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C31 Digital Reception Problems

C31 44 MGV32 community TV

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#1 breakfastofchampions

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Posted 19 January 2012 - 05:46 PM

Over the past couple of weeks I have encountered problems receiving C31 Digital. I live in Ormond in an apartment block and currently use a Tandy/Dick Smith indoor VHF/UHF antenna with booster. Until recently I have been receiving all digital channels in Melbourne no problems at all. Then I noticed that my C31 picture is either heavily pixelated, static or has no signal. All other channels are not affected and can still be received clearly. Does anyone else have this problem?

#2 mtv

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Posted 19 January 2012 - 07:30 PM

Where are you receiving your TV signals from... Como or Mt Dandenong? eg: what frequency have you tuned C31 digital on? Como is 795.500MHz. Mt Dandenong is 557.625MHz

C31 digital is very low power compared to all other networks.

#3 alanh

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Posted 19 January 2012 - 07:35 PM

BreakfastofChampion

MGV has a pair of digital transmitters
Mt Dandenong Transmission channel 32 15 kW compared to SBS on transmission channel 29 which is 200 kW power.

Como Centre Level 22 N-E cnr 620 Chapel St SOUTH YARRA
has a MGV transmitter on transmission channel 66 with a power of 0.006 kW power. The antenna needs to be on its side to receive it.

Once scanned in the installation menu either transmission is selected by selecting channel 44.

1st March the analog channel 31, 64 transmitters will be switched off.

In 2014 the existing channel 32, 66 will be switched off and the programs will be transmitted either on transmission channel 10 or with SBS on transmission channel 7.

Do you have a Master Antenna TV system with an antenna connection on the wall. If so then it will work in 2014.

In the mean time read the first post in http://www.dtvforum....showtopic=11399 particularly the link to indoor antennas and Mt Dandenong is in category H34 and South Yarra on V5.

AlanH

#4 breakfastofchampions

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Posted 19 January 2012 - 08:13 PM

In answer to your questions:
(1) I get my TV reception from Mt Dandenong
(2) I do have a master antenna system but it is very old (ribbon), the antenna is hidden in the roof and only receives 2, 7, 9 and 10 analogue.

Why can't they have the same power as other stations? They will need to if they are going to cover all of Melbourne.
As I said before I used to get C31 in digital but not anymore. It seems that C31 has lowered the power on their digital transmitter.
An outside antenna is not an option as it costs a lot of money for a 10-unit block, reception in this part of Melbourne requires fringe-area antennas, and it involves a lot of body corporate red tape.
Also, why doesn't Foxtel carry C31

#5 breakfastofchampions

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Posted 19 January 2012 - 08:14 PM

Also, why doesn't Foxtel carry C31?

Optus Vision used to carry it years ago.

#6 alanh

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Posted 20 January 2012 - 01:06 AM

Breakfast of champions,
The power of the channel 32 transmitter has always been a lot less than the equivalent which is SBS. The point is that not all of Melbourne/Geelong can receive this signal. The only community TV transmitter which is the same power as SBS is West TV in Perth. The reason why they have less power is the cost of purchase and running transmitter increases with power.

All analog TV transmitters in Melbourne will be switched off at the end of next year.

You do not say how many apartments are in your building and whether it has a single owner or if it's strata title.

AlanH

#7 breakfastofchampions

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Posted 20 January 2012 - 09:47 AM

Breakfast of champions,
The power of the channel 32 transmitter has always been a lot less than the equivalent which is SBS. The point is that not all of Melbourne/Geelong can receive this signal. The only community TV transmitter which is the same power as SBS is West TV in Perth. The reason why they have less power is the cost of purchase and running transmitter increases with power.

All analog TV transmitters in Melbourne will be switched off at the end of next year.

You do not say how many apartments are in your building and whether it has a single owner or if it's strata title.

AlanH

10 apartments, each have a separate owner.

#8 mtv

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Posted 20 January 2012 - 10:18 AM

If the MATV system is poor, it requires upgrading.

Having the antenna 'hidden in the roof' will make the problem worse.

Given the age of the cabling (coax cable was introduced when colour TV commenced in Australia in 1975) the antenna may also be very old and not suitable for the digital channels and possibly only designed for VHF.

It would be a reasonable assumption that other residents would also be experiencing poor digital reception from the MATV system and it would be beneficial to all to have the antenna and distribution system ugrded to digital standard.

The cost should be divided among the 10 owners.

Other options you could try is moving your indoor antenna around the room. You may need an RG6 Quadshield extension cable to move it away from the TV.

You could also try tuning the Como frequencies, but keep in mind C31 from Como is very low power.

Edited by mtv, 20 January 2012 - 03:24 PM.


