Best repeater?

My first recommendation is something like this, but see more below.

This is what I "think" you have based on what you said.

1. Your laptop connects to an access point of weak/flaky signal strength.
2. That AP appears to be a router which connects to a modem (to the ISP).
3. You have the passphrase for that AP but not the password for the router.
4. You want a better connection without messing with the router or modem.

While we don't know the frequency range (2.4GHz or 5GHz), or what your

120VAC power considerations are at the location of the laptop, even so it seems to me you have a few options, one of which is the "repeater" you speak of (assuming you can keep it dry & power it up wherever you end up placing it).

That repeater can be almost any extra router you have on your shelves. If you can protect it from the elements and get power to it, that repeater can be positioned roughly about halfway between the laptop and what I'll call the "main router" to act as a wireless repeater.

I have only set up wired repeaters (because the speeds are double that way) but I don't recall that you have to mess with the main router to set up a repeater (but double check that this is a correct assumption). If that's the case then almost any router will work as a wireless repeater and even if the one you have on your shelf doesn't have the firmware to be a wireless repeater, most can be set up with DD-WRT or Tomato or the like which will likely allow wireless repeating.

Another option is to plug in a more powerful transmitter and a more sensitive receiver to your laptop USB or Ethernet port. If you're not LOS and hence bouncing signal it would at least give you more signal to bounce to the main router, and it would pluck out more signal to receive from the main router.

While USB transmitter/receivers are what most people would use to increase the signal strength and receiver sensitivity of a laptop, you may need more powerful & more sensitive professional equipment to plug into your laptop.

A much more powerful transmitter and a more sensitive receiver could be plugged into your laptop's Ethernet port if you have 120VAC power at the laptop location. Almost any access point will work plugged into your laptop Ethernet port which is why that's what I recommend, because you can find powerful ones. I guessed at a few things above so let me know if I guessed wrong.

Good. A store and forward repeater, signal booster, range extender or whatever will work if the endpoints cannot see each other. It's when there are two RF paths, one direct from source to endpoint, and the other going from source to endpoint via a store and forward repeater, that things go awry.

In 2015, I gave a song and dance presentation on mesh networking to the local Linux users group:

Note that a mesh network is nothing more than a repeater, where multiple endpoints can also act as repeaters.

This is what 802.11n throughput looks like going directly from a client radio (bridge) to a wireless access point:

That's what it's suppose to look like. Notice that the 25Mbit/sec to

70Mbit/sec 2.4GHz throughput is quite consistent and stable. The source and endpoint were about 10 ft apart, so there are no signal strength issues involved.

Then, I added a store and forward repeater into the room, located roughly half way between the source and endpoint:

That's what a big problem looks like. The graphs are slower and vary randomly in throughput. The average throughput is 1/2 or less of the throughput without a store and forward repeater. That's expected because the system can allow only one radio transmit at a time which implies that the system needs to send two packets with a repeater instead of one packet without the repeater. The radios are desperately trying to communicate directly in order to obtain the best performance, but are hampered by the repeater which insists on retransmitting almost every packet.

Yet, there are some systems like that which work. The trick is to block the direct path, and have everything go through the repeater. The maximum throughput will still be 1/2 the direct throughput, but the data rate will be quite constant. In other words, reliable but at half speed.

I've had some experience with such installs. On customer in a trailer park wanted to leach off of a nearby coffee shop wi-fi system. Unfortunately, someone put a large brick building in between, blocking the line of sight. Fortunately, the layout was such that I found a place to install a repeater at 90 degrees from each end, so that the repeater could see both end points, but the end points could not see each other. It wasn't as fast as it could theoretically operate, but it was quite reliable. For the curious, yes, I obtained permission to install the repeater from the owner after I offered a small bribe.

Since I don't know anything about the location, equipment, potential interference, etc, I can't offer any specific equipment suggestions. For repeaters, I've been using:

It's not the best but it does have a few advantages. It runs on 5VDC from a microUSB connector, so it can work with a solar powered battery only UPS. It also has several modes besides repeater allowing it to be used as a wireless client bridge at the end of a CAT5 cable. About $40 plus tax and ship:

Note that this is NOT a recommendation for your application.

Ummm... It is better and easier to obtain permission than to obtain forgiveness.

Good luck and think about getting your own ISP service. If you're low income, on some form of public assistance, and can qualify, try these: