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Slow 5ghz on RT-AC68U

Discussion in 'Asuswrt-Merlin' started by Grahammcm1888, Feb 20, 2019.

  1. Grahammcm1888

    Grahammcm1888 New Around Here

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    Hi. I am experienceing slow 5ghz speeds on my RT-ac68u. My iPhone and android tablet max out around 120Mbps when connecting to the RT. Yesterday I purchased a RP-ac68u and placed this in the other side of the house.
    when my devices connect to the RP I get expected speeds , maxing at around 700Mbps+ . Presumably the link between the RT and the RP is good ? I can't work this out. I don't want to return to stock firmware. Running 384.9. Spot 1 is RT and spot 2 is RP (which is low at time of capture).
     

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  2. Mutzli

    Mutzli Regular Contributor

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    Check the wireless settings. Universal Beamforming should be disabled as well as Airtime Fairness on both the 2.4 and 5GHz channels. Choose a fixed channel for the Channel Bandwidth. Try 20MHz only on the 2.4GHz channel and a fixed control channel that has no interference (Check with WiFi Site Survey). For the 5GHz choose 20/40MHz and a control channel above 153 to avoid DFS channels
     
  3. ColinTaylor

    ColinTaylor Part of the Furniture

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    Choosing 20/40MHz will halve the theoretical maximum speed (to 600Mbps or less depending on the client), so I'd suggest he leave it on 20/40/80MHz. As the OP is in Glasgow (not the US) he doesn't have access to channels over 140. So to avoid using the DFS channels I'd suggest you choose a Control Channel between 36 and 48 (even if your neighbours are using the same channels).
     
    Last edited: Feb 21, 2019
  4. EmeraldDeer

    EmeraldDeer Senior Member

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    My 5 GHz devices support 80 MHz so I have 80 MHz only selected.
    I am not sure how 20/40/80 behaves. If a device only supported 20, would the bandwidth be just 20 MHz, in which peaking at 120 Mbps would make sense?
     
  5. Mutzli

    Mutzli Regular Contributor

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    Sorry, I thought the ac68u supports 20/40 only.
     
  6. Grahammcm1888

    Grahammcm1888 New Around Here

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    Thanks for the tips so far guys. To be honest I have tried quite a lot of the suggestions posted above. I have even tried changing the power supply to the router which made no difference.
    I have tried a lot of 5Ghz channels but it does not make any difference so usually I resort to putting it back to Auto. I have also tried setting the 5Ghz channel to 80 MHz only but the problem persist. I am wondering if I should try a factory reset (never done that since changing to Merlin) ? If I do proceed with this can I just flash the latest version of the firmware to the router without having to do incremental version upgrades ? I am kinda clutching at straws and I am not ruling out a faulty router yet. The speeds received from the RP may be a red herring as the purpose of the RP is to amplify what is being received from the RT but to contradict this , on the RT web-page the link speed rate on the received 5GHz are consistent with what is being received on the mobile devices. I have attached screenshots of some results I had from this morning showing (again) Spot 1 as the RT and RP . Also attached is a photo showing the dramatic increase when moving from RT to RP. Also attached are settings from router , just in case I have missed something obvious.
    Thanks again.
     

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  7. ColinTaylor

    ColinTaylor Part of the Furniture

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    Yes! You should absolutely do this if you've never done it before (or for a long time). There have been quite a few changes to the wireless software that seem to require a factory reset to sort out.

    The factory reset doesn't change or revert the firmware version. You will still be running 384.9. What it does is reset all the options (including hidden low-level settings) to their default values. After doing this you will have to manually setup your router again. Do not reload a "save settings" backup file as that would negate the purpose of the factory reset.
     
    Grahammcm1888 likes this.
  8. Grahammcm1888

    Grahammcm1888 New Around Here

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    Understood, I will give this a go when the kids are out / off Xbox's. I don't want world war 3 to break out :)

    It really shouldn't be too much of a problem entering in the details as I have really only Wifi ,Wan and some VPN settings to enter in (I think!)
     
    Last edited: Feb 21, 2019
    QuikSilver likes this.
  9. ColinTaylor

    ColinTaylor Part of the Furniture

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    This is what mobile phone cameras were invented for. :D
     
  10. L&LD

    L&LD Part of the Furniture

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    When changing from Asus 'official' to RMerlin's firmware or vice-versa, a reset to factory defaults followed by a minimal and manual configuration is a requirement. When you're experiencing anything out of the norm, like the issues here, it is your first step to get your network to a good/known state so that any real troubleshooting can begin to happen. Otherwise, you're just randomly switching settings until it seems you got it to work again.

    The links in my signature should be a good starting point.
     
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  11. ColinTaylor

    ColinTaylor Part of the Furniture

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    Not strictly true. It's not always required, but very often is. That said, there are so many scenarios where it is required that it's not worth risking not doing a factory reset.
    https://github.com/RMerl/asuswrt-merlin/wiki/Installation
     
  12. L&LD

    L&LD Part of the Furniture

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    ColinTaylor, you are contradicting yourself (I think). The first point makes it clear to do a factory reset.

    The second point addresses the case of staying within RMerlin's firmwares and going from one version to another. ;)
     
  13. ColinTaylor

    ColinTaylor Part of the Furniture

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    TBH I'm just playing devil's advocate :D.

    Given that these are instructions for installing Merlin for the first time, my interpretation of the first statement is that it applies to those people that are currently running neither stock Asus firmware (Asuswrt) nor Merlin. i.e. users of DD-WRT, Tomato, etc.

    The second sentence is slightly more ambiguous, but I believe could still be applied to moving from stock firmware to Merlin. It was written in 2012 when Merlin used the same version numbering as Asus. Back then if you went from stock version 3.0.0.3.178 to Merlin's 3.0.0.3.178.15 a reset was not necessary because there were no significant differences in the code base. Of course whether that principle is still true over 6 years later....

    On the other hand, what with all the closed source components, and the way Merlin has to assemble some firmwares out of the "bits" of others, it would be foolish not to do a factory reset. :)
     
    Last edited: Feb 21, 2019
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  14. Grahammcm1888

    Grahammcm1888 New Around Here

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    I have given the factory reset a go and the 5Ghz rate went back to where it should be , so that is a success. I did start putting the settings back in and noticed that the 5Ghz speed dropped back down again. So I factory defaulted again. I am not sure what setting(s) caused the issue so I am leaving it with the bare minimum settings at the moment. Only WAN , LAN, WIFI and DDNS setup at the moment and it seems fairly solid (500Mbps+). I will give the VPN , USB apps, VPN, etc settings a go tomorrow and monitor the performance of the 5Ghz RT performance in the meantime.
    Getting there , thanks again :)
     
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  15. ColinTaylor

    ColinTaylor Part of the Furniture

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    Bear in mind that anything that disables or bypasses the router's hardware acceleration will have a significant negative impact on internet speeds. So that's things like QoS, IPTraffic and VPN. You can check that status at Tools > System Information > Network.
     
    Grahammcm1888 likes this.
  16. Grahammcm1888

    Grahammcm1888 New Around Here

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    I thought that might be the case but 5Ghz wifi speed seems strange?


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