#9 CWulf

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Posted 20 January 2012 - 10:19 AM

Hi

As usual Alan has taken a little bit of information and knowledge and run with it in completely the wrong direction!

Yes, the CTV services are operating at a lower ERP than the SBS but they are also operating with a much more robust modulation mode which effectively provides the same coverage! Possibly there are some cost considerations but it is really that the government has only allowed the CTV licensees to provide one program stream which only requires a limited bitrate.

I'm not an installer and could summise that your change in reception could be due to changes in trees, foliage, weather, your antenna system, local interference but the only way to really know is to get an installer out to check.

Also note that Alan is guessing that the CTV services will continue post analog restack and shift to VHF channels or carriage with the SBS. This may happen but is certainly not guaranteed. Alan's often been criticised for posting from a position of certainty when in fact he is an armchair expert making (possibly) educated guesses!

I suspect Alan will come back wanting to debate with me but I'm not trying to enter a debate, just give some balance to his "advice".

#10 pgdownload

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Posted 20 January 2012 - 10:45 AM

What happened to one of the big four including C31 in their mux? is this definitely no longer an option?

Regards

Peter Gillespie

#11 alanh

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Posted 20 January 2012 - 01:05 PM

CWulf,
More error correction is irrelevant if the signal level is so low that the receiver cannot detect it.

This is also true of West TV yet the power is the same as SBS.

AlanH

#12 CWulf

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Posted 20 January 2012 - 03:27 PM

Alan

QPSK versus 64 QAM does make a difference!

Perth CTV is equivalent ERP as it is transmitting 64 QAM. Other CTV services are lower ERP as they are transmitting in QPSK!

#13 mtv

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Posted 20 January 2012 - 03:29 PM

Both Sydney and Melbourne generally have good reception of the digital community channels.

I'm often amazed by the performance in regard to BER/MER of those channels, which in some cases is far superior to all other networks, regardless of transmission power.

CWulf is correct, that there are many variables which can cause changes in received signal performance.

Without accurate signal measurements, it's impossible to know exactly what your signals are doing.

The key to reliable digital reception is the right antenna, mounted in the right location.

#14 Malich

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Posted 20 January 2012 - 04:18 PM

I'm often amazed by the performance in regard to BER/MER of those channels, which in some cases is far superior to all other networks, regardless of transmission power.


You're probably aware of it, but compare the modulation parameters of the community channels to the national broadcasters sometime. Briz31, last I looked, was using QPSK (and, IIRC, a guard interval of 1/8), which is a helluvalot more robust than QAM64 & 1/16.

(edit: And I see that's been covered [and argued about, as per usual :no:]. Serves me right for only looking at the last post in the thread!)

Edited by Malich, 20 January 2012 - 04:25 PM.


#15 breakfastofchampions

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Posted 15 February 2012 - 11:44 AM

I can now receive C31 on digital 44 again :)

#16 alanh

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Posted 15 February 2012 - 08:27 PM

CWULF
Firstly after the digital restack the only RF channels to be used in state capital cities are;
Channel 6 carrying the 7 network
Channel 7 carrying SBS
Channel 8 carrying Nine network
Channel 9 DAB+ radio
Channel 9A DAB+ radio (not used in capital cities but surrounding areas)
Channel 10 Unallocated
Channel 11 carrying the TEN network
Channel 12 carrying the ABC.
The ACMA is going to change SBS to 64 QAM when they move to channel 7. Since the only community TV stations are in mainland state capital cities it is entirely possible that they may be added to the capital city SBS feeds to use their spare capacity. This will leave channel 10 and its UHF equivalents free for a nationwide network.
Other restack groups are
Group B channels 28 - 33 inclusive
Group C channels 34 - 39
Group D channels 40 - 45
Group E channels 46 - 51
On any individual site the same polarisation is used for all 6 transmitters. Sites may be vertical or horizontal polarisation.

The commercial DTV rollout is all using the above channel groups. Some ABC/SBS channels may need to change channels.

Search digital restack on the ACMA site if you don't believe it.

As for the relationship between power and QPSK/64 QAM. The first thing which a receiver must do is to detect and measure the pilot frequencies in the signal. If the power is insufficient then it is irrelevant what type of modulation is used. If the pilot cannot be used to lock the decoding clock the modulation type is irrelevant. Once this lock occurs then QPSK only has 4 phases of full modulated power, whereas 4 levels of power in 4 phases gives 64 states.

So as I have said once the receiver is locked on a signal then there is much better noise immunity using the low capacity QPSK. However if the signal field strength is too weak no reception is possible.

The field strength is 11 dB lower than SBS for MGV32 and for South Yarra MVG66 it is also 11 dB lower than the other transmitters.
AlanH

Edited by alanh, 15 February 2012 - 08:49 PM.