can i use my airport express as a stand alone signal booster

Without knowing more about what you are trying to do with the AirPort Express base station, it would be difficult to give you an exact answer.

All we know is that you are asking can the AirPort Express be used to "boost" a Wi-Fi signal. The answer is "no." That's because when used for this purpose, the Express can only extend the Wi-Fi signal at the same bandwidth that it receives the signal. If you mean can it make the signal stronger, the answer could be "yes."

Not sure what you mean by "stand alone" WiFi booster. The Express has to "boost" the signal that is being provided by another WiFi router, so the Express cannot repeat the wireless signal if it is the only wireless device on the network.

If by "stand alone", you mean that the Express will be "boosting" or "repeating" the WiFi signal that is being provided by another WiFi router.......the Express can do this wirelessly.....IF.....your main router is also another Apple AirPort router.

If your main router is a third party router provided by another manufacturer, the Express will not be able to wirelessly "repeat", or "extend". or "boost" the WiFi signal. This is because Apple uses a proprietary system that is designed to only work with other Apple AirPort routers.

Please see my post just above for the answer.

You can use the AirPort Express as a signal extender......IF.....the "main" router back at the headquarters broadcasting the WiFi signal is another Apple AirPort router.

Is it? Probably not, but anything is possible.

If you had two AirPort Expresses, you could configure one to "join" the WiFi network provided by the campground, then connect an Ethernet cable from the "joining" Express to a second Express, which you set up to create your own private WiFi network.

Upsides....a much stronger signal and more security. Downsides.....you have to buy another Express if you don't have one.

This is the setup that I use when I'm traveling and the hotel only provides a WiFi connection. Works great. I can connect all my WiFi devices to my own password protected private network this way.

If your Mac has an Ethernet port, you could go ahead and set up the Express that you now have to make sure that it will "join" the network correctly......before.....you purchase another Express.

See if the following article can help answer that question:

Best WiFi Booster for an RV! - YourFullTimeRVLiving

Good suggestion from Tesserax as well.