How to measure a level ( power) of a Wifi signal in a particular place - Page 1
Forum section: electronics / general

author: Jane
author_rank: Frequent Contributor
timestamp: December 14, 2017, 09:03:23 pm
content: Where can I get any useful info about measuring a level ( power) of a Wifi signal? What equipment to use? Network analyzer or spectrum analyzer?What kind of antenna? etc.Thanks

author: mc172
author_rank: Frequent Contributor
timestamp: December 14, 2017, 10:15:32 pm
content: It might be more useful to tell uswhyyou want to know this as it's not quite as straightforward as you might think - definitely not as straightforward as simply measuring the peak signal level on a spectrum analyser with an antenna.Answers range from making a crude 1/4 wave ground plane antenna (for example), rectifying it and sticking it into a moving coil meter, to spending a million quid getting a field strength and reflection plot of your entire house at different polarisations etc.None of this is useful if you are trying to do something in the real world as your device probably has an F antenna printed on a PCB, buried in the device somewhere as generally people prefer shiny glass or metallic-looking plastic to F antennas poking out the side. In which case, for real world results, use a PCB type F antenna, but then you must bear in mind that this doesn't represent absolute field strength.Please elaborate.

author: Jane
author_rank: Frequent Contributor
timestamp: December 15, 2017, 05:55:29 pm
content: Thanks for the reply.I would like to measure a power( level) of an incoming Wi-Fi signal alias wifi AP( access point) and strength/power ( or waveforms) of backscatter signals from that WiFi AP.Do you have any idea what method/measurement device to use?

author: mc172
author_rank: Frequent Contributor
timestamp: December 15, 2017, 07:11:54 pm
content: OK, but for what purpose? What are you going to do with the information?

author: Jane
author_rank: Frequent Contributor
timestamp: December 15, 2017, 08:45:46 pm
content: For my future project I would need to know the backscatter power

author: mc172
author_rank: Frequent Contributor
timestamp: December 15, 2017, 09:52:39 pm
content: I can't really help you unfortunately, sorry. The complexity is quite enormous and you're talking about measuring tiny, tiny amounts of power in a chunk of very congested bandwidth. On top of that you're trying to measure two things at once.To do it, you are going to need at least a network analyser and a spectrum analyser, possibly two spectrum analysers and some pretty clever antennas that you absolutely know the gain vs. bandwidth curves of (you can use a network analyser for this if you have one reference antenna already but you'd need to do it in an anechoic chamber inside a Faraday cage...) as well as the radiation patterns in both horizontal and vertical planes.Then you'd need to do it all over again with your device in place of the expensive reference antenna to characterise your device for real-world performance.Can't you choose another project?

author: Gyro
author_rank: Super Contributor
timestamp: December 15, 2017, 10:18:46 pm
content: I don't know if it would get you anywhere at all but you could try wandering around the antenna with a laptop running inSSIDer, either the free personal version or the trial version of the full inSSIDer Office...https://www.metageek.com/products/inssider/I've no idea how accurate the dBm measurements are (probably dependent on network card), or whether it would give you sufficient resolution, but at least it wouldn't cost anything to try. Presumably the measurements would be affected by the orientation of the laptop antennae but I suppose that will be true of whatever measurement antenna you use.P.S. inSSIDer V2.1 has a much nicer UI

author: retrolefty
author_rank: Super Contributor
timestamp: December 16, 2017, 01:14:58 am
content: I would use an inexpensive RF power level detector based on Analog log amp devices. Such as this ebay item:https://www.ebay.com/itm/1PC-AD8318-RF-1-8000MHz-logarithmic-detector-70dB-RSSI-measurement-power-meter/142140981389?hash=item211843408d:g:mOwAAOSwYIxX9w0v

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2017, 05:30:21 pm
content: Such devices can measure power on a coaxial connection or similar node.However, in free space (or air), "power" itself is meaningless. Normally, one measures field strength in V/m, rather than power in W.