Signal level to get good DTV

[John]

What sort of signal level is required to get
good DTV quality?

I have a digital antenna with quad shield coax
all the way to the STB. My DGTEC 5000i shows
the quality as 100% and the level as 24dB. I have
read that 20dB is considered the minimum to get
DTV, so 24dB should be OK right. Anyway when I
switch on the STB it always shows "weak signal"
but the picture and audio is always good, no
MPEG artifacts. The only glitch is the STB locks
up from time to time, and I have read a number of
times that the 5000i can do this on signal errors.

So is a 4db margin good or poor? Should I be looking
for a 40dB signal level? I have heard that you can
have too much signal as well and get distortion,
what is "too much"?

Any info appreciated.

--
John Saunders
news1@saunders.id.au