The onwer of Shark Byte has said that by changing the 5.8ghz video signal from 720p 60fps to 720p 30fps, the bandwidth is halved. I get that. But he is saying that the range and penetration is better.
Unless they are doing some magic, I can’t see how that is true?
If you half the receiver bandwidth you also half the receiver noise. So effectively you increase the signal to noise ratio. Wifi does this by dropping data rate depending upon signal. With a very small bandwidth and very low data rate range can be mind boggling…Voyager space probes.
For both analog and digital signals reducing the bandwidth increases the signal to noise ratio for a given fixed power. The cost to this is that less information over time can be sent in a smaller bandwidth.
A standard 2.4GHz RC controller has an effective radiated power of 100milliWatts or 20dBm (60milliwatts from the TX module to dipole antenna which has 2.15dB of gain over the theoretical isotropic radiator). The data being sent is usually 12bits per frame or more. The more bits/frame the greater the resolution.
The telemetry from the receiver on the model is transmitted at close to 20milliwatts, or 13dBm, and usually into a simple 1/4wave antenna with no gain. Due to the the type of info being sent this can be conveyed in an 8bit frame or less, which results in less bandwidth being used, but can still maintain the same distance and penetration as that of the control link.
The above example also explains why Express LRS can surpass the range of ImmersionRC Ghost. IRC Ghost uses 12bits/frame for the control link and can support up to 12channels, with the eight auxiliary channels using a lower bit rate of 8bits/frame. Express LRS uses 8bits/frame for the first four channels (AETR) but uses 3bits/frame (I believe) for the three auxiliary channels available.
The end result is the bandwidth of ELRS is smaller than that used by Ghost so it has the ability to work at much lower noise levels, even though both systems are employing the same LoRa techniques. Something like -140dBm compared to the -120dBm of Ghost.