Frequency Sharing by Fixed and Mobile Users in the 4-28 MHz Range.
Final rept. Jul 76-Mar 78,
NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
Pagination or Media Count:
The feasibility of hf fixed and mobile services to share the hf fixed service frequency bands has been assessed. The circuit compatibility of the fixed service with the mobile service on co-channel assignments is dependent on the channel usage U of the interferer and has a minimum value of 1-U. For communication circuits, such as mobile circuits which are operated sporadically, channel usage is low and circuit compatibility is, hence, high. The uniformity in channel usage of a particular mobile system is important in determining opportunities for sharing. When channel usage of the mobile service is high, interference may be reduced to the fixed service by employing space diversity and directive antennas, and by using single sideband modulation SSB for radio telephony. Interference increases in the mobile service when its receiver is within the mainbeam of the interfering fixed transmitter. The difference in maximum fixed service and minimum mobile service transmission power can be minimized by having the mobile service employ narrow band telegraph modulation wherever practical. For specific sunspot activity, month of year, time of day, paths of propagation, the frequencies of concern for interference increase with increasing sunspot number, with increasing path length desired, and for transition from night to day. This is primarily due to increasing path MUF. As the desired path length decreases during the daytime, its lowest usable frequency LUF decreases causing lower and lower frequencies to be subject to interference. Author
- Radio Communications