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Discussion Starter #1
Hi,


We have an analog head-end where we are transmitting free analog channels. Now, we want to transmit SD and HD channels but without using any set-top-boxes. Since, it is intended to be free for all.


I want to know what are the equipment needed for this task. How much band width one HD channel consumes?


Thanks in advance.
 

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Need a little more info. What source is providing you analog channels now? Do you use STB's now?


What tv's do the recipients have? HDTV? SDTV?


Is this for a building, school, business, etc? How many recipients?


Basically, the easiest and simplest way you are going to transmit HD channels for free is to receive channels over the air with an antenna ( assuming you are close to the towers), and assuming all of your recipients have HDTV's with tuners already built-in, transmit them from your distribution head end with distribution amplifier and splitters, depending on how many tv's you are serving. No STB's needed.
 

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You need a device called a QAM modulator. As well as a source to feed into it. Antenna is probably the way to go.


As for bandwidth, 2 ~19 Mbps HD channels can fit in 1 6 MHz QAM channel.
 

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First, you'll need to describe what you are already doing....


If you are only carrying channels that are OTA-style channelization (the frequencies are the exact same as over-the-air, and the TV's all work on "antenna" mode), you can use Digital TV Channel Processors. These simply tune each station, correct the levels and filter the bandwidth, and output the signal on the same, or a different, OTA channel. You'd need one for each station. These are designed for systems that use adjacent channels, and they process the signal bandwidth tightly, so as to not interfere with the channels next to the digital.


An alternative would be something like the Johannson Profiler-series Programmable Digital Filter-Amplifier, which would process blocks of OTA channels. These may not be tight enough to allow insertion of any locally-generated "closed circuit" channels, though, unless they are a separated a bit form the OTA channel frequencies.


If you have any cable TV channelization (where the sets need to be in "Cable" mode, then you'd need to use a pair of modules for each channel....an ATSC OTA decoder (which recovers the entire Transport Stream from each station), and a QAM Modulator, that turns the transport stream in to the QAM-style modulation that the TV's look for when in Cable mode. Often, there is an RF upconverter needed for each channel, as well.


Are you running any channels of "closed circuit" cameras, satellite-fed programming, etc?
 
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Discussion Starter #5
Thank you all for the responses. I will give some describtion of our system.


We are recieving channels over the air and send to subscribers over HFC network. We are serving a small city for free and customers are not using any STBs.


Of course, not all residents have HD ready TV, so we will have a collection of analog, SD and HD. But the service is still free, so no STBs should be involved.
Quote:
for bandwidth, 2 ~19 Mbps HD channels can fit in 1 6 MHz QAM channel.
What will be the type of QAM? Can this modulated signal be decoded by the most common TVs nowadays?
Quote:
If you have any cable TV channelization (where the sets need to be in "Cable" mode, then you'd need to use a pair of modules for each channel....an ATSC OTA decoder (which recovers the entire Transport Stream from each station), and a QAM Modulator, that turns the transport stream in to the QAM-style modulation that the TV's look for when in Cable mode. Often, there is an RF upconverter needed for each channel, as well.
Yes sir, we have cable TV channelization. But correct me if I am wrong. In order to transmit HD channel, we will need:
  • ATSC OTA decoder : which is a normal HD satellite receiver.
  • QAM Modulator: to modulate the signal to be carried on 6 or 7 MHz channel.
  • RF upconverter: I need some information about this component. Is it a separate unit? what its function?


Thank you all for your contribution.
 

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Quote:
Originally Posted by cgmv123  /t/1421211/catv-head-end#post_22238273


You need a device called a QAM modulator. As well as a source to feed into it. Antenna is probably the way to go.


As for bandwidth, 2 ~19 Mbps HD channels can fit in 1 6 MHz QAM channel.

Since the signals are OTA, why bother with QAM? The TVs with digital tuners can tune the channels directly. Those that still have analog TVs will need one of those cheap digital to analog converters that also pass through the analog signals.
 

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If all you are doing is taking OTA and using coax to transport why do anything but amplify? It's already digital and modulated on a freq that a tv tuner will accept. All you need to worry about is how deep are my amp cascades and what is my end of line signal going to look like. Your subs will need same equipment that would be needed to put up their own antenna.
 

