Why Ajax 915 MHz Frequency is Superior

915 MHz is drastically better for frequency hopping. While systems like the Hikvision AX PRO or Dahua AirShield use frequency hopping on 433 MHz to get out of trouble, the 915 MHz band gives the hardware a massive playground to hop across.

It comes down to simple math, physics, and Australian law.

1. The Playground Size (Available Bandwidth)

Frequency hopping requires space. If you don't have enough spectrum, you are just hopping back and forth between a few tight, crowded channels.

• The 433 MHz Band: You only have 1.74 MHz of total space ($433.05 \text{ to } 434.79 \text{ MHz}$). Because the window is so tiny, an alarm system can only split it into a handful of channels. If someone turns on a high-powered 433 MHz ham radio or a continuous transmitter nearby, it can easily bleed across and smother that entire 1.74 MHz window, leaving the alarm with nowhere clean to hop.

• The 915 MHz Band: In Australia, the ACMA allocates a massive 13 MHz of total space ($915 \text{ to } 928 \text{ MHz}$). This is roughly 7.5 times more bandwidth than what's available on 433 MHz.

2. Australian Law (ACMA Rules)

The ACMA enforces strict rules for frequency-hopping spread spectrum (FHSS) devices in the 915 MHz band that make it incredibly robust against jamming:

The 20-Channel Rule: To legally transmit at higher power (up to 1 Watt) in the AU915 band, the ACMA mandates that a frequency-hopping system must use a minimum of 20 hopping frequencies.

Because the hardware is legally required to spread its signal across at least 20 widely separated channels, it becomes nearly impossible for normal environmental interference or a cheap, narrow-band jammer to block the signal. The hub and sensors are constantly dancing across a massive spectrum.

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