Firstly, what suburb are you in?
Can you see the towers on Mt Dandenong from your roof?
What's the terrain like in your signal path?
All Melb digital channels from the main Mt Dandenong transmitters except SBS are band 3 VHF (SBS is band 4 UHF) so any UHF antenna, homemade or otherwise, will not work for the VHF channels.
ALL antennas should be mounted ON the roof for best results, not in the ceiling.
Older VHF antennas were only designed to receive up to channel 10 analogue, so they do not work well, sometimes not at all, with TEN and ABC digital, which are on channels 11 and 12 respectively.
The phased array design principle in the link is what most commercially-built antennas are based on, but with much better build quality, better specs and reliability.
Mounting location of the antenna can also be critical for digital, as even a few centimetres movement in any direction (incl up/down) can be the difference between reliable reception and no reception in difficult reception areas.
Selection of the correct antenna and it's mounting location are the two most important factors of an installation, then comes cabling, connectors, outlet plates, splitters/taps, amps, flyleads, etc.
If you were in close proximity to a UHF-Only translator, then a homebrew antenna may be ok, but for the main Mt Dandenong TX.... forget it.
USB tuners typically require excellent signal strength and quality (eg: better than what a STB or integrated tuner will work ok with) so you need to start with the right antenna, mount it correctly and use RG6 Quadshield cable (which you have done) use F connectors and F type splitter and fully-shielded outlet plate connectors (I use F to PAL type). You should also use RG Quadshield flyleads.
Your signals will only be as good as the weakest component in the chain and the antenna is the most important part, because if it doesn't capture sufficient signal strength (in digital, it's called channel power) and signal quality (low BER and high MER) then you won't have reliable reception.
Hope this helps
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