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.
Included in the 14-day Pro trial on every new account. No credit card.
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 evaluates 2nd order and both 3rd order families, two signal (2F1 minus F2) and three signal (F1 plus F2 minus F3), and omits 5th order, because the 5th order three signal family is effectively un-plannable and the two signal product sits below the noise floor once leaky feeder coupling loss and cascade amplifier IM rejection are counted. That is the product set for leaky feeder systems in mines, tunnels, and metro networks.
Every plan is automatically scored from poor to excellent based on critical spacing violations, the outside tier counts and per carrier impact. Each product is graded against the victim carrier’s own channel width: inside half that width is critical, then three widening zones at 12.5, 25 and 50 kHz beyond it. Because the threshold follows the carrier rather than a fixed number, the same tiering works for 6.25 kHz narrowband and for a wide channel, and a single minimum separation can replace it when a signal occupies less than its channel. Any carrier can be switched out of the analysis without being deleted, an interactive spectrum view plots carriers and products side by side, and carriers can be typed, uploaded as CSV, or imported from the ACMA register.
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 evaluates 2nd and 3rd order products and omits 5th order, takes harmonics from every carrier rather than the transmit set, and drops the TX/RX role filter, because leaky feeder coupling brings transmit and receive into the same level range. A cross band products switch limits mixing to carriers of the same direction when a diplexed line amplifier keeps transmit and receive in separate gain stages.
Every frequency plan is automatically scored from poor to excellent. Critical products, those inside a receiver’s passband, are uncapped because each one is a real finding. The warning, marginal and acceptable tiers grow with the cube of the carrier count, so they are capped at 15, 5 and 5 points: a plan with no product in any passband scores 75 or better whatever its size, instead of a large site with hundreds of adjacent channel products and nothing in band reading as zero. Maximum hits per carrier are surfaced, so the 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, jump to the TX or RX band, 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.
A switch on every row of the carrier table takes that carrier out of the analysis without deleting it. Use it to ask what the site looks like without a service: a licence that is not being renewed, a repeater coming out, or a candidate frequency you want to try against the incumbents. The carrier keeps its bandwidth, role, disposition and register details and is saved with the plan, and while it is off it makes no products and is assessed against none, so the score, every count, the spectrum and the proposal comparison describe the switched on carriers only. The title bar says how many are off, one click puts them all back, and the CSV and PDF name them so an exclusion never reads as an omission.
Add carriers one at a time with a label, value, unit, per carrier bandwidth and direction, or upload a whole plan from a CSV template. An exported plan can be edited and re-imported, so a frequency list maintained elsewhere stays the source of truth. Share copies a link that carries the whole plan, up to 40 carriers, so a colleague opens exactly what you see with nothing to upload.
Search the ACMA register by site ID, site name, licence number or postcode and import the licensed services already on a shared tower as carriers, instead of transcribing a licence schedule by hand. Import everything on the site, or restrict it by band, frequency range, device type or licensee, with band edges taken from the RALI LM 08 coordination bands. The register device type sets the carrier role, so transmit records become intermod contributors and receive records become victims.
Mark which carriers are already on the tower and which are the change you are proposing, and every intermodulation product is attributed to a party. Products your proposal puts into a receiver already on site are separated from products the existing site puts into a receiver you are adding, because those are the same arithmetic and completely different conversations: one is a negotiation with a licensee who can refuse you, the other is a channel choice nobody else is involved in. Interference within your own plan is listed separately again, since both ends are yours to move. The site is scored before and after your change, the affected licensee is named on every product, and the whole attribution carries into the CSV export and the PDF report.
Nothing is imported until you have seen it. The preview reports how many register records were selected and itemises every exclusion by cause, estimates the intermod product count before the analysis runs, and flags a carrier set whose span is too wide for the services to share hardware. Each imported carrier keeps its licence number, licensee, site and licensed EIRP, and that trail appears in the CSV export and the PDF report so a licensed service and a proposed one are never mistaken for each other.
Each product is graded against the victim carrier’s own channel width rather than a fixed number: inside half that width is critical, then warning, marginal and acceptable zones at 12.5, 25 and 50 kHz beyond it. A single minimum separation can replace the half width for every carrier, which suits a signal that occupies less than its channel (a TETRA carrier occupies about 18 kHz of a 25 kHz channel) and lets you check a plan at the separation the Frequency Coordination Tool planned it to. A product exactly on the boundary is at the passband edge rather than inside it, so it passes unless you switch Knife edge OK off to refuse plans with zero margin. Critical hits are surfaced first, so the most damaging interactions are addressed before lower priority ones.
Every product, tier and score is computed in your browser; nothing about your carriers is sent anywhere to run the analysis. Three things do talk to a server, and each sends only what it must: the optional ACMA site import sends your search and returns the public register records for that site, saving a project to your account stores the plan against your login so it follows you between devices, and Share puts the plan into the link you copy. Work on a plan without saving it to a project and it stays on this device.
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 evaluates 2nd and 3rd order and omits 5th order: the 5th order three signal family is effectively un-plannable, and the two signal product sits below the noise floor once leaky feeder coupling loss and cascade amplifier IM rejection are counted.
Surface mode evaluates the full 2nd, 3rd, and 5th order set with scoring weights tuned for open air radio deployments. Underground mode evaluates 2nd and 3rd order, omits 5th order, takes harmonics from every carrier, and drops the TX/RX role filter so every carrier is both a source and a victim, the way a leaky feeder behaves, since the cable brings transmit and receive into the same level range. Picking the wrong mode produces either false positives (running surface assumptions in a tunnel) or false negatives (running underground assumptions on a surface site).
Critical products, those landing inside a victim carrier’s passband, cost points without limit, because each one is a real finding and more of them really is worse. The warning, marginal and acceptable tiers describe products outside the passband and their count grows with the cube of the carrier count, so they are capped at 15, 5 and 5 points. A plan with no critical product therefore scores 75 or better whatever its size. The result maps to a poor to excellent band that gives an immediate health read without parsing the full product table.
Yes. Every row of the carrier table has a switch. A switched off carrier keeps its bandwidth, role, disposition and register details, is saved with the plan, and comes back with one click. While it is off it makes no products and no product is assessed against it, so every number on screen describes the switched on carriers only. The title bar says how many are off, and the CSV and PDF name them so a reader can tell an exclusion from an omission.
It replaces half the channel width as the boundary of the critical tier, for every carrier at once. Leave it blank and each carrier is graded against half its own bandwidth, which is what the tool has always done. Set it when the occupied bandwidth is narrower than the channel, or to the IM separation you planned against in the Frequency Coordination Tool so the two tools grade a plan the same way. Knife edge OK, on by default, decides whether a product sitting exactly on that boundary passes; switch it off to refuse a plan that clears its limit by nothing at all.
Type them one at a time, upload a plan from a CSV template, open a link a colleague shared, or import a site from the ACMA register by site ID, name, licence number or postcode. A register import brings the licensed services on a shared tower in as carriers, with each one keeping its licence number, licensee, site and licensed EIRP, so a coordination study starts from what is actually on the structure rather than from a hand transcribed licence schedule.
Not to run the analysis: every product, tier and score is computed in your browser. Three things do send data, each only what it needs. The optional ACMA site import sends your search and returns the public register records for that site. Saving a project to your account stores the plan against your login so it follows you between devices. Share puts the plan into the link you copy, with register provenance stripped. Work on a plan without saving it to a project and it stays on this device.
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 it is the only one of the two that imports a site from the ACMA register, attributes findings to a party, and switches a carrier in and out. 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.
Included in the 14-day Pro trial on every new account. No credit card.
