Can Asus RT-AC58U/ACRH13 do 'Non-WDS-Bridging mode' with OpenWrt?

WiFi on my PC & devices is just a little out of range of a free WiFi internat access spot I want to connect to. I have used my phone as a RF modem to my miniPC via USB as it can just reach on a good day. However the phone cannot at same time act as a hotspot so other local device can access internet at same time. I want to get a) a stronger link to the remote 2.4GHz Access Point, and b) make a 5GHz local hotspot, so my local devices can connect without cables.
I was told any main brand Router caan do this. As my PC is a NUC taking very little power, I bought a Asus AC58U on account of its 4 x 5dBi Antenna indicating long range, and its low ~5W consumption. Unfortunately I found it would not act in Router mode with the remote Access Point replacing the ADSL wire input, a limitation I discovered of AsusWRT. All I was able to confirm was the AC58U could 'see' many more APs than my phone, implying its hardware was sensitive enough to reach the Remote AP I want to connect to.

I then learn't 2 things, smallnetworkbuilder article explained I needed the 'Non-WDS-Bridging mode'. I read the 'full version' of OpenWRT can do that, and recently the AC58U was added to your mainline support.

So my first question is if I install the OpenWRT image(s) specified for the AC58U, will I be able to fairly easily configure it in 'Non-WDS-Bridging mode' so its connection to the Internet is via the Remote AP ?

If answer to above is yes, my 2nd question is can it simultaneously operate as a 'Hotspot' so my NUC & other low-power devices can also access internet via the AC58U ?

Should be clear from above I am a noob re. Routers. I remember flashing BIOS ok a few decades ago in days of tower PCs, but am not familiar with replacing Router firmware. The TOH>AC58U lists 5 'image files'. Do I need to flash all 5 of them, if so is there a instruction guide describing the procedure. (I looked inside the Router and spotted the serial 4 pinholes. I bought a USB 'FTDI232' converter some time ago (intended for programming a ESP8266 then) with 6 pins. It has both 5V and 3.3V pins. Am I right in thinking I should connect only Gnd, Rx, Tx, and 3.3Vcc to the AC58U ?

If the answer to 1st question is no, then can someone recommend another _'long Wifi range, low consumption, low-medium cost Router' (AC1200 is fast enough) readily available in UK that will achieve above objective ?

Almost any OpenWrt chipset (depending on the capabilities of the wireless chipset to operate both STA and AP mode on the same radio) can act as client (STA/ managed) for another wireless network, it can also act as router (NAT) and AP towards your internal network and devices. What it can't do, given that plain IEEE 802.11 doesn't specify this functionality without non-standard extensions (like WDS/ 4addr), would be transparently extending the remote network (without its cooperation of providing WDS/ 4addr functionality). This means the remote network will only 'see' your AP client interface being connected to its bssid, but your internal devices won't be able to get their own IPs within the upstream IP range and have to rely on NAT instead.

ath10k/ ath10k-ct as used in the rt-ac58u (ipq40xx) should concurrently support one STA interface plus multiple AP interfaces, the limitations are that (obviously) the radio being shared for STA and AP networks can only work on a single channel (the one mandated by the remote bssid you're connecting to in STA mode) and that the corresponding AP interface only comes up after the STA interface has connected successfully.

I don't have an AC58U, but I'll try my best.

Do not connect anything to the router's 3.3V pin.
Set up your USB-serial converter to use 3.3V output level.
Connect GND to GND, and cross over the data lines (Rx to Tx, Tx to Rx).
The wiki also has instructions on using the serial port.

You need two images: initramfs and squashfs. They are available from either the stable version (18.06.1) or the development version (snapshot) of OpenWrt. Try stable first.

The initramfs image will be booted as a temporary operating system for the flashing procedure, quite like a bootable DOS floppy disk with the BIOS flashing tool in the old times.
The squashfs image will be written to the flash storage; it is booted after the flashing is complete.

Here are the instructions for flashing the AC58U.

Thanks for your help. I think I understand partially in that: the OpenWRT image for ac58u is a 'full-function OpenWRT', the remote AP just sees my ac58u simply as a client; that the ac58u can also, - simultaneously - act as an AP, but here I don't understand... must use NAT to connect to the stream used in ac58u client mode. - I have no control over the remote AP, but, I assume, can at least determine the upstream IP range, and thus then define the IP range of the ac58u AP mode to be the same. Will this allow devices conneced to my AP to access the internet ?

