IntermodIntermod
Input Freqs
Pretty simple. Input up to 40 frequencies (in Mhz) to be included in the intermodulation calculations.
Order
Enter the number of orders that you would like Intermod to calculate. Typically, for our purposes, orders beyond 5 do not produce enough power to interfere with wireless mics.
PB Width (Passband Width)
Assuming that every input frequency has an associated receiver, the field should be filled with the passband width of the associated receiver, in Mhz. From this information the Intermod will automatically calculate the upper and lower passband frequencies. For example, assume an TX frequency of 600MHz with an associated RX at the same frequency. The passband width of the associated receiver is 400Khz (0.400Mhz) Intermod can be set to calculate the upper limit of the passband as 600.200Mhz and the lower passband limit at 599.800Mzh PB Width is only used to calculate passbands.
Passbands and Auto-calculate Passbands
Passbands can be auto-calculated before the intermodulation calculation begins by checking the appropriate check box. Auto-calculate will also clear passbands that do not have a related frequency. If one wants to have Intermod calculate for passbands that do not have a related frequency, Auto-Calculate should be turned off to avoid those passbands being cleared on calculation. The Auto-Calculate checkbox will automatically be checked if Intermod is set to calculate multiple passbands. (See Use Multiple Passbands) The "Calculate PB's" will calculate passbands without running the entire series of intermodulation calculations.
Odd Orders Only
Intermod will only go through the calculation process for Odd orders only (3rds,5ths,7ths,ect.) It does make the calculation process slightly faster. Even orders most often fall outside the passband and are therefore less interesting to the result. If your input frequencies cover a wide range, this should option should not be checked.
Primary Carrier Spacing Requirement
When selected, Intermod will check the input frequencies for the specified spacing. The spacing is checked as the frequencies are entered/changed, and again when the Calculate IM's button is clicked. If the spacing requirement is not met, Intermod will not run the calculations.
A fantastic suggestion from Gary Trenda. With this enabled, Intermod will set up user specified allowable spacing for 3rds and 5ths. For example, if Intermod finds a 3rd or 5th order product inside one of the primary passbands, it is then checked again to see if the product falls within a narrower band as defined by the user. This has the effect of reducing the number of interesting intermodulation products displayed in the All Results tab. Orders higher than 5th are not affected by this selection.
Worst Case Display Filter
Selects what results will be displayed in the Worst Case IM's tab. These filters are applied to the All Results set to derive the Worst Case IM's set.
Direct Hits Only
Worst Case IM's displays only intermodulation products that land directly on an input frequency. This option grays out any further filter selection.
The following filter selections are stackable:
3rd's created by 2 TX
Worst Case IM's displays only intermodulation products that are 3rd order and were created using only 2 input frequencies.
3rd's created by 3 TX
Worst Case IM's displays only intermodulation products that are 3rd order and were created using 3 input frequencies.
5th's created by 2 TX
Worst Case IM's displays only intermodulation products that are 5th order and were created using only 2 input frequencies.
5th's created by 3 TX
Worst Case IM's displays only intermodulation products that are 5th order and were created using only 3 input frequencies.
5th's created by 4 TX
Worst Case IM's displays only intermodulation products that are 5th order and were created using only 4 input frequencies.
Direct Hits
Worst Case IM's displays only intermodulation products that are included in the filter set created by the previous 5 selections AND are direct hits. This is a logical AND. No results will be displayed in the Worst Case IM's display if Direct Hits is the only check box selected.
Calculate IM's
Starts the intermodulation product calculation algorithm. Once the calculation process has started it can't be stopped, so if your calculating a large number of frequencies, be prepared to wait. On my laptop 40 Freqs to 5th order takes about 9 minutes and produces about 13 million calculations. The first time a particular combination of number of frequencies and number of orders is calculated, Intermod first needs to calculate the maximum number of intermodulation products to be expected. It will indicated this by displaying "Calculating Max IM's" next to the progress bar. The progress bar will not function until Max IM's are calculated. This process is slow, but only takes place once per Number of Freqs by Number of Orders combination.
All Results Tab
Displays all results of calculation and displays them per passband. If the total number of results exceeds the maximum allowable size of the Excel spreadsheet, the remaining results will be skipped and not be displayed. Excel can only handle 65536 Rows x 256 Columns.
Worst Cast IM's Tab
Displays the filtered set of results as defined by the Worst Case Display Filter and displays them per passband. A summary of the count of IM's of a particular type is displayed here as well.