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49 posts

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Topic # 54055 15-Dec-2009 23:29
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I am looking for some guidance on what is an acceptable signal strength at the input of a integrated digital television (iDTV)/DTT receiver, Freeview HD receiver or  Freeview HD digital television recorder (DTR)/personal video recorder (PVR).  I presume the two most important measurements of a DTT signal are strength and quality, ie, bit error rate (BER).

In an analog system, such as the free to air VHF and UHF signals that we have all used in the past, the two most important radio frequency measurements have been signal strength (dbµV) and carrier to noise ratio (C/N).  A signal strength of 70dbµV and C/N in excess of 43 dB would be considered quite acceptable.

What are the comparable signal strength and bit error rate reqirements/standards for New Zealand's DTT/Freeview signals?  I would appreciate it if someone could point me to a reference or source for this information.

Once I know what I need I come to the equipment limitations I face.  I have a TV signal strength meter and an HP spectrum analyzer both capable of making VHF and UHF signal strength measurements (dbµV).  They are both reasonably accurate and in agreement in making measurements on analog TV signals.  What should I expect when I use them to measure a DTT signal?

I will be making the measurements on the MATV system that serves the apartment building where I live.  I do not have a Freeview HD receiver or equipment capable of measuring BER on a digital signal.  Your help in guiding me in how to use the equipment I have is very much appreciated.

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49 posts

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  Reply # 284042 19-Dec-2009 16:24
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Shameless BUMP!

As an old cable TV engineer, back in the 1980's, I am somewhat compulsive in wanting to quantify the quality of the Freeview HD signal available on the MATV system in my apartment building.  None of my neighbours have Freeviewq HD so I would like to know it will work before I go out and buy a Freeview HD PVR.

Can anyone provide some guidance on what the signal strength should be on the DTT channels and how to measure it?  I am in the Auckland CBD and would probably use the Skytower, (23, 32 & 40) channels/multiplexes or Waiatarua (29, 33 & 45).  Your help would be very much appreciated.  Thanks!

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  Reply # 284045 19-Dec-2009 16:39
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Hi, the AS/NZ standard states that for DVB-T transmissions you should have 50-74dBuV provided to a faceplate, as opposed to 60-80dBuV for analog for Multi dwelling units. For single dwellings the levels can be opened up a few dB, ie 45-80dBuV for DVB-T.


Cheers
Cyril

 
 
 
 


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  Reply # 284124 20-Dec-2009 02:58
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mail2mm: Shameless BUMP!

Can anyone provide some guidance on what the signal strength should be on the DTT channels and how to measure it?  I am in the Auckland CBD and would probably use the Skytower, (23, 32 & 40) channels/multiplexes or Waiatarua (29, 33 & 45).  Your help would be very much appreciated.  Thanks!


Hi mail2mm,

In Hamilton we get excited if we are getting 50 to 55 db from the digital channels at the aerial and 40 to45 at the faceplate! - I presume that you can expect a lot more than that in Auckland as your transmitters are a lot closer, and Waiatarua is twice as powerful; (we get it from Te Aroha 50Kms away).

The threashold (point where pictures start pixilating) seems to vary between 30 to 35db for TVs with the built in DTT receiver and 35 to 40 for stand-alone DTT receivers.

You will be able to measure the signals on your signal strength meter just the same as measuring the analogue channels.

Cheers Wild Bill



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Reply # 284235 20-Dec-2009 20:00
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My thanks to Cyril and Wild Bill for your helpful responses.  I will post the result of my measurements of signal strength and C/N when I do them.

In the meantime I did some Google searching for:


Australian/New Zealand Standard AS/NZS 1367:2007
 
Coaxial cable and optical fibre systems or the RF distribution of analog and digital television and sound signals in single and multiple dwelling installations

Yikes! At $202.45 + GST for a downloaded version at www.standards.co.nz I will have to do without the "source" document as much as I would like to have it.  I did find a very interesting and useful UK publication.  While not wholly applicable to NZ it provides useful tutourial and advanced information to a digital TV novice like me.  In addition to signal level, C/N and BER I now find that operating margin is an important measurement of reliability in a digital TV system.  From the UK publication, "Operating margin can be measured quite simply by temporarily inserting a variable attenuator into the aerial feed and determining the maximum amount of attenuation that can be introduced before decoding fails."  If I find Freeview HD is on our SMATV system, then buy a suitable receiver (Magic TV?) I will see if I can access the actual aerial feed for the headend to make this operating margin measurrement. 

Is operating margin measurement something professional MATV installers do on a system carrying Freeview HD?  If so what are typical and/or acceptable results?

The pdf document is:

Installing Digital Television - MATV and IRS, Digital TV Group, R-book 5, July 2005. 

I found it at:

www.dtg.org.uk/industry/publications.html

Thanks again for your assistance.  I apologise for the long post.  Sometimes it helps me to just write down my thoughts.

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