Frequency Coordination
ITU aligned intermodulation analysis for multi carrier radio systems. 2nd, 3rd, and 5th order products, surface and underground modes, real time system scoring, and an interactive spectrum view.
Intermodulation is the dominant cause of self generated interference in multi carrier radio systems. When two or more transmitters share a site, or when a single radio is exposed to several strong nearby signals, mathematical sums and differences of those carriers appear at predictable frequencies. If one of those products lands on a working channel, the result is in band interference that masks weak signals, breaks up audio, and triggers complaints that are notoriously hard to diagnose once the network is in service.
The noIM₃ Intermodulation Calculator computes 2nd, 3rd, and 5th order intermodulation products for any list of carrier frequencies using ITU aligned methods. It supports both surface and underground analysis modes. Surface mode evaluates the full 2nd, 3rd, and 5th order set typical of open air radio deployments. Underground mode includes both two signal (2F1 minus F2) and three signal (F1 plus F2 minus F3) 3rd order products that dominate in confined environments such as mines, tunnels, and metro radio systems where higher orders are heavily attenuated by structure loss.
Every plan is automatically scored from poor to excellent based on total intermodulation count, critical spacing violations, and per carrier impact. Products are classified as critical (less than 6.25 kHz separation from a working channel), warning (6.25 to 12.5 kHz), or acceptable (12.5 kHz and beyond), giving engineers an immediate system health indicator. An interactive spectrum view plots carriers and products side by side. Configurable presets for VHF Marine, 2m Amateur, UHF CB, PMR446, VHF Low Band, and UHF Repeater plans accelerate common coordination workflows while bulk frequency entry with per carrier bandwidth supports complex multi site analyses.
2nd, 3rd, and 5th order intermodulation products computed using industry standard mathematical models. Underground specific two signal (2F1 minus F2) and three signal (F1 plus F2 minus F3) 3rd order formulas are included to reflect confined environment RF behaviour. Results are categorised by proximity to carrier bandwidth to highlight critical and warning conditions.
Switch between surface radio and underground environments to apply the appropriate analysis model and scoring logic. Underground mode emphasises close frequency carrier interaction and tight bandwidth tolerances common in mining and tunnel communications systems where 3rd order intermodulation dominates.
Every frequency plan is automatically scored from poor to excellent based on total intermodulation count, critical spacing violations, and per carrier impact. Maximum hits per carrier are surfaced. Products are classified as critical, warning, or acceptable so the system health read is immediate rather than buried in a long table.
A built in spectrum viewer plots carrier frequencies alongside calculated 2nd, 3rd, and 5th order products. Zoom, pan, and inspect individual spikes to analyse interference distribution across the band. Frequency span and distribution metrics provide a clear picture of overall spectrum efficiency.
Detailed per carrier analysis shows how many intermodulation products affect each channel, identifying high risk frequencies within the system. Clean carriers are flagged. Heavily impacted channels are prioritised for reassignment during coordination exercises so remediation effort is targeted rather than scattered.
Supports both single carrier and bulk frequency entry with configurable bandwidth per carrier. Built in presets for VHF Marine, 2m Amateur, UHF CB, PMR446, VHF Low Band, and UHF Repeater plans accelerate common coordination workflows while preserving full manual control for complex multi site systems.
Carrier proximity is evaluated against ITU and operator defined separation thresholds. Critical violations (less than 6.25 kHz to a working channel) are surfaced first, followed by warning level proximity (6.25 to 12.5 kHz) and acceptable spacing (12.5 kHz and beyond), so operators can address the most damaging interactions before lower priority issues.
Runs entirely in your browser. No frequency data is transmitted to a server, which matters when the carrier list is operationally sensitive, commercially confidential, or covered by an information security regime that prohibits sending raw spectrum data to third party services.
Reach for the Intermodulation Calculator in any of the following situations.
2nd order (sums and differences of carrier pairs), 3rd order including both two signal (2F1 minus F2) and three signal (F1 plus F2 minus F3) products, and 5th order two signal and three signal products. Underground mode emphasises 3rd order dominance because higher orders are heavily attenuated by structure loss in confined environments.
Surface mode evaluates the full 2nd, 3rd, and 5th order set with scoring weights tuned for open air radio deployments. Underground mode focuses on 3rd order dominance and applies tighter bandwidth tolerances to reflect the confined environment behaviour observed in mining, tunnelling, and metro radio installations. Picking the wrong mode produces either false positives (running surface assumptions in a tunnel) or false negatives (running underground assumptions on a surface site).
The score combines total intermodulation product count, critical spacing violations (products within 6.25 kHz of an active channel), and per carrier impact (maximum hits on a single carrier). The result maps to a poor to excellent band that gives engineers an immediate health read without parsing the full product table.
VHF Marine, 2m Amateur, UHF CB, PMR446, VHF Low Band, and UHF Repeater preset plans are built in. Each preset populates carrier frequencies and bandwidths so common coordination workflows can be analysed in one click. Manual entry remains available for complex or non standard plans.
No. The calculator runs entirely in your browser. No carrier frequencies, bandwidths, or system data are submitted to a server. This matters when the plan is operationally sensitive, commercially confidential, or covered by an information security policy that prohibits sending raw spectrum data to third party services.
The calculator is the right tool for fast multi carrier intermodulation analysis on small to medium plans, with strong educational and demonstration value through the interactive spectrum view and presets. The Frequency Plan Validator is the heavier audit tool for production radio plans, with bandwidth aware proximity zones, a full hit table with formulae and contributors, source and victim impact analysis, and CSV export. Use the calculator for quick analysis and teaching. Use the validator for full audits and report deliverables.
Yes. Bandwidth is configurable per carrier so mixed plans (narrowband VHF alongside wideband UHF, for example) get a fair analysis rather than every channel being treated as the same width.
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