I am using a Garmin GNC 300 XL in my under construction RV-7A and I am in need of a GPS antenna. In tests, the antenna I have for the Garmin 90 brings up a picture, but I don't know about refresh rates, etc. Will it work as well in flight? Perhaps someone knows of a Mouser replacement for same? I will be mounting on the glareshield, so I don't think that weather or heat is a factor. Or, does anyone have a cheap replacement? I am just looking for alternatives. Thanks.
 
If you plan to use the 300 for IFR then you need to use one of the antennas specified in the 300's installation manual.