My guess would be that the computer will look for whatever signal is strongest. That shouldn't be a problem. Do you have a means of determining which signal is better...the built-in or the external antenna? I'd be surprised if the difference is more than marginal. Are you having problems using the built-in antenna?l

If by "wifi antenna" you mean a USB-connecting dongle that's a Wifi NIC (network interface card), then my suggestion is Yes. Do disable one so you don't have two active at the same time.

I wouldn't liken having two active network connections to having two security programs running.

ainoh, The external antenna is a much stronger signal. No buffering.

Elmer J Fudd, Let me give an example in another form using Public. If I were to go to an RV park that has free WiFi, but the signal is very weak, and by plugging in the external USB antenna, it showing up in number 2 ID list, where the signal has like 4 bars opposed to 1, then I would click on that one which has more bars than what shows with the internal WiFi.

You didn't answer my question - are you talking about an antenna, or a USB Wifi NIC?

Same answer as before - if you're talking about having two NICs active at the same time, disable one.

I believe it's something like this Crane Antenna that she is using Elmer.

Elmer J Fudd, I am sorry, I meant to, and forgot to add this: Wireless antenna

Thank you Mike. I didn't see that. It pays to read, huh? (My pet peeve)

Sorry (Elmer), I forgot to give Elmer J Fudd the link in my answer to him above, to help him know what I was using.

Yes, Mike has it and also with the clarification. This is an USB external Wifi NIC that uses a high gain long distance antenna. It's a NIC. This particular item seems an odd choice to use in a house because these are more intended to use with a distant outbuilding or other areas (like an outside area) where your in-house Wifi signal is weak. Or, if you're using (with or without permission) a neighbor's internet connection.

A better and more convenient approach (that would accommodate multiple devices) would be to use a repeater setup, which can be done several different ways. Repeaters rarely need a high gain antenna.

No matter what approach is done, it's better that only one NIC be active at one time on any device. The second should be disabled, as I said before.

I got the impression that the Crane product was for use in an RV park where WiFi reception is poor. There it would be a good choice, especially if it could be positioned outside of the RV.

Now if I'm misunderstanding the intended usage and it is for a home, say, where the router is located some distance away from the computer, then there a probably better choices. Some type of repeater, powerline adapter, or even running Ethernet cable.

I don't know anything about RV parks but urlee said in the first post that this is for a desktop tower. So, likely use is in home. You (mike) and I have both described more common alternatives and why. But the OP has what they have and if it works, fine.