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Co Channel Separation

Page history last edited by PBworks 12 years, 9 months ago

Co Channel Separation Data:


Since there is very little data to be found on the exact performance of 10 watt stations on the Medium Wave Band and their contour areas. The following data was utilized as a comparison method for determining the average radius for the LPAM Service:


§ 90.242 Traveler's Information Stations. (b) Technical standards. Section 5 : iii ~ (Regarding co channel station separation for TIS stations.) "15.0 km (9.3 miles) for the case when both stations are using conventional (vertical) antennas."


Based upon the separation of the 10 watt TIS stations, the radius of coverage to the fringe area is:


9.3 Miles /2 = 4.65 miles (7.4865 km)


An examination of the transmitters from various manufactures shows that the TIS transmitter does not utilize a ground radial system other than a grounding rod if used. These stations are sometimes located right next to a highway and are outdoor located transmitters in many case. Wherein ground radials are not feasible for use. The antenna height is similar to that for suggested LPAM use. The LPAM antenna is rounded off to an even 50 feet and slightly higher than the TIS station by about 1 foot.


Given the requested use of capacitance hats and ground radials systems by the LPAM community advocates. The fringe area radius for each LPAM channel when compared to the similar power level and antenna height of the TIS station in § 90.242, the LPAM station radius is moved out to 6 miles. This is due to slightly more efficient LPAM station set ups with antenna capacitance hats and ground radial systems. This does not mean that the LPAM station will be effectively heard at this radius. And the LPAM service must agree to suffer interference at it's fringe area. And not to cause interference to other stations in it's region.


This then means that the best overall minimum separation between co channel LPAM stations is 12 miles (19.32 km). Stations operating adjacent channel to each other shall not be closer than 6 miles to each other.


In the TIS specifications of § 90.242 the electrical field intensity limitation is 2.5 mV/m at one-mile. With the improvements made to the LAPM station as compared to the TIS station the estimated LAPM electrical field intensity limitation is 3mV/m at one mile. The use of directional type antennas for resolving regional problems where the antennas in this service are all too short for efficiency, will mean that the figure for such possbile use directional antennas will be in the arena of 3.25mV to 3.5mV/m at one mile.


Such antennas as are recommended for use in this service have a gain figure less than that of a full sized 1/4 wavelength radiator which is 3 dB over a isotropic radiator. Hence the gain of all antennas for use in this service will have a gain less than 3 dB.



3mV/m at one mile, average field strength intensity shall then be used as the approximate limitation for the specified vertical radiator for this service. 3.5mV/m at one mile shall be the limitation for average field strength intensity where directional antennas are used in the LPAM Service.



Suggestion: After the service is launched, the study of the average field intensity of actual stations and the various antennas for possible use will lead to data for compiling and comparing to make a finalized rule on the actual field intensity. Stations who are proficient at such studies should be able to comment on such data as the have compiled on their stations for FCC use. The data on the vertical antenna can only apply to stations who use the full antenna height figure of 50 foot. Shorter heights will not be of use in defining limitations.



For the above reasons, and with regards to the Traveler's Information Stations Service no LPAM Station shall operate co channel with a TIS station no closer than 15 miles form a TIS station.


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