Given a particular link and radio technology, the primary variable components of the link budget are:
- The radio’s transmit power
- The transmit antenna gain
- The receive antenna gain
For this discussion, we’ll ignore other common link budget parameters, such as cable and path losses, since we are looking at power and antenna gain on a particular link.
Most regions restrict a device’s EIRP (Effective Isotropic Radiated Power), which is essentially the radio’s transmit power plus the transmit antenna gain. To comply with EIRP limits, each device must either reduce its radio’s output power, reduce its transmit antenna gain, or both.
Since SkyPilot’s products use high gain antennas, the radio’s output power must be reduced to comply with EIRP limitations. Due to this, there is a common misconception that SkyPilot’s high-gain antennas are not beneficial in EIRP-restricted regions.
However, since the SkyPilot system uses high-gain directional antennas on both transmit and receive, the link budget is still increased due to the antenna gain. Let’s look at an example by comparing two identical links, with different antennas, in a region restricted to 30 dBm EIRP:
- Link 1: radio output power of 24 dBm + transmit antenna gain of 6 dBi + receive antenna gain of 6 dBi = 30 dBm EIRP and comparable link budget of 36 dBm
- Link 2: radio output power of 12 dBm + transmit antenna gain of 18 dBi + receive antenna gain of 18 dBi = 30 dBm EIRP and comparable link budget of 48 dBm
So, even though the use of a high-gain antenna on link 2 resulted in the radio’s output power needing to be turned down by 12 dB in order to meet the 30 dBm EIRP limit, the actual link budget is 12 dB higher than link 1 due to the receive antenna gain. In free-space, this would result in 4 times the range (or an increase in modulation, depending on how you want to spend the link budget).
To put it more simply, EIRP restrictions limit how big your mouth is, but not how big your ear is. And of course there are still the other benefits of using directional antennas, such as causing less interference and being less susceptible to interference.
Tags: antenna, directional, high gain, mesh, synchronous, syncmesh, wifi