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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.

Problems today with muxes 7 and 8



 
 
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  #61  
Old February 20th 18, 09:11 PM posted to uk.tech.digital-tv
Andy Burns[_12_]
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Posts: 573
Default Problems today with muxes 7 and 8

The Other John wrote:

I've done a scan using RTLPan


I didn't find that one.

but it doesn't give a nice clean display like yours, see:
https://www.dropbox.com/s/b7w9z8kyza...22018.bmp?dl=0


RTLSDR Scanner has a "smoothed" mode that looks sort of like that, it
looses all the detail, compare

http://andyburns.uk/misc/Waltham_CD.png
http://andyburns.uk/misc/Waltham_CD_smoothed.png

Give it a try

https://eartoearoak.com/software/rtlsdr-scanner

My muxes on the Reigate TX are currently at both ends of the band and
although I'm using the old analogue group C/D aerial, it doesn't matter
much because I can see the TX mast from my house.


I scanned the group A "end" of Waltham, as well as the group C/D "end"

http://andyburns.uk/misc/Waltham_A.png

the only remarkable thing about it is that hiding within the noise at
514MHz is the Nottingham local mux, which my TV is perfectly happy to
receive, fair enough it uses QPSK so is more robust.
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  #62  
Old February 20th 18, 10:12 PM posted to uk.tech.digital-tv
Andy Burns[_12_]
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Posts: 573
Default Problems today with muxes 7 and 8

Bill Wright wrote:

I would have thought that any AGC effect with a longish time constant
would cause the slope to be always downwards starting at the side
where the scan starts. The variations across your muxes are random.

I did a full band IV/V scan, it will be interesting to compare with in
2020 after the 700MHz clearance is over. From my location south of
Leicester, I have a DML26 pointing at Waltham, which happens to also be
a direct line to Belmont in the distance. Sutton Coldfield is sort of
behind the aerial at about a 30° angle, but closer.

http://andyburns.uk/misc/CH21-CH68.png

The shape of the tops of the muxes between my group A and C/D scans,
compared to the whole 21-69 scan, do seem similar.

Incidentally your scan seems to have been made with a very narrow
bandwidth, hence the good definition.


The bandwidth of each individual capture can't be more than about
2.5MHz, whether it does the FFT transform on each of those individually
and stitches the spectrum together, or whether it somehow "sums" all the
captures, and then FFT's that as a big capture to a spectrum, I don't know.

I got the feeling it was struggling to give as good resolution for the
whole band scan, I tried increasing the FFT size from 1024 to 2048, but
it kept running out of memory (even on a 16GB machine).

You know how some pictures really *are* worth 1,000 words and you wish
you'd seen them much earlier?

https://upload.wikimedia.org/wikipedia/commons/6/61/FFT-Time-Frequency-View.png
  #63  
Old February 20th 18, 11:14 PM posted to uk.tech.digital-tv
The Other John[_2_]
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Posts: 70
Default Problems today with muxes 7 and 8

On Tue, 20 Feb 2018 21:11:40 +0000, Andy Burns wrote:

Give it a try

https://eartoearoak.com/software/rtlsdr-scanner


Thanks for the link Andy, I'll give it a go tomorrow.

--
TOJ.
 




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