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Dab+ Repeater In Melbourne Cbd


alanh

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All,

The ACMA has approved test licences for 3 DAB+ repeaters on the top of 101 Collins St Melbourne. The power is 0.1 kW. The licences expire on 31st July 2010.

AlanH

good stuff, good to see them do something re reception, just whats needed in my opinion, given the very hairy reception around cbd. pity I dont have a portable dab+ receiver anymore otherwise would be able to confirm if actually helping any ! not much of a trial if license expires end july 2010 ! oh well can just hope it improves the situation !

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They may just be back-up transmitters in case of total failure to the Mt Dandenong TX (eg: not repeaters).

There's a couple of FM TX back-up's too.

It would be good if they are in fact repeaters.

Edited by mtv
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For the doubters, it is hardly a back up for Mt Dandenong at 0.1 kW each when the Mt Dandenong transmitters are 50 kW each!

These repeaters have been in the planning from before the start of official broadcasting because the effect of city buildings was known as a problem then.

CRA owns the company which has the licence for all commercial DAB+ transmitters.

These are repeaters not translators. I is likely to be a 0.1 kW digital TV transmitter tuned to TV channel 9A with its modulator removed. The signal input is a DTV receiver tuned to channel 9A with the un demodulated signal fed into the transmitter.

AlanH

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Brisbane needs translators badly. It's fantastic that Melbourne has been granted these tests, but based on my experience (and a number of other frequent posters here who have spent considerable time in both Brisbane and Melbourne metro with their DAB Plus portables) Melbourne is receiving vastly superior reception for a number of reasons.

Are there going to be translator tests licensed for Brisbane or Sydney?

Edited by Rock in stereo
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Brisbane needs translators badly. It's fantastic that Melbourne has been granted these tests, but based on my experience (and a number of other frequent posters here who have spent considerable time in both Brisbane and Melbourne metro with their DAB Plus portables) Melbourne is receiving vastly superior reception for a number of reasons.

Are there going to be translator tests licensed for Brisbane or Sydney?

Yeah sydney needs some. I think where they repeat digital TV as well as they should put a translator (or repeaters) where they have one for WS FM (99.1 FM and 88.3FM) in western sydney.

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Rock in Stereo,

The Brisbane situation is quite different to Melbourne.

The Brisbane coverage area is purposely limited to the Brisbane Metropolitan area. The reason for this is that as soon as analog TV switch off occurs DAB+ transmitters will be licenced for Gold Coast and Sunshine coast.

The Melbourne tests are probably a proof of concept. It is important to optimise the timing and radiated power levels in an area with lots of reflections and some signal from the main transmitter.

There is plenty of justification for repeaters at Kings Cross, North Head, Bouddi (South pointing only) and possibly Woronora.

If you haven't seen DAB+ transmissions are going to start in Canberra (low power) and Townsville.

AlanH

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Rock in Stereo,

The Brisbane situation is quite different to Melbourne.

The Brisbane coverage area is purposely limited to the Brisbane Metropolitan area. The reason for this is that as soon as analog TV switch off occurs DAB+ transmitters will be licenced for Gold Coast and Sunshine coast.

The Melbourne tests are probably a proof of concept. It is important to optimise the timing and radiated power levels in an area with lots of reflections and some signal from the main transmitter.

There is plenty of justification for repeaters at Kings Cross, North Head, Bouddi (South pointing only) and possibly Woronora.

If you haven't seen DAB+ transmissions are going to start in Canberra (low power) and Townsville.

AlanH

I wonder why there has never been any consideration for repeaters in western sydney for both digital TV and radio, yet it was ok to set up a translator for WS fm. Not sure why.

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I is likely to be a 0.1 kW digital TV transmitter tuned to TV channel 9A with its modulator removed. The signal input is a DTV receiver tuned to channel 9A with the un demodulated signal fed into the transmitter.

Umm...right...

You reckon? :huh:

A DTV receiver...

I have heard it all now.

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Chaosmaster,

You don't get it.

DAB+ channel 9A = 202.928 MHz

DAB+ channel 9B = 204.64 MHz

DAB+ channel 9C = 206.352 MHz

The Receiver is tuned to 205 MHz. Its oscillator is operating at 244 MHz. When these signals are mixed together you filter out the lower sideband.

DAB+ channel 9A = 41.072 MHz

DAB+ channel 9B = 39.360 MHz

DAB+ channel 9C = 37.648 MHz

These signals are present on a single cable. The receiver contains a 36 - 42 MHz filter to remove TV channels 9 and 10.

The transmitter upconverter uses the same 244 MHz and mixes with the above input you use the lower sideband and get;

DAB+ channel 9A = 202.928 MHz

DAB+ channel 9B = 204.64 MHz

DAB+ channel 9C = 206.352 MHz

These signals are amplified and fed to the antenna.

There is no demodulation decompression, recompression and modulation. which happens in a normal DVB-T receiver and DVB-T transmitter.

It is much cheaper to do it this way by connecting 2 pairs of wires between the modified DVB-T receiver and the IF input of a DVB-T transmitter. The other option is to use 3 DAB+ radios and 3 DAB+ transmitters. The sound will be worse particularly if you decompress the audio and then recompress it.

AlanH

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Chaosmaster,

You don't get it.

<Rant>

AlanH

What I do get, AlanH, is that you are (as usual) making some very big assumptions here. Prove that this is the method they are using. Yes, prove it, Alan. Something you keep asking everyone else to do when they dare :o to challenge your infallible posts. In any case, the explanation you gave for the retransmission process has nothing to do with DVB-T anyway. It's generic RF/IF translation and filtering stuff. Without a doubt specialist hardware would exist for this purpose for DAB+, so why the heck would you use DVB-T* hardware to do it???

Also, it never occurred to you that perhaps this site is fed by fibre or some other means?

(And I am really not sure why you brought up recompressing the audio - no one has suggested this, and it would indeed be a very stupid idea, as you seem to have acknowleged yourself.)

As I just said - prove it, rather than assume and pass it off as fact.

*This also flies in the face of your earlier statements in other threads about the importance of frequency selectivity in filters, amplifiers, and the like, as a system based on DVB-T hardware is clearly not going to have a frequency response that is ideally matched to DAB+ channel characteristics, nor will it have the best possible noise and gain performance, being a broadband 'whole-channel' system as opposed to a narrowband 'per-multiplex' one.

Edited by ChaosMaster
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Chaosmaster,

The problem is not being able to feed the audio to low powered DAB+ transmitters. The problem is to ensure that the frequency and phase of the signals is identical along with the delay of the data to match between the time from the studio to the transmitter and back to a receiver near 101 Collins St.

This is solution was told to me by one of the engineers in charge of DAB+ rollout. It is obvious you know little of the theory of modulation and the availablility of transmitter equipment. This is real engineering not connecting black boxes together.

Its a sad day when we have such little technical expertise in this country that they cannot connect 4 wires in the right place in a receiver.

You should be reminded of the fact that through the efforts of the CRA Australia is the first place to adopt and implement DAB+ worldwide. So there is a lot of expertise here.

The IF signal is removed after the filtering in the receiver as I stated. Signal to noise ratio is not a problem because of the line of sight reception from the top of 101 Collins St and Mt Dandenong.

The IF output to IF input to a transmitter is commonly used in translators. There is much less reduction of signal quality by needlessly demodulating and remodulating signals.

Considering that DAB+ uses COFDM modulation, the signal is composed many carriers like DTV and we are not trying to listen to individual DAB+ signals this system is quite acceptable.

The only hassle is that until analog TV is switched off, channel 9A is only 6 MHz wide instead of 7 MHz. This is one reason why there is only 3 DAB+ transmitters in Melbourne instead of the possible 4 when channel 10 analog is switched off.

Alanh

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Purely from the aspect of this particular scenario, no specialst DAB+ skill is needed as at the layer being dealt with (modulation) DAB and DAB+ are essentially the same.

My two cents worth is that either a direct RF down convert (or a system using an IF) or a more complex demod / remod system could work.

The down (or up) convert would be the easiest to implement assuming delays across the new small network fell within the guard intervals. For multiple transmitters on the same frequency using this principle the mixer frequency at each transmitter would need to be ridgedly controlled. A significant disadvantage to such a system is inherited errors. Errors in reception at the site would remain present in the signal re-transmitted on the alternate frequency. If conditions induce further errors in reception to this signal the combined error rate (from the initial RF and the re-transmitted RF) may push the transmission far enough to produce errors in the final receiver post correction, and nobody wants that. I believe that there are some RF>RF translators in use for digital television in Australia right now.

The second option needs more examination.

alanh has said that a 'DTV' - presumably DVB-t is meant - receiver is used. How does a DVB-t receiver fundamentally vary from an analogue receiver. The section we are concerned with is the RF components and demodulator. Without the demodulator there is no appreciable difference at this point between an 'analogue' receiver and a 'DVB' receiver and given that alanh has stated the use of a 'DTV' receiver it has to be assumed that there is indeed a demodulator involved for option 2. The demodulator's job is to recover the transport stream from the RF and correct the transport stream as much as possible and output it. It may output via a parrell port, but more likely it'll be serial. This recovered 'clean' transport stream is then distributed to the transmitters in the smaller network with appropriate timing and synchronisation. This system has the advantage that errors in the original transmission may be 100% corrected and not passed onto the re-transmission at all giving a more robust transmission.

Unfortunately with so many things alanh says he quite often gets the fundamentals mixed up or turned around in some fashion; or provides an amazingly unclear and confusing explanation of what he is attempting to say. It may not be wise to take alanh's statements at face value.

Perhaps where alanh refers to a 'DTV receiver' he doesn't really mean a 'DTV receiver' rather a bit of RF kit to downconvert the inbound transmission to an IF to be fed into a transmitter (instead of a DVB-t demodulator) as is done in many places in the analogue RF world. Perhaps he means an integrated RF front end / demodulator with the IF being tapped. I doubt anyone with an engineering background involved in the trial is going to speak up to reveal what is really being done so we may well never know.

As for it being 'real engineering', without attempting to belittle the skill and/or knowledge of the engineers involved, there is off the shelf 'black box' components for just this sort of application alanh. I doubt that anyone has had to reach for protel (or the likes) and a soldering iron.

Its a sad day when we have such little technical expertise in this country that they cannot connect 4 wires in the right place in a receiver.

Just as a question: What does this refer to? I can't see this sort of thing mentioned elsewhere in the thread. It seems to be a completely un-related comment.

Edited by DrP
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DrP,

An analog receiver could be used except that in professional receivers they are a dying breed. Why not use a digital one with a more stable oscillator to keep the transmitted frequency within tolerance.

Yes, there are IF connected TV repeaters and this is the same process. You do not want to alter any characteristics of the received signal because it will not be retransmitted as identical. When there is a DAB+ radio within range of the Mt Dandenong and Collins St transmitters the signal must be identical otherwise reception will stop.

You have not read my post very well as I was praising the local technical talent for getting the whole DAB+ system off and running and critisising the slur produced by the poster. The poster is suggesting that the only way to make a repeater is to DAB+ receive the signal to audio and data, then use a standard DAB+ transmitter to retransmit the signal. This will not work in repeater situations because identical signals are not produced. Have you ever thought that you could have my comments back to front??

AlanH

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Oh dear.....

Let me see if I have this right, three DAB+ channels that due to their occupying less than a single 7 MHz DVB-T channel will be received by a DVB-T receiver and the IF taken from this and feed a DVB-T transmitter with the modulator removed such that the up converter's IF input is directly fed and this output will be identical the the received signal and when transmitted will be recoverable.

Is this what is being claimed?

How are the intermods of 9c and 9b appearing in 9a handled?

How are the intermods of 9a and 9b appearing in 9c handled?

How is the isolation between receive and transmit antennas achieved in a location full of reflection sources?

"The problem is to ensure that the frequency and phase of the signals is identical along with the delay of the data to match between the time from the studio to the transmitter and back to a receiver near 101 Collins St." Absolute wank.

"This is solution was told to me by one of the engineers in charge of DAB+ rollout." He may have seen the Silicon Chip articles and is contributing to its future errata in advance.

"There is no demodulation decompression, recompression and modulation. which happens in a normal DVB-T receiver and DVB-T transmitter." The right way to run a low power DVB-T transmitter off a parent service is to receive COFDM demodulate to ASI and remodulate to COFDM, all capital city commercial translators are done this way. For DAB+ similarly COFDM/ETI/COFDM, ETI delivered to the site for COFDM modulation on 9A/B/C is the right way to go, anything else is folly.

James

Edited by James T Kirk
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...critisising the slur produced by the poster. The poster is suggesting that the only way to make a repeater is to DAB+ receive the signal to audio and data, then use a standard DAB+ transmitter to retransmit the signal. This will not work in repeater situations because identical signals are not produced. Have you ever thought that you could have my comments back to front??

It could not be clearer that you are here only to cause trouble. What did I say, you ask? I said that it is highly likely that either dedicated DAB+ RF repeater hardware is being employed, or that the signal is received by fibre from a central source (which would then be modulated identically to the signal off Mt. Dandenong using the same kinds of techniques by which this is done for DVB-T). It is quite obvious that you have not properly read TR 101 190 'Implementation guidelines for DVB terrestrial services; Transmission aspects'. Section 7.1.2 of this document, 'Decentralised generation of the COFDM signal' in relation to SFNs covers exactly this scenario, so I am not sure why you are saying it can't be done. The document describes a number of methods by which all the signals in the network can be precisely timed to ensure that problematic interference does not occur. As previously mentioned, this could easily be extended to DAB+ SFNs if so desired.

