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Frequency Coordination

Frequency Plan Optimiser

Minimise intermodulation in existing radio plans through precision channel shifts. No hardware changes, no full redesign, just a cleaner plan within your installed constraints.

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System type in the top bar, with the panel open on the Carriers tab.
System type in the top bar, with the panel open on the Carriers tab.
Single entry for a pair or a single carrier with a role; Bulk for the CSV template or pasted rows.
Single entry for a pair or a single carrier with a role; Bulk for the CSV template or pasted rows.
Setup tab: allowed shifts, guard band, IM separation, how the legs move, plans to return.
Setup tab: allowed shifts, guard band, IM separation, how the legs move, plans to return.
Completed request: headline hits, the optimised pairs sheet, and the remaining direct hits.
Completed request: headline hits, the optimised pairs sheet, and the remaining direct hits.

Overview

Most radio sites do not start dirty. They grow dirty. A network is deployed clean, then a contractor adds two channels, an operations team adds a data channel, an emergency channel is squeezed in for a one off project, and over the course of years the plan accumulates intermodulation products that mask weak signals, shorten range, and trigger intermittent interference that nobody can quite reproduce on demand. By the time the operator notices, the radios are already on the wall, the licences are already issued, and a full redesign would mean recoordinating the whole site.

The noIM₃ Frequency Plan Optimiser solves the problem differently. Instead of redesigning from scratch, the engine takes the existing frequency plan and applies small precision shifts to each channel within hardware tunable steps (typically 6.25, 12.5, 18.75 or 25 kHz) to find the combination that leaves the fewest intermodulation products on the carriers while preserving channel assignments and operational intent. The radios stay where they are. The licence holder keeps the same channel set. The technicians get a CSV reprogramming table and a single field visit to retune. The site comes back online materially cleaner.

Inputs include the existing frequency plan, allowed shift steps, per channel maximum shift limits, guard band requirements, intermodulation separation constraints, a list of channels to avoid, and optional priority weighting so the most critical channels (safety, dispatch, emergency) are constrained to the smallest shifts while less critical channels absorb larger adjustments. Output is a full before and after comparison table, direct and in-band hit counts before and after, the hits that remain with the arithmetic that produces them, alternative plans, before and after spectrum views, an exportable CSV ready to hand to the radio technician, and a one-click hand-off into the Intermodulation Calculator or the Frequency Plan Validator to grade the result.

Capabilities

Constrained shift optimisation

Define the shifts a pair may take (for example ±6.25, ±12.5, ±18.75 or ±25 kHz) and a maximum shift per pair. The engine scores every candidate plan on the products landing on your carriers, direct hits first, then in-band hits, then the least movement. When the plan is small enough every combination is checked and the result is the proven minimum; larger plans are searched by simulated annealing, and the same input always returns the same plan. Guard band and avoid-list constraints are respected at search time, not as an afterthought filter.

Priority weighting per channel

Each frequency pair gets a priority from 1 to 10. Priority 10 fixes a pair in place; 1 to 9 weight how reluctant the optimiser is to move it, so safety, control and emergency channels move last and least while operations, maintenance and data channels absorb the larger adjustments. A maximum shift can also be set per pair in addition to the default.

Before and after comparison table

The primary output is a per pair comparison showing original and optimised downlink and uplink frequencies, the shift on each leg in kHz, the hits before and after, and whether the pair was adjusted. Below it, every product that still lands exactly on a carrier is listed with the expression that produces it, so a hit that cannot be cleared within the allowed shifts is visible as the closed loop of spacings it is. Unchanged pairs confirm which were already well placed.

Side by side spectrum analysis

Two spectrum views, before and after, show how the channel positions move and how intermodulation products shift relative to the carriers. Switching to an alternative plan redraws the after view for that plan.

Headline numbers and alternative plans

Every result reports direct hits before and after (products landing exactly on a carrier centre), in-band hits before and after (products inside a passband, centre plus or minus half the bandwidth), the pairs moved, and whether the plan is the proven minimum or the best found. Ask for more than one plan and the alternatives are returned best first, so a hit or two can be traded for fewer channels reprogrammed.

Surface and underground modes

Surface mode follows RALI LM08 section 6.5.3 and Annex D: the two signal 3rd order (2f1 − f2) and 5th order (3f1 − 2f2) products of the co-sited transmitters, checked against the co-sited receivers, with products that land on a transmit frequency reported separately. Underground mode uses the same rules as the Frequency Coordination tool: every carrier is both a source and a victim, products are 2f1 − f2 and f1 + f2 − f3, and 5th order is omitted because it sits below the noise floor once leaky feeder coupling loss and cascade amplifier IM rejection are counted.

