VLF (very low frequency) band
VLF (very low frequency) band creates an almost equal conditions for each radio amateur, no matter how much money he can spend on the equipment or how much free space is available. Indeed, when the wavelength of more than 2 km, to implement a full-sized antenna is difficult, but possible. Unable to another - to provide an acceptable installation height. And no one can complain about poor relief - bass well into even through solid rock.
Experiments with the VLF-band can bring quite tangible practical benefits to the organization of underground radio rescue services.
Always bear in mind that radio amateurs in every country are experiencing increasing pressure on frequency allocation and justification of the use of potentially valuable frequencies - useful experience and an efficient implementation of the results for public purposes.
Equal conditions VLF-band creates for used equipment. Happy owners of modern industrial transnverov at best be able to use them for admission (usually the receiver of the device works with 30 kHz). For this band, the converter can be manufactured, for example 136 kHz to 14 MHz, or receiver (transceiver) direct conversion.
Additional advantages will use noise blanker'a, although atmospheric disturbances are often irregular, and more effective would be an ordinary limiter. The greatest effect can be achieved by using a program such as DSP, or other powerful software for audio processing. Perhaps an ideal solution would be to use this band of coherent Telegraph that in the era of indiscriminate use of PC to radio stations is very logical. As for the transmitter (transceiver), many who want to work in the VLF have to make it yourself.
The problem is not the most difficult, given the low (almost audible) frequency band and 2.5 kHz. However, a narrow strip imposes high demands on the spectrum of the emitted signal. It's hard to believe how active will be used this band, but a low-quality transmitter will make it impossible for a great many radio amateurs example CW-signal at 60 characters per minute and a rise time of 5 ms takes on the air of about 150 Hz, while the same CW is the signal rise time 2 vie would take 375 Hz.
And what about the VLF-band in other countries?
In some other European countries fans allocated the same frequency portion. Hams UK further experimented in the band 71.6 ... 74 4 kHz. However, the work is available only to holders of Class A license Power - 1 W ERP (m e. The effective power, taking into account the efficiency of the antenna. Therefore, the transmitter output power can be several hundred watts.) Judging by the publications, using even a small loop antenna succeed QSO at a distance of 100 km.
With regard to the VLF-band in the US, there is such a band, as it is distributed for any experimental CW-ties, and for its use of a license is not required. Bandwidth - 160 ... 190 kHz, the so-called 1750-meter band. There are serious limitations on the transmitter power (1 watt input), and the total length of the transmission line and the antenna can not exceed 15 meters area between 180 and 190 kHz, it is also used for CW-beacons.
You can almost be sure that the new band will find its supporters, despite the limited band of possible QSO - because fans are experimenting at centimeter wavelengths, admiring each overlapped kilometer distance between correspondents.