Some people are happy running a single AP in their 3,000sq-ft house with the AP in the basement and maybe 4Mbps performance in an upstairs far bedroom. My needs and desires are much higher than that. My guidelines will generally give you very good to excellent performance over that entire floor.
My final thoughts on Hi-Gain antennas and the like...
Hi-Gain antenna's generally don't work..
TL;DR - Science and Physics win!
Here's the reason - everyone is primarily client focused - in other words, if one increases power/gain on the AP, the clients will be better off... sometimes this might work, but testing here, and other sites, generally proves that this ain't true...
We need to be more than just client focused when looking at Tx power and Antenna Gain - an AP is one of many in the WLAN, and, folks know that when running tools like InSSIDer and similar ilk, that a crowed network is a noisy network - and this affects the AP as well as the associated clients.
When a client is transmitting, it's against the background of other noise in the channel - both members of the WLAN, as well as adjacent networks on the same channel (or slightly overlapping channels) - the AP is fighting the same problem, receiving the Tx bursts from the clients...
When we look at the Link - all things are relative - in CDMA 2G speak, we used to call it Ec/Io - or Correlated Signal over Noise - and this is a relative measurement, that's why it is related in Decibels, and not as a hard, fixed value like milliwatts, pascals, etc...
Since this is a relative value - it becomes easy to explain why higher gain antenna's generally don't work very well - they increase the levels of the associated clients, but they also increase the noise of the adjacent WLAN's along with jammers in close channels - so it all becomes relative - and it's generally a net-zero improvement at best.
Where high-gain antenna's can help - we can leverage into the tighter beam patterns afforded by High-Gain antennas and put interfering AP's and Clients into the null of the pattern - this is useful in tall-buildings, where jammers tend to be above and below, but this for many is an edge case... in a typical suburban house in the US, there is no gain, and a possible loss in the event of a house being more than a single floor.
Now going back to 3rd party antennas - those you can find on eBay or Alibaba - my recommendation is stay away from them - here's the reasons why...
In a radio - we do the basic RF modulation - and then we send it over to a power amplifier - this path is controlled by the designer and does not change - from the PA to the antenna - we try very hard to get the right impedance match to the antenna, because it is what converts the conducted to radiated energy - so the entire path is taken into consideration - including ensuring that the radiator has the correct match, and that even with the circuit board traces to the connector to the Reverse SMA on the outside of the router. A mismatch on the Tx side usually results in noise reflected back into the receiver (SWR impact), or lost energy, which is converted to heat...
On the receive side - from the antenna, we go into a low-noise amp - and a mismatch there will generally either reduce the signal, which is never good, or cause saturation and distortion - which is great if your a rock-star guitar player, but not if you're an RF engineer - as will cause issues downstream from the LNA into the baseband, which will not be able to demodulate those saturated/distorted signals...
So again, not a win for big antennas, eh?
End of day - WiFi has a designed link-balance that is pretty much vendor independent - and from there, rate decisions are made - there's a fair amount of "Kentucky windage" to ensure that Tx/Rx levels are fair/balanced, so accept that coverage is what coverage is from vendor to vendor - some do it better than others
Which makes the most important factor of WiFi - planning - put the AP where the people are, and accept that it's not going to get much better..
That being said - there are ways to improve things - AC1900 class routers generally use 3 radio chains, some use 4 - those extra RF chains help quite a bit, and that gain cuts both ways - additionally, the chipsets, using MIMO, and additional features like STBC and LDPC's, increase coding gain, and reduce internal noise - and a 3*3:3 AP is always operating in that mode - even with a single stream client... MIMO rocks, trust me... it's all about coding gain and signal recovery against the background noise.
So - stop tweaking Tx power, it doesn't help - high power AP's generally don't help because they make the link imbalanced, and big antennas amplify everything...
This is probably worth of a blog post on the external site...
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