About VHF radio communicationsVHF band was an early choice for manpack radios used by ground troops to communicate within a local eight kilometer (five mile) area or so.
The VHF frequency band is defined as the frequency range from 30 to 300MHz. This means that the size of antennas and tuning components used in VHF radio are much smaller and lighter than those of HF radios. This is a big advantage for manpack radios. The higher frequency and shorter wavelengths of VHF radios have a profound effect on radio range.
Unlike HF, VHF transmissions lack the ability to ultilise the Ionosphere and are limited to line-of-sight (LOS) communication. This reduces radio emission clutter throughout an extended battlefield and limits the vulnerability to unfriendly interception.
The wider channel bandwidth capabilities of VHF radios increase the efficiency of coding and encryption schemes and allow greater data throughput than that of HF radios.
Wider bandwidth and limited range make these radios ideal for squad-to-squad communications. Radio Wave Propagation Ground waves consist of three components:
surface waves, ground-reflected waves and direct waves.
travel along the surface of the earth, reaching beyond the horizon. Eventually, the earth absorbs surface wave energy.
The frequency and conductivity of the surface over which the waves travel largely determine the effective range of surface waves. Absorption increases with frequency.
are the portion of the propagated wave that is reflected from the surface of the earth between the transmitter and receiver.
Direct waves travel in a straight line, becoming weaker as distance increases. They may be bent, or refracted, by the atmosphere, which extends their useful range slightly beyond the horizon.
Transmitting and receiving antennas must be able to “see” each other for communications to take place, so antenna height is critical in determining range. Because of this, direct waves are sometimes known as line-of-sight (LOS) waves.
VHF waves can be reflected off of dense surfaces like rocks or conductive earth, just like a beam of light can be reflected off a wall or a ceiling. Sometimes several paths exist between a transmitting and receiving antenna.
VHF Wave Ducting
The suggested limits on LOS range are sometimes exceeded in practice. One of the principal reasons for this is an effect called “ducting.”
Under fair, dry, and moderate weather conditions; the slight variations in air density have negligible effects on the path of radio waves passing through it.
Frequently there are abrupt changes in air density due to weather fronts passing over an area or the heavy moisture burden of rain clouds. In such cases VHF radio waves can bend or duct between air layers of different densities. Sometimes this ducting bends the radio waves downward so that the radio waves tend to follow the curvature of the earth. In such cases the LOS range is considerably greater than the optical LOS range.
This type of wave propagation is impossible to predict; it is not practical to plan on it for range improvement. However, when ducting conditions exit, they generally do so for hours at a time
Tactical operations rely on HF radio to provide secure and highly reliable communications over long distances in demanding applications and environments.
Barrett HF radio is secure, autonomous and resistant to jamming than other communications mediums. Configurable as a manpack, mobile vehicle or fixed base station all Barrett HF systems use the same keypads and front panel, specifically designed for users who do not have, or need, a lot of training.
Low band VHF radio communications is specially designed for multi-role tactical military and security applications, communications where communication between operators is up to 5km.
Barrett VHF is configurable as a 5 W Hand portable radio, 25 W Manpack radio, 50 W Mobile, 50 W Base station and 50 W Re-broadcast system for range extension or for use in mountainous regions where typically VHF communications is restricted due to the terrain.
Barrett offers a range of interoperability solutions between radio and telephone networks, HF and VHF radio systems and options that are radio and crypto agnostic.
These solutions can enable users to re-commission legacy products with latest technologies or enable collaborative forces to communicate with little need for additional infrastructure.
Our turnkey network design team work with the client’s system requirements and produce an initial technical proposal which, once client approved, develops into the detailed technical document with system manuals and full installation programs.
Each turnkey solution is designed specifically for the client, with some solutions incorporating remote sited HF transmitters and receivers linked to landlines or microwave communications, operator consoles, custom built interfaces and MIL-STD HF data systems including 5066 stack based systems.