Will DAT 75 get to the bottom of poor reception on ITV/C4...?

I've variously heard that 45 dBuV is required for DTT.

However, any thoughts on my original question re the 75 version? I
think it gives about 3dB more gain?

The breakup is less frequent, but drives me mad...

Thanks

wrote:
I've variously heard that 45 dBuV is required for DTT.

Yes, the DTG book (reading further) does talk about adding an unspecified
safety margin to allow of tree foliage, and other variations in received
signal. 10dB seems reasonable.

However, any thoughts on my original question re the 75 version? I
think it gives about 3dB more gain?

No experience, others will have.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

On Mon, 25 Sep 2006 20:05:29 +0100, Mark Carver
wrote:

For noise free analogue reception, most tuner's terminals need to have

Johnny P will be after you for that...

Mark Carver wrote:

According to my DTG pocket book the minimum signal level for reliable
DTT reception is 35 dBuV (again as delivered to the tuner) ?

It sounds as if you're looking at a rather early version of one of the
DTG R-books there Mark. The recommended figure was quickly revised
upwards by 10 dB in the light of practical experience of impulsive
interference.

If II wasn't a problem 30 dBuV would just about be OK, even for 64-QAM,
but in practice II break-ups don't seem to disappear until you're above
40 dBuV - or maybe 50 dBuV with a combination of poorly screened
downlead, isolated outlet plate and crap moulded flylead. Attending to
the latter two as well as the main downlead is quite important.

--
Andy

I live outside the official coverage zone for Sudbury, and have experimented
with a few amplified and unamplified setups.

One thing I would say is that I have never achieved an improvement for
digital TV by using a masthead amplifier.

In terms of forward gain and off-axis rejection, the DAT75 is the best
wideband aerial bar none. Although I still haven't achieved perfect
reception of the ITV channels, the best performance I've ever had comes from
and unamplified DAT75. Be aware that the DAT75 is *big*.

I haven't tried a DAT45, so can't compare them, I'm afraid.

If you don't need a wideband aerial, maybe you'd be better using something
else. Bill and the other experts around here will know what to recommend.

Thack

wrote in message
oups.com...
What's your question Bill?

I don't understand what you mean.

Bill

"Mark Carver" wrote in message
...
harrogate3 wrote:
43dBuV is about 140uV absolute, 39dBuV is less than 100uV.

I may be wrong but didn't the BBC used to consider you to be covered
at 1mV (60dBuV) and fringe at 250uV (48dBuv)? Could just be plain old
lack of signal.

Those figures are for analogue transmissions, and ISTR were contour field
strengths for 'primary' and 'fringe', therefore expressed as dBuV/m ?

For noise free analogue reception, most tuner's terminals need to have
delivered 60 dBuV. According to my DTG pocket book the minimum signal
level for reliable DTT reception is 35 dBuV (again as delivered to the
tuner) ?

Of course carrier to noise ratio has to be considered if there are any
active devices between aerial and tuner for analogue and DTT situations ?

At very low field strengths co-channel interference is often the limiting
factor for DTT reception. Analogue signals that would be far to weak to make
use of can affect DTT a great deal if the DTT signal is very poor.

Bill

wrote in message
ups.com...

I've variously heard that 45 dBuV is required for DTT.

However, any thoughts on my original question re the 75 version? I
think it gives about 3dB more gain?

Ha!

Getting the last little bit of signal out of a big aerial is not easy. Most
times when people take a medium sized aerial down and put a big one up they
end up disappointed.

Another little point. For DTT reception where field strength is poor,
reducing co-channel interference (including any signal/noise on that
channel) by 1dB is often as good as increasing the signal voltage from the
aerial by 1dB. This is the case when co-channel noise is a bigger factor
than receiver or amp noise. So the thing is, use a directional aerial. Large
'high gain' multi-element aerials of a complicated design tend to have
untidy response patterns.

You ain't gonna like this, but where there's a noisy background I can get
far better results on DTT by using a pair of good quality 18 elements or
even logs, stacked or bayed than you'll ever get from a DAT75. Dunnit loadsa
times. This:
http://www.wrightsaerials.tv/025%20s...TC18A%20H.html
knocked the spots off a big high gain aerial (not a DAT75 though).

Bill

wrote in message
oups.com...

Have tried a Tetra notch filter, no difference. All cables are foam
dielectric, double-screened, nickel plated brass screw connection coax
connectors.

Predictions for my OS location are 43 dBuV for Crystal Palace, 39 for
Reigate.

Help...! Thanks in advance!

Why not use a Group A aerial for CP? AFAIK CP is likely to remain Group A even
after analouge switch off.


--

Michael Chare

wrote in message
ups.com...
Thanks folks, yes, it is indeed mounted as per the picture.

I don't know if this is relevant, but the signal 'level' fluctuates on
the ITV channels, but not on the BBC ones at all. (This happens on
either the Sony LCD or my Elgato EyeTV box on my apple mac.)

Where are you?

I wonder if it is something to do with ITV's choice of QAM?


--
MESSAGE ENDS.
John Porcella