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Creating a channel plan to avoid third-order intermodulation interference

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Using this program allows you to create a channel plan in order to avoid third-order intermodulation interference and the near-far problem, which can be an issue when many channels are being used in the same area. Third-order intermodulation interference is particularly difficult to avoid since it occurs in the vicinity of the working frequency, causing communication errors. In order to prevent this, it is necessary to select the most appropriate frequency.

Creating a channel plan to avoid third-order intermodulation interference

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Instructions

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To create a channel plan, set the various data for the first frequency band to use. Next select the channels. There are two ways to set the frequency band data; enter the data in each input field, or select the frequency band from the selection box if you already know it.

Setting the frequency band data

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1. Using the selection box
If you use the "Band selection" box, you can set the representative frequency band for each country. When you set the frequency band, the starting channel and channel span are set automatically.

2. Entering data in the data input field
Enter the channel number of the frequency band for the country in which you are making a channel plan, and enter the corresponding frequency and channel span. After entering each item, press the "Enter"; key on your keyboard, or click the "Initialize" button.

* "Starting channels" : Enter the starting channel number of the frequency band.
* "End channels": Enter the end channel number of the frequency band.
* "Starting frequency": Be sure to enter the frequency of the starting channel.
* "Channel span" : Enter the channel separation determined by the frequency band used.
* "Forbidden frequency bands" : The default is 1-fold. Select a suitable value for the selectivity of the receiver.
* "Initialize" button: Initializes the display with the set value.

Selecting a channel

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Click the checkbox of a frequency to select it.

* Green: Selected frequencies are highlighted in green. Checked channels shown in green are channels that can be used at the same time in the same area.
* Yellow: Indicates channels that may be affected by third-order intermodulation interference or by the near-far problem. Do not use these channels.
* Red: Red indicates that third-order intermodulation interference will occur between channels. If a channel is shown in red, click the checkbox again to deselect it, and choose another channel.

Miscellaneous

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The Japanese 800 MHz frequency band
With Japan's 800 MHz frequency band, you can use the "Plan support" box. This creates a channel plan automatically for the frequency band that you set. In this case, the "Forbidden frequency bands" is just one adjacent channel. If you select plan with "Plan support", distinguish between a plan where the total number of channels in the frequency band width is 30 or less, and 30 or more. If the plan is not created completely, check the unchecked items to complete it.

About the near-far problem
In order to avoid the near-far problem, it is necessary to adjust the frequency bands in the "Forbidden frequency bands". If the channels of specific low power radio equipment with a narrow channel span (e.g., 12.5 kHz) are not separated by several channels, mutual adverse effects may arise with other radio equipment located a short distance away.

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