Somewhere I read if it is the 'same radio' acting "simultaneously" (being 'shared' I guess more like half-duplex) as Client & AP, the throughput will be halved. But as the ac58u has 1 radio for 2.4GHz and a separate radio chip for 5GHz, would that degradation not apply ?

At a minimum, would installing OpenWRT on the ac58u in Client mode allow my PC to access the internet via the remote AP using a ethernet cable to one of the ac58u LAN ports ? (almost like previous configuration where my phone connects to the remote AP, and my PC connected via USB to my phone sees same stream)

Many thanks for your helpful advice and 2 links. Before replying I tried revisiting TOH>AC58U page where I saw 5 image files listed, but found a page ..toh/asus/rt-ac58u that looks very different. If I understand your advice correctly, in short, I need to initially flash a small 'initramfs' bootstrap program, I guess living in RAM, then the final full program called 'squashfs' to flash storage ?
Edit: now found the link to where I saw 5 image files listed: ...toh/hwdata/asus/asus_rt-ac58u - but as you explain snaphots not fully tested - avoid the last 3 files.

Read Serial port instructions in your link - very clear thanks. I will need help with the AC58U Flashing instructions dated 7 March which list many type .bin files to upload, not mentioned in other documentation. It also contains many types of commands like ssh, scp that are new to me, must learn how to use, I guess all done in a DOS like command line environment.

Reason for joining OpenWRT Forum now, is I need to know if my objective of getting a stronger link to the remote AP achieve using OpanWRT on existing AC58U, or best done buying a cheapish AC1200 Router better fitting objective while still in UK, as it is at my destintion I need the strong link to a remote AP. Reply from 'slh' seems to answer my question 1, yes I can, or at least no further forward by changing hardware. I see Forum threads autoclose after 10 days inactivity so guess will need to open my enquiry afresh to get help on the 7 March instructions as it may be about 6 weeks before I settle at far end.

There are only the two image files, initramfs and squashfs. The instructions use a simplified filename of the squashfs image, and they do mention the initramfs image, but without a filename.

Maybe you got confused by the list of changed files at the end? The flashing instructions are part of a commit message, which is a description of the code change that brought AC58U support into OpenWrt. If you are not a developer, you can stop reading after This will will automatically reboot the router.

The ssh and scp commands are meant to be run on a Linux system; suitable Windows tools would be putty and winscp. In addition, you need to set up a TFTP server and know how to configure your network interface with a static IP address.

The autoclose can be triggered manually by a moderator, or automatically when someone marks an answer as a solution. Any other threads should stay open indefinitely.

Once you get OpenWrt installed, you want to set up a routed client configuration.

This works just like the usual default configuration where wired and wireless users are in the LAN, when they go to the Internet they are NATed to the single IP of the WAN. Ordinarily that is a wired connection to a cable modem etc; all that you need to change is to make it a wireless client of the public AP instead.

When NAT between two networks, they have to have different IP ranges. Set your LAN to be outside the IP subnet you get from the AP, or it will not work.

Thank you for your helpful advice which will come in very useful once I have installed OpenWRT. It appears from Slh's and your posts the AC58U will achieve my objective. I had thought I might have to use a dedicated type of 'client only' range extender (not the type for filling in deadspots in your house) requiring connection only to a PC, a 1 trick device, unable to connect to other types of local devices.

Am preparing for travels. It will be near 6 weeks before I can put much time into this once I arrive at far end. As I am a novice at Routers, think I should take it in easy stages, and first learn how to do the initial steps in the 'Instructions for flashing the AC58U' (dated 7 March) In that document, the 1st Sect 3 "set your PC's IPv4 Address to". Will this interfer with the 'USB Tethering' I need for my PC to access the Internet via my phone, or is it easy to restore PC to previous IP setting ?

In sect 4 "...upload the initramfs image." - is that the file in URL , and do I use WinPuTTY to copy over ? Have installed WinPuTTY, but no experience using it. I read an article comparing PuTTY and 'winscp'. Am I right in thinking my interaction with winscp to do the actual secure copy is entirely by sending command lines through PuTTY ?

In 'Instructions' 2nd sect.3 I will need spoon feeding steps '3.1' to '3.4'. For example "Copy over the openwrt-sysupgrad.bin image to router's temp directory" is that the 4.6MB file in URL ?

Is it possible to practice a dummy run of each of the commands in the 'Instructions' without actually altering the Router ?

Thank you also for your advice on future steps once I get OpenWRT installed - hopefully by early December when I should have a serial cable and access to fine-tipped soldering iron.