On Mon, 18 Aug 2008 04:54:21 -0700 (PDT), wrote:

If you do want to elevate the antenna for a 3G modem, consider using a
5m long USB extension cable and placing the modem itself high up. It
doesn't give you a directional antenna, but it saves a lot of hassle
with thick low-loss coax.

John

Thanks for your sound advice above, but in this case I'd be attaching it to
a computer which is only a meter below the roof space/slates anyway so
probably not practical to have the modem a few meters higher. I guess I'll
have to try and borrow a 3G phone, take it up to the chimney and see if it
picks up anything.

I wonder if some of the USB modems have a socket for an external antenna.