The HF Spectrum (2 > 30MHz) has many communication users including commercial/marine and others, most of the users use wideband/broadband antennas which are very inefficient, however, to increase RF power radiation requires the use of resonant antennas on the frequency to be used rather than using a wideband unit.
There is a solution and RFCOMMS have been successful in this field for the past decade in using a newly designed matching transformer that has negligible insertion losses (1.3db) and can be resonant on many spot HF frequencies just by simply changing over the transmission line, this eliminates any tuner or matching losses in the system. Most HF commercial operators will only use 1, 2 or 3 different operating frequencies for day and night operation so only 3 simple wires are needed for the ultimate antenna which is a 1/2 wave dipole, but end fed and being resonant.
The matching unit does not contain any resistors or active components and is constructed using 3 special ferrite cores wound with Mil Def 210 PTFE wire which is then housed in a UV protected enclosure and fully resin potted to protect it from the elements (IP68). The transmission line we use is Kevlar based for strength and durability and is terminated with a UV protected insulator.
An example of the system is as follows: There are many HF SSB Marine frequencies, one being 6224 Khz or 6.224MHz, for this frequency we would use approx 75 feet (22.9Mtrs) which is a half wave length on that frequency, it is also a full wavelength on 12.353MHz which is also another Marine band allocated frequency. So, you have 2 operating frequencies from one transmission line and both have resonant factors. 75 feet can easily be accommodated on most vessels by securing the line from bow to mast top and then to stern, the end matching box can be installed “for” or “aft”. Of course this is just a Marine vessel example but this example can be land based etc. (Note that HF operation is not permitted in the UK, only MOD/ATC and Amateur Radio operators are permitted to use HF but these units can be used by overseas Mil/RS/MOD and other Government organisations).
To add to this if you wish you could have 2 transmission lines one for 6.224 MHz and one for 12.353 MHz and simply change the lines over for day or night operating as the propagation changes, perfect resonance at low cost on 2 frequencies.
The units are VERY cost effective, small, lightweight and totally IP68 rated as they are resin filled. All external parts are Marine A4 Stainless and the kevlar wire has a breaking strain of 90 kgs.
Power handling is 125 watts pep which suits most commercial HF transceivers and can handle ssb/data/ale etc.
(Above) Matching box 2 > 30MHz
(Above) Rugged matching box version with Kevlar line and insulator.
UV resin potted matching unit with Kevlar line etc.
Available as just a matching unit or as a complete antenna built to your frequencies.
Commercial sales only.