# Range of wireless signals

I've put up this question already on physics.SE but I miss an answer to the following:

My assumption: A 5 GHz band provides a higher bandwidth and therefore is more stable as it can support more users compared to a 2.4 GHz band. But the latter has a higher range and can be considered more stable in this aspect. Hence, I've read that the Intel wigig is a 60 GHz band but supports only a range of 10 m.

I would like to know two things: The bandwidth is not the frequency, right? Why can the 5 GHz band support more participants than the 2.4 GHz? Furthermore: How is the possible range connected to the frequency?

It is an oversimplification to say lower frequencies have longer range. See Is free space path loss dependent on frequency? It's more accurate to say the range of a half-wave dipole decreases as frequency increases. But then so too does the size: a tiny half-wave dipole simply intercept less energy. Solution: antenna arrays, which become increasingly feasible as frequency increases.

Bandwidth is not frequency. Bandwidth is the difference between the lowest frequency and the highest frequency used by a radio signal.

There's another sense of "bandwidth" for digital communications: it's how fast bits can be sent. The two are related by the Shannon-Hartley theorem. Another variable in the Shannon-Hartley theorem is the signal-to-noise ratio. This is another thing limiting the range of WiGig: to achieve those high speeds requires a very good signal. Signal quality diminishes with distance as the radio signal spreads out due to the inverse square law.

Higher frequencies generally support higher bandwidth simply because there are more possible frequencies at high frequency. Are there more 5-digit numbers or 20-digit numbers?

For a real example, the amateur 40 meter band goes from 0.0070 to 0.0073 GHz in the US. Thus the bandwidth of the entire band is 0.0003 GHz. Since the entire band must support multiple users, the bandwidth of an individual signal is much less, typically 0.000004 GHz or less.

By comparison, the 23 centimeter band goes from 1.24 to 1.3 GHz, and so is 0.06 GHz wide. This makes it 200 times bigger than the 40 meter band.

A WiGig channel is 2.16 GHz wide, whereas WiFi is 0.02, 0.04, or 0.08 GHz wide. That makes the WiGig channel too wide to even fit in the same 2.4 and 5 GHz allocations used by WiFi, so the only option is to go higher in frequency, where there's room.

• I think by "longer range" he's referring to the fact that 2.4GHz isn't as eagerly absorbed (by walls, trees, random black labradors, etc) as 5GHz, so while it won't go farther, it's easier to go farther. Aug 16, 2018 at 14:00
• "It's more accurate to say the range of a half-wave dipole decreases with frequency. But then so too does the size". It would seem that the sense of both of these statements is backwards. The effective aperture of a 1/2 wave dipole increases as frequency decreases and the size increases as frequency decreases. Perhaps you were thinking wavelengths while writing frequency? Aug 16, 2018 at 14:35
• @GlennW9IQ corrected, thanks Aug 16, 2018 at 15:43
• The antenna stuff seems less relevant to the OP's question compared to absorption (including building material affects) — maybe you could address that more? For the frequencies in question en.wikipedia.org/wiki/Radio_propagation#Absorption says "As the frequency rises, absorption effects become more important. At microwave or higher frequencies, absorption by molecular resonances in the atmosphere (mostly from water, H2O and oxygen, O2) is a major factor in radio propagation." Aug 16, 2018 at 19:53
• At first, thanks a lot! I read it (several times :) and also the cited already answered questions which were mentioned. I have a good feeling now to dive into it more - and I will - but nevertheless: What makes the WiGig signal finally so weak (or short)? Why can't it travel through walls and why are there only a few channels supported with it (e.g. from 2 in China, 3 in USA up to 4 in Europe)?
– Ben
Sep 19, 2018 at 9:07