USB extender cable

Can you tell me how long a USB cable can be before the gps signal is lost. 15ft, 20ft?

Standard USB cables are limited to around 16ft total by spec, although you may get by with more I wouldn’t recommend it other than for testing.

You can however go longer with an “active” cable, eg.

I’ve been using a 50’ “active” cable for years without issue.

75’ here, to of the mast to cabin.
Was not a cheap one though.