Hi,

I think it depends on the model and its intended applications. I use a
"waypoint" only Garmin for hiking that has their new "high sensitivity"
receiver, and it doesn't accept an external antenna. I've yet to use it
in a vehicle where it loses satellites, though in some, it does seem to
be breathing hard to hang onto 'em.

At one time, I believe the Garmin website listed all the accessories
(including external antennae) that would work on a given model. Might be
worth a visit to see if they still provide that kind of info? They also
have the update software available there, though I can't say if that'll
help or not: it may be my imagination, but it seems the first update I
performed DID improve the time to acquire satellites, while the next one
SLOWED things down. However, the readings I get after it, especially for
altitude, have generally improved. It's kind of a crap shoot...

Rick