Free RF calculator
Intermod calculator: 3rd and 5th order products
List every transmitter on the site and this finds the odd-order intermodulation products that fall back near the band, the ones that desense a receiver on the same tower. Add the receive frequencies you need to protect and it shows only the products that land within the guard band of one.
| Product (MHz) | Order | Mix |
|---|---|---|
| 457.7000 | 3rd | 2A-B: 460.1250, 462.5500 |
| 458.6125 | 3rd | A+B-C: 460.1250, 461.0375, 462.5500 |
| 459.2125 | 3rd | 2A-B: 460.1250, 461.0375 |
| 459.5250 | 3rd | 2A-B: 461.0375, 462.5500 |
| 461.6375 | 3rd | A+B-C: 460.1250, 462.5500, 461.0375 |
| 461.9500 | 3rd | 2A-B: 461.0375, 460.1250 |
| 463.4625 | 3rd | A+B-C: 461.0375, 462.5500, 460.1250 |
| 464.0625 | 3rd | 2A-B: 462.5500, 461.0375 |
| 464.9750 | 3rd | 2A-B: 462.5500, 460.1250 |
Runs in your browser; nothing you enter is sent anywhere. The same math the Sentinel RF product uses, tested against it. A planning figure, not an engineering sign-off.
The math
Third order, from two or three transmitters:
2A - B A + B - C
Fifth order, from two to four:
3A - 2B 2A + B - 2C A + B + C - 2D
Sum products such as 2A + B land far out of band and are left out. Products are merged at 1 kHz resolution per order, and the list stops at the lowest 500 by frequency.
Reading the result
A product on a receive frequency is a candidate, not a verdict. Whether it interferes depends on how strongly the signals mix, which depends on where the mixing happens (a transmitter's final, a corroded joint, a fence) and on the isolation between the systems.
Third order products are usually the strongest. A clean list at the orders you checked is worth recording with the site file; a hit is worth a measurement before it is worth a filter.
In Sentinel RF
The site intermod study builds the frequency list for you: click a tower and every licensed land mobile frequency on it loads from the FCC data, along with the FM and TV broadcast stations on the site, which the land mobile database cannot see and which are usually the strongest mixers on the tower. Receive frequencies are derived by band offset and labeled as such, and the report shows where every frequency came from.
Other free calculators
- Coax loss calculatorMatched-line loss by cable, frequency and run length, with connectors.
- ERP and EIRP calculatorERP from power, gain and line loss, or the TX power a licensed ERP allows.
- Fresnel zone calculatorZone radius, 60% clearance and earth bulge at a point on the path, plus knife-edge loss.
- Near-field and far-field calculatorWhere the reactive near field ends and the far field begins, and which one a point is in.
Forty-five calculators, and the FCC data behind them.
The product runs these against real licenses, real towers and real terrain, and prints the result under your operation's name.