where
  I.M. is the newly created intermodulation frequency,
  n_1,2,3.. are integer (+ or -) coefficients
  A, B, C are the existing radio transmit frequencies

If I.M. falls within the bandwidth of a receiver, it may cause interference in that channel.

The intermod order is the sum of the absolute values of the intermodulation coefficients:

  Download the FIntermodSetup.exe file onto a temporary directory in your computer then run FIntermodSetup.exe. You may also run it directly from a CD. Follow on screen instructions as the program loads. FIntermodSetup.exe can be deleted after installation is complete.

  This restricted version of F-Intermod will only calculate the Intermod frequencies for up to 3 channels, and will expire after 7 days. After the trial period expires, you will be prompted to purchase a license key. If you have purchased a license, enter the unlock code when prompted. The registered version will calculate intermods for up to 10000 channels.

INPUT

  First, choose a frequency unit for F-Intermod to use. The default unit is MHz.  To change it to another unit such as kHz or GHz, click Options -> Base Frequency Unit and select the desired unit. This must be done when the input table is empty. 

Channel Name
Enter the channel name or label to a maximum of 12 characters. An entry in this field is not required.

Tx Frequency (Wavelength)
  Enter a transmit frequency (or wavelength if nm unit is selected) for the channel. The maximum and minimum value that can be entered are 999,999.99999 and 0.00001 respectively.

Rx Frequency (Wavelength)
  Enter a receive frequency (or wavelength if nm unit is selected) for the channel. The maximum and minimum value that can be entered is 999,999.99999 and 0.00001 respectively.

Half Bandwidth
  Enter the half bandwidth for the communications channel. For example, if the bandwidth is 30 MHz then enter 15 MHz.  Maximum value is 500,000.00000 and minimum value is 0.00000.  If zero bandwidth is entered, only intermod frequencies that fall exactly on the Tx or Rx values will be displayed.  All output and display bandwidths are half bandwidth values.

Duplex, Half Duplex or Simplex
  Select whether this channel is Full Duplex, Half Duplex or Simplex.  Note that if Simplex is chosen you must enter a transmit OR receive frequency, not both.

Run
  Click to run the calculations for the input data seen in the input table.

Clear
  Clears and resets all the data input and output except for units.

Add
  Click "Add" to enter data (Channel Tx Frequency, Rx Frequency, Half Bandwidth) into the input table.

Delete Row
To delete a channel, click on the row in the input table to select it and then click "Delete".

List Intermod Frequencies
  If "For all channels" is selected, the program calculates all intermod frequencies normally.

  If "For planned channels" is selected, the program will only display the intermod frequencies that the planned channels contribute to. This is useful for calculating the intermod frequencies for new transmitters/receivers being added to an existing site.  A channel can be designated as planned by double clicking on the channel's "Status" entry in the input table.  A planned channel row will be green.

  If "For existing channels" is selected, the program will only use the existing channels in the calculation. Planned channels will not be included and will not be displayed in the output results.

  Channels are labeled "Existing" by default. To change the status to "Planned", double click on that cell in the input table. Planned channels are highlighted in green

Intermod Order
  Enter the intermod order, an integer from 3 to 31 inclusive. Typically intermod orders of less than 7 are used.  For odd intermod order use the pull down selection. For even intermod order, type value into the selection box.

Single Intermod Order
  Select this check box if you want the output to display only intermod order products of order equal to the order selected in the "Intermod Order" box.  If it is not checked, the output will display intermod products up to and including the order entered in the "Intermod Order" box.

Include Tx Frequencies
  Select this check box if you want intermod frequencies to be calculated that fall in the transmitter frequencies bandwidth (transmitter intermod) and receiver frequencies bandwidth.  The program assumes the transmitter bandwidth is the same as the receiver bandwidth.  If the is not selected only intermod frequencies that fall in the receiver bandwidths will be calculated.

Display Channel Name in Results
  Select this check box if you want to see the channel name in the output table rather than its frequency. Channel name size is maximum 12 characters.

List All Intermod
  Select this check box to display all intermod without any receiver or transmitter channel bandwidth filtering.  Output intermod listings can still be filtered into a frequency range by selecting "Specify Output Frequency Range".

Specify Output Frequency Range
  Select this check box to specify a filtered output frequency range and then enter the lower and upper frequency range in the two boxes below it.

Input Table Copy, Paste, Delete Editing
  Right click while the mouse is over the channel input table will produce an additional menu that will allow you to Copy, Paste, Select Column, Select All and Delete.  You can copy one or more entries to and from Excel using this method.

