Microwave Radio Transmission Design Guide
A practical guide for engineers planning or building a microwave-based transmission system, with a special eye toward international standards.
TABLE OF CONTENTS Microwave Radio Transmission Design Guide
Section 7.6: Frequency Channel Planning
7.6 Frequency Channel Planning
Recommendations specifying the individual radio channel are made by the Radiocommunications sector of the ITU. These JTU-R Recommendations specify the center frequency of the band, the T/R spacing, the adjacent channel spacing (copolar and cross-polar), and the number of channels.
7.6.1 Basic ITU Arrangements
The basic frequency arrangement set by the ITU-R is shown in Figure 7.6.
Figure 7.6: ITU-R frequency plan arrangement diagram.
The center frequency ( f 0) is the midband frequency around which the channels are arranged. A number of channels with a specific channel spacing are identified across the frequency hand of that specific plan.
Sometimes the channels are spaced with alternate polarizations. One therefore needs to be careful when specifying channel spacing requirements whether it is the copolar or cross-polar spacing that is being referenced. A safety gap (center gap) is also specified between the top frequency of the transmit-low frequencies and the bottom frequency of the transmit-high frequencies.
The ITU-R plans are usually provided with the basic configuration showing the center frequency f 0 the channel spacing, the T/R spacing, and the overall frequency band. A formula is then provided from which one can calculate the actual frequencies themselves. The actual frequencies for an international connection [1] in the frequency band 7425 MHz to 7725 MHz using f 0 of 7575 MHz is calculated as follows:
| (7.a) |  |
Hence,
| (7.b) |  |
It can be seen that the channel spacing is (7435 - 7428) 7 MHz and the T/R spacing...
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