After a couple of days work I can report that the
Comtech modules won't be of any use to me.
Their LOs are on the high side so the signal will
get inverted. When I looked at them on the spectrum
analyser I noticed that their phase noise is
horrendous even with the synthesiser locked.
Neither of which would be conducive to DVB-T operation.
I suspect I am going to have to build some bespoke hardware.
Looking in my magic box I see I have some 2 GHz ring diode
mixers and some MMICs. I just need to sort out a clean
source of RF in the 700 - 800 MHz range.
Moral to this story folks is don't waste your time putting
your hardware in a box until after you have tested it!
Still I did get to try out some new conical drill bits I bought.