Individual input table cells can be edited directly by double left clicking on the cell.

Table Sorting
  Any input or output table column can be sorted, ascending or descending, by double right clicking on the header of the column to be sorted.
 

Channel Database

  The channel database is an optional feature. In order to access this option, at least one channel entry must be present. To view the extra information for each channel, click on the button beside the channel name box, or click on Options and then click View Channel Info. Here the user may enter extra channel information as labeled. Note: adding this extra information does not affect the intermod calculations in any way.

 There is also the option of exporting the input table to an MS Excel compatible CSV file or to a text file as records. Click on File, then Export Input Table for the options. The text file will display each channel information as separate records.

 When all your channels have been correctly entered, press RUN to execute the program. Depending on factors such as the number of channels, intermod order, bandwidth, and speed of your computer, the run process can take a second or hours.  You may stop the calculations by pressing "CANCEL" at any time.

Output

Sorting
  The output is in column format and is automatically sorted by intermodulation order and frequency.

Columns
  The first column "Order" contains the intermodulation order of calculated intermodulation frequencies.

  The second column "I.Mod.Freq." contains the calculated intermodulation frequencies in units selected.

  The third column "Channel R/T" contains the channel frequency (or name if "Display Channel Name" selected) that is being interfered. The "R" or "T" designates if the intermod is receiver or transmitter intermod.

  The fourth column contains the difference between the calculated Intermod frequency "I.Mod.Freq." and the channel frequency being interfered.  Note, if "List All Intermod" option is selected, then values in this column have no meaning.

  The rest of the columns contain transmit frequency coefficients that produced the listed intermodulation frequency "I.Mod.Freq.".

  Note that the speed of the program depends on the number of Tx and Rx frequencies, intermod level, and bandwidth entered. To speed up the calculations, use a lower intermod level, do not select Include Tx Freq option, or use a faster computer. Also select Single IM Order to reduce output.

Printing and Exporting Output

 To print the output, click File -> Print or press Ctrl P. To view the print preview, click File -> Print Preview. Note that if there are more than 9 transmit frequencies for the input, not all of the output table will be printed due to insufficient paper size. In this case, it is recommended to export the output to a text file, MS Excel compatible CSV file, or another text file which displays the intermod equations rather than the output grid. For example, if the intermod frequency is 138.365 MHz, the file will display the equation for this frequency as

138.36500=(-1)(154.01000)+(1)(149.71000)+(1)(142.66500)

where (-1), (1) and (1), are the intermod coefficients, and 154.01, 149.71 and 142.665 are sample transmit frequencies.

 The CSV file can be opened with any spreadsheet program. It will show both the input and output tables along with the channel database data.

Output Too Large for Grid

  If there is a large amount of data to display, the output table may have insufficient size to display everything. Before the limit is reached, F-Intermod will prompt the user to save the current data before resuming calculations. The data is then saved to 3 files, one for each format (txt, csv and txt displaying intermod equations). This is to save the user time so that instead of running the program 3 times to get all the different outputs, the program can be run once.

 Note: Some spreadsheet programs will be incapable of displaying a very large CSV file.
The text files can be viewed with Microsoft WordPad or any standard text word processor.
For very large text files that WordPad cannot open, use other programs available from the Internet that can open large files such as  Textpad available at www.textpad.com.

Copying

Right click while the mouse is over the output table will produce an additional menu that will allow you to Copy, Paste, Select Column, and Select All.  You can copy one or more entries to the clipboard.  However you cannot  paste to the output table.

File
New (Ctrl+N) - Clears the input and output tables.

Open Tx/Rx Data File (Ctrl+O) - Opens a saved input file. Use this option if you have an input file saved from a previous version of F-Intermod, starting from R3.3.

Open Program File from R3.2, 3.1 or 3.0 - Opens a saved input file from R3.0 to R3.2. You must use this option if you have an input file from these versions. Using the previous Open Program File option will not work.

Save Tx/Rx Data Input (Ctrl+S) - Saves the input table data and options to a text file for future loading with "Open Program File". It is saved with the current filename.

Save Tx/Rx Data Input As... - Saves the input table data and options to a text file for future loading with "Open Program File".  It is saved with the a new filename selected by the user.

Print Preview - Display how the output will be printed.

Print... (Ctrl+P) - Print the current input and output.

Export Channel Information

To MSExcel - Exports the input table data to an MS Excel compatible CSV file.
To Text File - Exports the input table to a text file displaying records rather than a table.

