snip

Have you come across anything useful published by the FCC about
polarisations used for digital terrestrial television.

Chris

Yes. http://www.fcc.gov/mb/video/tvq.html is the start page for most
television queries for US, Canadian and Mexican TV stations. Type
something relevant in the Call Sign block and press Enter. On the
next page, click any of the station's lines and you will next be taken
to a detail page (my term) with many specifics for the station,
commonly including antenna polarization. (You may omit the callsign
and instead enter a city, further downpage. Then, all that city's
licensed stations will be listed and you can bring up detail pages one
at a time.)

Just now, I determined that KTVU is Horizontal and KABC is Circular
(H=V).

Please note that the detail page lists data for every major paper on
file with the FCC (or neighbor government). That is, you find
separate clusters of data for the station as licensed, plus any
construction permits, applications, modifications, etc. Be sure of
what you're seeing, as some of it represents planning that might never
be approved or funded.

Some data will open in a new window; the coverage maps are that way.

Happy hunting,
Sal