Cannot connect to a low dbm AP with 5 GHz WiFi interface

I have installed OpenWRT 21.02.3 to TP-Link Archer C6 V2 JP.
With 5 GHz WiFi interface, I could not link to a low dbm AP (approx. 90 dbm).
The AP was seen in scanning list. The connection seemed to be successful.
However, Rx rate stayed 0.0 Mbps (Tx rate became up to several hundred Mbps).
Other equipment, an extender and a USB antenna, can connect the AP.
The 5 GHz interface can connect to middle ~ high dbm access points.
So that, the 5 GHz interface has not failed.

What should I do to connect to low dbm APs?
** I apologize for my poor English.

-90dBm is far too low for a reliable connection. It is also most likely close to the noise floor.

They are probably seeing a higher signal strength.

Depending on the details of your requirements:

  1. relocate your TP-Link so it gets a better signal
  2. swap out the TP-Link for a model that can use a directional high gain external antenna
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Thank you for your quick reply, and detailed explanations.

90 dbm -> -90 dbm.

They are probably seeing a higher signal strength.
Huuum, my Archer C6 and the two equipments were sold in accordance with Japanese radio laws. The extender has only internal antenna, but the Archer C6 has LONG external antenna.

  1. relocate your TP-Link so it gets a better signal
    I have locate all equipments at the same places, in where the signal is best for the AP in my house.
  1. swap out the TP-Link for a model that can use a directional high gain external antenna
    It seems Archer C6 equips with a relatively long antenna among TP link products.
    I will buy an another router, in which OpenWrt can be installed.

That should be true in any country, for that country's laws.
The problem is the received signal strength and that can vary according to many factors. At 5GHz small changes in location can make a large change in signal strength.
Also some devices are more sensitive than others. It is also often the case that a longer antenna is fitted to make the device look cool, when it in fact it degrades sensitivity because the long antenna does not match the frequency (I am not saying TP-Link have done this - I do not know - but it does happen)

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I thought your advice was theoretical.
Wave length (lambda) of 5 GHz is estimated approx. 6 cm.
An appropriate length of antenna is approx. 1.5 or 3 cm (1/4 or 1/2 lambda) ?
However, length of antenna of my TP-Link router is beyond 10 cm !!
This length of antenna is not theoretical (but looks like good, you said).
I think that the length of the antenna is not appropriate.

Of course you do not know what is inside the TP-Link antenna. It might be coil loaded. It might be multiple 1/4 wavelengths to give a better horizontal beam pattern, or it might be just a plain wire....

But none of this changes the fact you have a low signal from the remote access point anyway.

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...and in some cases, the surrounding plastic antenna cover (pipe) is two thirds longer than it needs to be for the actual metal antenna inside, to give the (mere) appearance of bigger antennas (e.g. TP-Link TL-WDR3600/ 4300).

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Yes indeed, that too. A very cool plastic stick /s

If you want to stick with TP-Link, a CPE 710 would be worth looking at. It has a built in "real" high gain directional antenna and is carrier grade rather than domestic grade so the manufacturer cannot get away with any marketing untruths as usually are selling to knowledgeable professionals.


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** I did not know I could attach an image.

The radio wave of Buffalo-A-37D8 (-90 dBm) seems to be received. However, RX rate remains 0.0 Mbit/s.
What does this behavior mean ?

It means the signal strength is far too low for any useful data to be received.

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I understood the signal from the AP didn't have enough S/N ratio.
Thanks for the kindly explanations.