If they are looking for analog ABC, it is low band VHF, ch2 to be exact,where the rest are high band VHF, and needs a decent multiband antenna to get it in alot
of areas, well in Brisbane at least. We have Mount Coot-tha
that has a good propagation to most metro areas approx 40km radius, although it starts to get a bit noisy on the ABC due to lowband
interference issues. .
There are many areas of AU that use UHF for TV also. Not enough hills in many parts of the east coast to get the coverage, so there can often be UHF translators that you need to tune onto. I suspect the ABC problem does relate to them not using an antenna that is suited to VHF, saying this of course if they get the other channels (7,9, and 10) ok.
Go here for a more specific channel/frequency guide
to determine if it is the problem by location. ABC is on different channels almost depending on what suburb you are in for some areas. If the DVR
can do digital, then they should go that way as it is now UHF ch21. It may be that they are trying to get analog signals, that will be turned of in the near future... so tuning the system in for UHF propagated
digital is the way to go.
Back in the day when I used to do antenna I recommended the Hills PF11 antenna, multiband 11 element yagi
with low/high band VHF/UHF, or a PF17 (17 element) with mast head amp if they are in a marginalised signal area. But a UHF array is still the best way to go if they can process a digital signal. Hope that helps :)