At NO POINT did I say that the signal from Mt. Dandenong is demodulated and remodulated at the repeater. You are, as usual, making things up and attempting to start a flame war. You seem to make a habit of treating like idiots and/or insulting other contributors to this forum who disagree with you, without first checking your own facts. You are nothing more than a troll, IMO.

James T Kirk above also seems to agree with me that your explanation of using television repeater hardware for DAB+ is quite absurd.

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The poster is suggesting that the only way to make a repeater is to DAB+ receive the signal to audio and data, then use a standard DAB+ transmitter to retransmit the signal. This will not work in repeater situations because identical signals are not produced. Have you ever thought that you could have my comments back to front??

Reviewing the poster's posts reveals no such claims or statements. Perhaps it is you that has things 'back to front' as usual.

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James Kirk,

I was told this about the Melbourne site prior to the articles about Digital radio. The only errors occured when the publisher published the wrong diagram. I picked it up as soon as I saw the magazine. There was no errata on all the other articles. So stop making assumptions. You were not there!

Intemod distortion is kept low by ensuring that the signal levels are correct and remember the ERP is only 100 W!

Isolation will be a problem if there is insufficient physical spacing between very directional receiving antenna. Such a low powered output will mean that isolation will be easily achieved.

If the signals from a main and repeater are not identical then errors are excessive and reception stops. This is why an SFN for TV is designed the same way. They use GPS as a frequency reference for all transmitters on the same channel. The delay between transmitters is adjusted to move the mush zone away from populated areas.

You cannot make the last statement because this is the first SFN for DAB+ in Australia possibly the world. This would be the reason for such low power because it is a trial.

How can you feed all 3 individual DAB+ signals into a single transmitter which contains one modulator? You could demodulate DAB+ back to an ASI signal using 3 receivers. This will result in 3 baseband signals. These will then need 3 DAB+ transmitters.

Chaosmaster,

You are going on about highly likely ie you don't really know what is actually being used! This is an experiment!

AlanH

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You are going on about highly likely ie you don't really know what is actually being used!

Yes, alanh, but I, unlike you, am not pretending that I do in fact know exactly what is being done. James T Kirk, whom I believe knows quite a lot about these issues, also rebutted your ridiculous claim.

This is an experiment!

Your point being...?

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You cannot make the last statement because this is the first SFN for DAB+ in Australia possibly the world. This would be the reason for such low power because it is a trial.

Well then, bringing up your own words (because I just love to throw your 'information' back at you):

SFNs for DAB+ do not work. There is no way they can work. Its simply not possible.

On what basis do I form this opinion? I use the precise same criteria you do. It is not currently done therefore it can not be done. Supporting examples of your posts can be provided to demonstrate that you have assumed this position in the past.

Thankyou. Come again. ^_^

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DrP,

An analog receiver could be used except that in professional receivers they are a dying breed. Why not use a digital one with a more stable oscillator to keep the transmitted frequency within tolerance.

A receiver with digital components (ie, local oscillator synthesis) is not what most people will think of when you referred to a 'DTV receiver'. What you are in reality referring to, based upon your information quoted above, is still very much in the 'analogue' domain.

The use of a varicap with digitally controlled voltages does not maketh an analogue TV into a digital one.

Edited by DrP
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Well then, bringing up your own words (because I just love to throw your 'information' back at you):

SFNs for DAB+ do not work. There is no way they can work. Its simply not possible.

:lol:

Yes, I do rather vividly remember alanh's patent denial of the possibility of ATSC SFNs despite all the field tests which suggested otherwise. Typical.

What is it you were saying about er...'real engineering', alanh...

Edited by ChaosMaster
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Chaosmaster,

I did not say that DAB+ SFN's do not work. It is obvious that this is what is being trialled in Melbourne. Check the frequencies used in Melbourne City and Mt Dandenong. They are identical.

I was disputing the method of doing it with a single transmitter for 3 DAB+ channels.

As for ASTC SFNs

Contrast Multipath vs Symbol Period. (Written in 2004) It was the short symbol length and guard band which will restrict the overlapping radius is why I discounted it.

You will note that the UK uses DVB-T with 2 k carriers and does not have SFNs because they are unsatisfactory. Here we use DVB-T 8 k carrier and we have SFNs.

You will note the huge number of complaints about SFNs in the NSW Central Coast Viewers' forum. and we use the 8 k method as compared to 8 level VSB. So you would have to be desperate to use SFN ASTC. So which real US broadcasters are using it?

James,

""The problem is to ensure that the frequency and phase of the signals is identical along with the delay of the data to match between the time from the studio to the transmitter and back to a receiver near 101 Collins St." Absolute wank." See Multiple Coherent Transmitters slide 5 and Slide 10

DrP,

They would not try it if they thought it was impossible. It is just as possible as the DVB-T ones.

AlanH

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