Now then TTN’ers! I’ve been reading a lot here about people using higher gain aerials to increase the range at which a gateway can receive messages from a node.
Given that the Ofcom guidance indicates that the max ERP is 25 mW, and given that many of these gateways seem to use a transmitter with an output power of 25 mW without taking into account the aerial, what kind of techniques (if any) are you using to ensure that the effective radiated power of the gateway (transmitter and aerial) remains below the legal max of 25 mW, taking into account an antenna with a gain higher than 2 dBi as explained by @LoRaTracker below ?
Is it better to have a transmitter with less output power and a higher gain aerial, or a transmitter with a higher output power but a lower gain aerial?
I’d be the first to stick my hand up and admit to being an RF newb! There seems to be a decent amount of discussion on this forum as to what is correct and what is not. An easy to understand guide on ERP would probably be really helpful.
Limits in the UK are normally specified as ERP and is the power limt when sent through a dipole.
With a dipole being 2dbi, a 5dbi antenna would have an effective gain for ERP purposes of 3dBm. So you need to drop the transmit power by 3dBm to keep within the limits.
Cable losses can be taken into account, if you lost 1dBm with the antenna cables you would only need to drop transmit power by 2dBm to comply.
So am I right in thinking that it makes more sense to reduce the transmitter power and increase the antenna gain, as gateways will spend more time receiving rather than transmitting?
This is presuming of course that nodes being served by a gateway don’t require downlink from that gateway - which seems the most sensible approach where possible given the duty cycle limits / fair use which reduce the number of downlink messages a gateway can send.
Hi Arjan, I did consider OTAA, but hopefully nodes can be joined at a workshop gateway before being deployed to site. I didn’t think about ADR though, good call!