CSV reprogramming export

Export the shown plan as a CSV reprogramming table that maps directly to your radio fleet: label, priority, original and optimised frequencies, the shift on each leg, hits before and after, and whether the pair changed, ready to hand to a radio technician for a single coordinated retune visit. The same plan opens in the Intermodulation Calculator, or saves as a Frequency Plan Validator project, in one click.

Avoid list and guard band enforcement

Frequencies to avoid (incumbent licences, third-party channels) and the guard band are enforced at search time. The optimiser never places a moved carrier onto an avoided frequency or closer than the guard band to another carrier, so the output is deployable as is. A violation already present in the input plan is reported, not created.

Standards & methodology

  • ACMA RALI LM08 section 6.5.3 and Annex D. Intermodulation checks for surface land mobile assignments
  • ITU SM.1446. Intermodulation interference reference
  • ITU SM.337. Frequency separation between adjacent transmissions
  • ACMA spectrum management framework alignment for Australian deployments

When to use this tool

  • Reducing intermodulation on a mine site with a large installed base of UHF repeaters
  • Cleaning up a trunked radio system that has grown beyond its original frequency plan
  • Preparing a reprogramming schedule for a planned radio maintenance shutdown
  • Quantifying intermodulation improvement for a client report before committing to the work
  • Optimising underground radio plans on the 2nd and 3rd order product set
  • Validating that a proposed channel addition does not worsen existing intermodulation
  • Presenting before and after spectrum views to justify a frequency coordination engagement
  • Generating a CSV reprogramming table for radio technicians and field crews
  • Cleaning up emergency services radio plans that have absorbed channel additions over time
  • Resolving intermittent in band interference complaints on operational networks
  • Producing audit grade intermodulation improvement evidence for ACMA compliance reviews
  • Supporting fleetwide channel rationalisation programs without forcing a full redesign

Frequently asked questions

How is this different from the Frequency Coordination Tool?

The Frequency Coordination Tool selects fresh frequency pairs from scratch, which is the right choice for a greenfield deployment. The Frequency Plan Optimiser starts from an existing plan and applies small precision shifts within hardware tunable steps to clean it up without forcing a redesign. Use coordination for new networks. Use the optimiser when the radios are already on the wall.

What shift steps are supported?

Configurable. The presets are ±6.25, ±12.5, ±18.75 and ±25 kHz, matching the tuning resolution of common UHF and VHF radios, and custom values can be added. Staying put is always allowed. The optimiser only proposes shifts from the list, so every returned frequency is achievable on the installed hardware.

How does priority weighting work?

Each frequency pair gets a priority from 1 to 10. Priority 10 fixes the pair in place. 1 to 9 weight how reluctant the optimiser is to move it: between two plans with the same hits, the one that moves high priority pairs less wins. The intent is that safety, dispatch and emergency channels stay put while operations, maintenance and data channels do most of the moving.

Can I see how much improvement to expect?

Yes. Every result reports direct hits before and after, in-band hits before and after, the pairs moved, and whether the plan is the proven minimum or the best found. The remaining direct hits are listed with the arithmetic that produces them. On a 6.25 kHz raster the in-band count has a floor set by how many carriers share the band, because an off-centre product lands on the neighbouring grid point 6.25 kHz away, still inside a 12.5 kHz passband; the direct count is the one shifts can genuinely attack.

Does it support underground systems?

Yes. Underground mode uses the same rules as the Frequency Coordination tool: 3rd order two and three signal products (2f1 − f2 and f1 + f2 − f3) with 5th order omitted, because it sits below the noise floor once leaky feeder coupling loss and cascade amplifier IM rejection are counted. It also drops the TX/RX role filter, because the cable brings transmit and receive into the same level range, and lets you choose whether downlink and uplink carriers mix (cable PIM) or only combine within their own band (a diplexed line amplifier).

What does the CSV export look like?

The CSV contains one row per pair, with the label, priority, original and optimised downlink and uplink frequencies, the shift on each leg in kHz, hits before and after, and whether the pair changed. It is structured so a radio technician can program the new values directly into the fleet without further interpretation. The same plan can also be opened in the Intermodulation Calculator or saved as a Frequency Plan Validator project from the result.

Is the returned plan the best possible one?

When the plan is small enough the server checks every combination of shifts and says so: the result is the proven minimum. Larger plans cannot be enumerated, a dozen pairs with independent legs is already 10²² combinations, so they are searched by simulated annealing under a fixed budget, followed by an exhaustive pass over the few carriers still involved in hits. That result is the best plan found, the page labels it as such, and rerunning the same input returns the same plan.

Can I exclude specific frequencies or ranges?

Yes. The avoid list takes the frequencies a moved carrier must never be placed onto: incumbent licences, third-party channels, anything you do not want the optimiser to consider. It is enforced while searching, so no returned plan puts a shifted carrier within a channel width of one, and the output is deployable as is.

Further reading