In article ,
Jim K wrote:
do they exist and what are they called please?

I want to link a distant pc without a wireless card to my home network
using network cable connected into a wifi "repeater" as it were - i
already have a wifi router at the base "end".

You're after a Wi-Fi Client Bidge device. Box with antennae and an
Ethernet socket. Gives the abiltiy to plug one (or more) devices into it.
Some standalone access points can work in this mode.

I use Draytek AP700's for this purpose. They're about £60 depending on
where you buy. (I'm a Draytek dealer so get them direct)

Could the signal be made directional from such an extension? to limit
potential for snooping (yes I have usual encryption in place already)

You can get directional units, but they're much more expensive - yupically
you might look for something with a flat-plate antenna rather than the
usual stubby omnis, but you'll still be at the mercy of reflections, etc.
Better to run a VPN over the Wi-Fi link if you're that paranoid.

Gordon