MHz.

It is the challenge of communicating at frequencies for which propagation is normally limited that grabs the interest of the VHF+ ham community. The "normal" maximum distance for propagation between two WELL equipped (several hundred watts and "big" antennas) 144MHz SSB stations is about 500 miles. On occasion, the 2M band "opens" and contacts over 1200 or more miles become possible. Ham radio operators on the 10GHz band in San Antonio Texas point their high-gain antennas (30+dB) at a rain storm to the northeast and talk 300+ miles with hams north of Dallas who are pointing their high-gain antennas at the same rain storm located southeast of them. A duct opens across the Gulf of Mexico, allowing hams is Texas to talk on 1296MHz and higher frequencies with hams in Florida, a feat not possible under normal conditions. It is the anamalous propagation which draws us to these frequencies. "Who ya gonna talk to on those bands?" is the oft-heard question. Normally, not a whole lot of folks, but when that band "opens" it's like being a kid in a choclate factory! Watch out, America!