My macOS device detects and connects to the wifi signal from a router that is 20 m away. My Windows computer with a USB dongle and my Raspberry Pi can see the signal but cannot connect to it.
Why the difference in range from the different devices?
In the meantime, I set up an old modem as a range extender of sorts.
Answer
Antennas of different size and shape have different gain ratios and different reception patterns.
For example almost all antennas will have a dead-zone. For whip antennas it is a cone originating from the top and bottom of the antenna. Typically this results in a donut or toroidal shaped antenna pattern.
Patch antennas can have a much more directional pattern that "blasts" out in almost every direction from the patch except behind it.
Antenna length affects the gain of the antenna, and in turn high gain antennas have smaller or more focused beams. A high gain whip antenna will be able to transmit and receive further, but will have a much narrower (in the vertical plane) beam and would effectively look like a donut that has been placed flat on a desk and sat on.
The result is that not all antennas are created equal. What you have in your machines may well be different types or formations of antennas. A laptop may well have multiple antennas to increase coverage around it while a simple USB dongle will only have one small patch antenna.
On top of antenna construction there are other factors of the actual Wifi transceiver chip itself that can have a great deal of effect on both the transmitted and recieved signal.
Depending on the wifi module it might have different transmit powers, depending on the region that it was designed for, intended to be used in, or even it's current location (see Wifi Transmission power by country). Power can also vary slightly by component tolerance or calibration. This would lead to subtle differences in output power and whether or not it can be heard by the router.
Transceivers may also be slightly more or less sensitive and as a result have a higher or lower error rate necessitating packet retransmission and/or making a connection unreliable.
Some wifi modules also support multiple antennas (giving overall better coverage) and be able to perform beamforming whereby signals are transmitted at tiny delays over multiple antennae in order that the signal interfere with itself in a way that is beneficial and provides constructive interference and therefore better signal at specific zones (i.e. your router).
There can also be local electromagnetic interference from electronics such as the laptop or Raspberry Pi that the wifi dongle is plugged into. Cordless phones (that have a base station plugged into a landline) also operate in the same free frequency bands as Wifi, as do Bluetooth devices and many other wireless toys and devices. Microwave ovens also operate at a similar frequency, so one with poor shielding could cause interference.
Then there is also different frequency bands. Wifi used to primarily operate at 2.4Ghz, with just a few 5GHz devices. Now that there are so many devices in the 2.4GHz area the 5GHz band has become more desirable. The 5GHz band has a problem in that the higher frequency is also blocked more by walls, objects and has a higher atmospheric attenuation. Which band your Wifi is using can affect reception due to range, other devices and general local electronic and/or environmental interference.
There is no simple way to say why one device will work and another won't. It depends on a lot of factors both in your specific device and local area.
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