IMP calc

Intermodulation calculator for accurately assessing frequency problems

In locations where several transmitters and receivers are operating, signals will interact by what is referred to as the heterodyne effect; interaction (or intermodulation) products are produced on all sum/difference and product combination frequencies of every signal present. IMP Calc computes the intermodulation products.

Calculating intermodulation has always been a headache for engineers – numerous potential combinations of frequencies have to be cross-checked to identify whether they cause problems at the victims’ receivers. Even with only a handful of  frequencies, the problem can expand beyond the capabilities of the average spreadsheet. This is twofold when signal bandwidths are also considered.

IMP Calc is a simple yet powerful utility which removes the headache of calculating all intermodulation products when checking transmitter interference and receiver susceptibility problems. The tool allows the user to edit frequency listings and add potential interferer-frequencies and receiver-frequencies where intermodulation protection is sought. Each element in the list may be given a name, channel spacing, protection bandwidth and frequency offsets, as well as having planned or commissioned status.

After intermodulation calculation is complete, a full or constrained result listing in the frequency band can be viewed for any combination of 3rd, 5th, 7th and 9th order components. This utility highlights the composition of intermodulation frequencies allowing the engineer to quickly identify problem frequencies. The outputs from IMP Calc can be saved to disk, printed or copied to other applications. The files are stored in comma separated ASCII format, allowing direct manipulation in spreadsheets such as Excel.

  • Calculates 3,5,7 or 9th order intermodulation products
  • Verifies receiver frequencies against potential interferers
  • Imports and exports frequency lists to spreadsheet files
  • Filters products in frequency band of interest
  • Displays frequency spectrum graph
  • Saves transmitter and receivers lists to file
  • Cut and paste lists directly into other applications
  • Prints listings and spectrum graphs

How many frequencies can IMPCalc handle?

There is a limit of 32,000 frequencies, but the user should note that computation times increase significantly as the number of inputs rise. IMPCalc can also only display the first 32,000 results from these calculations, a figure which is affected by the filtering options on the Intermods tab (untick show all intermod, add frequency limits etc.).

While there is a temptation to add as many frequencies  as possible for a site, users are recommended to restrict the number of frequencies to the minimum required for a valid site configuration as this will help to generate more useful results. For example, if a transceiver can operate on two adjacent channels then these could be added to the list and intermodulation products between these channels would be computed. However, it is unlikely that both channels will operate simultaneously, which would result in more products being computed than necessary.

I have changed my computer; will the original activation code for IMPCalc work on my new computer?

The activation code is specific to the original machine IMPCalc was installed on. However, the software licence is transferable but users are advised to follow the process outlined in the ’Getting Started Guide’. If the transfer is unsuccessful a new activation code will be supplied. Please contact ATDI providing reason for the request.

IMPCalc is requesting an activation code having previously worked?

Providing your copy of IMPCalc is not an evaluation copy the most likely cause are changes to user profiles or upgrades to hardware. These will cause the activation code to fail and a new code should be requested from ATDI.