Export Output

To Text File - Exports the output table to a text file.
To MS Excel Compatible CSV File - Exports the output table to a CSV file which can be opened with any spreadsheet program, including MS Excel.
To Text File showing Intermod Equations - Exports the output to a text file showing the Intermod Equations rather than a table.

Exit - Ends the program.

Options
View Channel Info... - Displays the extra channel information dialog box.

Base Frequency Unit - Set the frequency unit to kHz, MHz, GHz, THz or nm. The default unit is mHz. This option can only be set when the input table is empty.

Auto Rx Freq - If checked, then receive frequency will be automatically calculated from the difference between the last transmit and receive frequency pair.  Default difference (on startup) is zero.

Industry
Selecting the appropriate industry will hide non appropriate options for that industry.  Selecting "Radio" industry will show all options.

Help
Guide - Opens this document in your default internet browser.

About - Displays program version and a link to our website, www.telecomengineering.com.

Check for Updates... - Checks for a newer version of F-Intermod at www.telecomengineering.com. If a newer version exists, you will be prompted to download the new installation file. Note: If you have any type of software firewall running on your computer, be sure to allow F-Intermod to access the internet for this option to work.

Radio Intermodulation Examples









Optical Four Wave Mixing Calculations

  This program can be used to calculate fiber optic system inter-channel four wave mixing (FWM) products that can occur when 2 or more wavelengths (channels) are deployed in a DWDM system.  To calculate FWM wavelengths for any DWDM system, setup the software as indicated below.

  Enter all data as described in the "Input" section above with the following below exceptions/modifications:

Menu Industry
  Select Fiber Optic.  This will set the units and options appropriately for FWM calculations.
It also sets the Auto Rx Freq option.  This option provides automatic Rx frequency entry after a Tx frequency is entered.  This reduces the burden of having to enter the same frequency twice.  In order for the frequency to be entered, left click in the Rx box.

Tx Wavelength
  Enter a laser wavelength for a DWDM channel.

Rx Wavelength
  Enter the receiver wavelength for the DWDM channel, it will be the same as the Tx Wavelength for that channel.  With "Option -> Auto Rx Freq" or "Industry -> Fiber Optic" selected, all that is required is to left click in the "Rx Wavelength" box for the value to appear.

Half Bandwidth
  Enter the half bandwidth for the DWDM channel.  Channel spacing can be used as filter bandwidth size and is often the -20 dB bandwidth.  For 1550 nm channel example, if the channel bandwidth is 100 GHz (0.80 nm) then enter 0.40 nm.  For 200 GHz spaced channels is 1.6 nm enter 0.8.  If zero bandwidth is entered, only intermod products that fall exactly on the Rx wavelength will be displayed.  Note, All input, output and display bandwidths are half bandwidth values.

Duplex, Half Duplex or Simplex
  Select Duplex here (even though transmission in one fiber is simplex, for a 2 fiber system). 

Intermod Order
  Enter the intermod order, typically 3 is practical for most systems.

Include Tx Frequencies
  This option is never selected.

List All Intermod
  Select this check box to display all FWM intermods that can be created without any receiver channel bandwidth filtering.  Output intermod listings can still be filtered into a frequency range by selecting "Specify Output Frequency Range".

Specify Output Frequency Range
  Select this check box to specify a filtered output wavelength range and then enter the lower and upper wavelengths in the two boxes.  Typical values entered here would be 1500.0 and 1650.0 nm

FWM Examples








 Computer Platform Requirements and Specifications

General:

Required computer :Windows 98, NT, XP, ME, 2000, Vista
Minimum RAM memory : 128 Mbytes
Hard Drive Space : 10 MB
Resolution : 800x600 VGA Monitor or better
Other peripherals : one printer (not necessary)

Input:

Transmit frequency : 0.00001 to 999,999.99999 for any units kHz, MHz, GHz, THz, nm
Number of transmit freq. : 1 to 10000
Intermodulation order : 2 to 31
Receive frequency : 0.00001 to 999,999.99999 for any units kHz, MHz, GHz, THz, nm
Number of receive freq. : 1 to 10000
Frequency bandwidth : 0.00000 to 999,999.99999 for any units kHz, MHz, GHz, THz, nm

Output:

Intermodulation frequency range : 0.00000 to 999,999.99999 for any units kHz, MHz, GHz, THz, nm
Maximum number of intermodulation output frequency listings : unlimited

Computing time : dependent on intermodulation order, number of transmit frequencies, receiver bandwidth, sorting time and number of listings