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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

Just a reminder about the sensitivity of modern DTT boxes



 
 
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  #11  
Old November 21st 13, 10:54 AM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default Just a reminder about the sensitivity of modern DTT boxes


"Bill Wright" wrote in message
...
I've been setting up some Humax boxes in the workshop. I wanted to use the
raw Emley Moor aerial feed because there's a fault on the RF system that I
haven't got round to fixing. The raw feed has no filters. Bilsdale comes
in with very uneven muxes at around -6dBmV. I attenuated the feed by 30dB
and the boxes were still tuning Bilsdale, and reception was perfect.
That's ridiculous.

Bill


Are you sure there is not a repeater?


  #12  
Old November 21st 13, 10:56 AM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default Just a reminder about the sensitivity of modern DTT boxes


"tony sayer" wrote in message
...
In article , Woody
scribeth thus
"Mark Carver" wrote in message
...
Woody wrote:
that when we have effectively increased the Tx power by about
4dB in DSO.

We did ? it might have been +4dB, but how is that figure of 4dB
arrived at ?



Well its actually as a result of the nature of the signal and how
it is measured.

In analogue the Tx output power was only ever achieved on peak
black, but as it was AM the average level was way below peak,
typically 10dB or more. The received signal strength would thus
tend to be read from this average level. Thus Emley for instance
whilst a rated erp or 870KW per channel the average level that
gave the receiver signal strength was more like 87KW or less.

With a COFDM the amplitude registers as essentially constant at
or near peak level, so the signal strength reads that level. The
rated erp of Emley on DTTV is 174KW, which is as far as the tuner
is concerned at least 3dB higher than it was using before.

At least that is as I understand it but of course I may be well
wrong and am prepared to be corrected. :-))



Agree with that in general.,.

It does seem that reception on DTV these days is better, least I can
receive DTV signals usually ones out in the office on a simple indoor
aerial whereas I could not do that before on analogue...


That is to do with reflections and image rejection. On analogue if you
lived near flats or a cliff you would get ghosting.


--
Tony Sayer



  #13  
Old November 21st 13, 01:08 PM posted to uk.tech.digital-tv
Woody[_5_]
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Posts: 1,820
Default Just a reminder about the sensitivity of modern DTT boxes

"R. Mark Clayton" wrote in message
...

"Bill Wright" wrote in message
...
I've been setting up some Humax boxes in the workshop. I
wanted to use the raw Emley Moor aerial feed because there's a
fault on the RF system that I haven't got round to fixing. The
raw feed has no filters. Bilsdale comes in with very uneven
muxes at around -6dBmV. I attenuated the feed by 30dB and the
boxes were still tuning Bilsdale, and reception was perfect.
That's ridiculous.

Bill


Are you sure there is not a repeater?



Bilsdale only has a few repeaters and they are all up the Dales
or on the coast. Remember that since DSO there have been problems
with Bilsdale reception much much further south than sunny
Rotherham - Coventry springs to mind.


--
Woody

harrogate three at ntlworld dot com


  #14  
Old November 21st 13, 02:45 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
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Posts: 9,381
Default Just a reminder about the sensitivity of modern DTT boxes

R. Mark Clayton wrote:
"Bill Wright" wrote in message
...
I've been setting up some Humax boxes in the workshop. I wanted to use the
raw Emley Moor aerial feed because there's a fault on the RF system that I
haven't got round to fixing. The raw feed has no filters. Bilsdale comes
in with very uneven muxes at around -6dBmV. I attenuated the feed by 30dB
and the boxes were still tuning Bilsdale, and reception was perfect.
That's ridiculous.

Bill


Are you sure there is not a repeater?



It was the mux carrying BBC NE on the correct channel for Bilsdale. The
only signals visible when I scan the output of the Emley aerial are
Emley and Bilsdale. The aerial is screened from most directions. It's in
the back yard, not on the roof.
Bill
  #15  
Old November 21st 13, 04:19 PM posted to uk.tech.digital-tv
R. Mark Clayton
external usenet poster
 
Posts: 1,331
Default Just a reminder about the sensitivity of modern DTT boxes


"Bill Wright" wrote in message
...
R. Mark Clayton wrote:
"Bill Wright" wrote in message
...
I've been setting up some Humax boxes in the workshop. I wanted to use
the raw Emley Moor aerial feed because there's a fault on the RF system
that I haven't got round to fixing. The raw feed has no filters.
Bilsdale comes in with very uneven muxes at around -6dBmV. I attenuated
the feed by 30dB and the boxes were still tuning Bilsdale, and reception
was perfect. That's ridiculous.

Bill


Are you sure there is not a repeater?


It was the mux carrying BBC NE on the correct channel for Bilsdale. The
only signals visible when I scan the output of the Emley aerial are Emley
and Bilsdale. The aerial is screened from most directions. It's in the
back yard, not on the roof.
Bill


Good great recommendation for Humax then!

Incidentally we have a half wave FM dipole (recommended by YOU) on the
aerial mast on top of our flats, probably 15m up with a clear view over the
Cheshire plain, connected to a Sony STRD-800. Gets more channels than there
are memories in the box (30) with the main limitation to DX being FM
capture.

Similarly despite being 50km from Winter Hill and the aerial signal going
through a six way distribution amp, the VCR and then a four way passive
split and lots of wire etc., the LG TV's all tune up easily.


  #16  
Old November 21st 13, 08:55 PM posted to uk.tech.digital-tv
tony sayer
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Posts: 4,988
Default Just a reminder about the sensitivity of modern DTT boxes


Agree with that in general.,.

It does seem that reception on DTV these days is better, least I can
receive DTV signals usually ones out in the office on a simple indoor
aerial whereas I could not do that before on analogue...


That is to do with reflections and image rejection. On analogue if you
lived near flats or a cliff you would get ghosting.



Nope .. this was simple lack of signal horsepower!.. Not strong enough
to raise reflected signals...

--
Tony Sayer



 




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