The properties of each amateur radio band vary for a variety of reasons. Everything from the propagation characteristics to the band planning, and the different spectrum allocations for different countries vary.
These and other factors mean that the contacts made on these different bands will be quite different. On some amateur bands long distance contacts will be plentiful, whereas on other ham radio bands only local contact may be possible. Again on some ham radio bands, modes of operation that can be deciphered at very low signal levels may be used, but on other amateur radio bands signals may be very strong.
There are very many factors that affect the way in which the different amateur radio bands may be used, but spectrum allocation characteristics and differences around the globe, band planning, and the propagation characteristics are some of the main factors.
Radio spectrum and ham radio bands
The radio spectrum extends over a vast portion of the overall electromagnetic spectrum. There are very many amateur radio bands in most parts of the spectrum. Naturally amateur radio band allocations need to fit in with other users and with the UHF portion of the spectrum being widely used for many other forms of communication including cellular telecommunications and other forms of short range communications, there is significant pressure on allocations in these and some other parts of the radio spectrum.
IN recent years, with the move of many radio communications services to higher frequencies, there have been more ham radio band allocations in the LF, MF, and HF portions of the radio spectrum. This has given a considerable amount of additional space to radio amateurs and increased the variety of bands available.
Bands in the UHF section of the spectrum are coming under increasing pressure for reallocation to other users. Nevertheless, there is still a large amount of spectrum available.
Propagation & ham radio bands
One of the key elements that determines the characteristics of the different ham radio bands is the propagation conditions that prevalent for the band. The propagation conditions will govern whether signals cane be heard over vast distances and around the globe, or whether they can be heard over distances that are a little more than the line of sight.
There are several types of radio signal propagation that can be experienced. Some of the main types include:
- Ground wave: This type of propagation is generally experienced on any amateur radio bands in the LF portion of the spectrum. It is used by LF and MF broadcast stations.
Note on Ground Wave propagation:
Ground wave propagation occurs when signals follow the contour of the Earth, bending so that the signals are able to be detected beyond the horizon. It is this form of propagation that is used by LF and MF, Long Wave and Medium Wave Band broadcast stations..
Read more about Ground Wave propagation
- Ionospheric propagation: Ionospheric propagation generally affects signals in what are often termed the short wave bands, although this type of propagation also affects amateur radio bands at the bottom of the VHF portion of the spectrum as well.
Note on Ionospheric propagation:
The ionosphere exists in the upper reaches of the atmosphere extending to altitudes of 400 km or more. The different regions of the ionosphere can affect radio signals refracting them so that they return to Earth. In this way, signals can be heard at distances ranging from a few hundred kilometres to the other side of the globe.
Read more about Ionospheric propagation
- Tropospheric propagation: Tropospheric propagation affects the ham radio bands upwards from 30 MHz. At times, there are "lifts" in conditions which enable signals to be heard over very much greater distances than are normal.
Note on Tropospheric propagation:
The troposphere is the region of the atmosphere closest to the earth. It is found that the refractive index of the air reduces slightly with increasing altitude. This effect can also be enhanced and modified by weather conditions. As electromagnetic waves bend towards the areas of high refractive index, it is found that radio signals are affected by these changes and can travel over distances beyond the horizon.
Read more about Tropospheric propagation
There are amateur radio bands that can be found in virtually all areas of the radio spectrum:
- 136 kHz band: There are a few bands in the LF portion of the radio spectrum. The 136 kHz band is one off the most established. Read more about 136 kHz amateur band.
- HF amateur radio bands: The HF amateur radio bands carry most of the long distance traffic. Dependent upon the band, contacts can easily be made all over the globe as a result of the ionospheric propagation that is used. The propagation conditions will vary according to a variety of factors, but it is normally possible to make contacts over distances of a thousand miles or more at most times, and often contacts can be made over much greater distances, even to the other side of the globe. Read more about HF amateur radio bands.
- VHF amateur radio bands: Ionospheric propagation does not generally affect these amateur radio bands to the same extent. Although contacts in bands at the lower end of the VHF portion of the spectrum are affected by ionospheric propagation, especially during periods of the solar maximum, in general tropospheric propagation is more prevalent. As a result, distances achievable on these ham radio bands are much reduced on those experienced on the HF bands. Read more about VHF ham radio bands.
- UHF ham radio bands: The UHF amateur radio bands provide a unique opportunity for many contacts to be made. In general contacts tend to be over distances of 30 miles or more, but on occasions signals may travel over much greater distances. Read more about UHF ham radio bands.
In view of all the differences in allocations, propagation usage and the like, each band has its own characteristics and can be used differently. Having a knowledge of the bands enables the best use to be made of each opportunity and thereby making the most of the hobby.