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Discussion Starter #8
Thanks for the reply Mr.domino92024 and Mr.RollTide2011.


I think both of you agreed that I should transmit the signal without any QAM modulation. Actually, we are doing this for 2 channels now, but the quality is not so good. I don't know if using QAMs can help us to get better results? For this reason I am asking about QAM and what type of QAMs are recommended by you.
 

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Quote:
Originally Posted by Yanbu  /t/1421211/catv-head-end#post_22239800


Thanks for the reply Mr.domino92024 and Mr.RollTide2011.


I think both of you agreed that I should transmit the signal without any QAM modulation. Actually, we are doing this for 2 channels now, but the quality is not so good. I don't know if using QAMs can help us to get better results? For this reason I am asking about QAM and what type of QAMs are recommended by you.

I am curious about what you really mean by "...but the quality is not so good." Please explain.
 

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Discussion Starter #10
I mean by transmitting the signals directly we are not getting the expected HD quality. For this I am asking if adding QAMs will enhance the quality or not.
 

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Quote:
Originally Posted by Yanbu  /t/1421211/catv-head-end#post_22241601


I mean by transmitting the signals directly we are not getting the expected HD quality. For this I am asking if adding QAMs will enhance the quality or not.

I am still a little "fuzzy" about what you are experiencing, but generally no.
 

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Thank you Mr.domino92024 for the reply.


You are saying that adding QAMs will not enhance the quality. But sir, I think transmitting digital signals will improve the quality.


In the current setup we are doing like this:

In the head-end: we have a reciever that receives the signal and convert it to analog RF. then, this signal is modulated to a specific frequency before going to combiner and destribution.

In the houses: users are connecting the cable directly to TVs. Even analog TVs can recieve these HD channels.

So we are transmitting analog. And I think this is the cause of the problem.


Please correct me if I am wrong.
 

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Quote:
Please correct me if I am wrong.

You have a lot of misconceptions.
Quote:
In the head-end: we have a reciever that receives the signal and convert it to analog RF. then, this signal is modulated to a specific frequency before going to combiner and destribution.

This is an analog SD signal, modulated onto CH3 or 4.
Quote:
Even analog TVs can recieve these HD channels.

they're not in HD.
 

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In a previous post, it sounded like there were 2 channels you were transmitting in digital format, but they had poor picture quality. Apparently, that was not the case.


You don't re-transmit channels in either HD or SD. You just re-transmit exactly what the TV channel is broadcasting. The customers' equipment determines whether they view it in HD or SD.
 

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Quote:
Originally Posted by SAM64  /t/1421211/catv-head-end#post_22242460


This is an analog SD signal, modulated onto CH3 or 4.

It sounds like they are a municipality (perhaps in a mountain valley or some other place where it is difficult for residents to receive OTA), and they merely have a headend at some location where they receive local channels OTA and distribute them to the community.


But in a thread in another forum, he said they have a 1GHz system with headend gear that goes up to 870MHz, and he would like to upgrade the headend to 1GHz. That's an awful lot of bandwidth for just locals.
 

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A cable TV system that is distributing analog channels on "cable STD" frequencies should "transcode" its off-air 8VSB signals to QAM just because the TV tuners will not "see" any UHF channels since there is insufficient capture range in digital TV tuners, and most digital TV tuners will not process 8VSB signals even when they have been frequency shifted to Cable STD frequencies.


As far as QAM distribution of so-called cable-TV programming is concerned, you would have to have a programming source. A substantial cable TV company would probably receive each channel via C-band, and a low budget independent local cable company would probably get its programming from Headend-in-the-Sky or whatever its present incarnation is called. What you do with that output depends on its form. If the C or Ku band receiver only has analog, component outputs, then it has to be encoded to MPEG2 and then modulated. Those two steps can be combined in many off-the-shelf QAM modulators that now sell for around $1,000 each.


But if you are using DirecTV or DISH Network and not subscribing through a Transport broker, then you would have to have their permission and cooperation to distribute cable TV programming in HD, because even if they were to activate an HD receiver in the headend, the HD receiver would not be able to select the HD channel number unless DirecTV or DISH had explicitly authorized it to do so, which they do not ordinarily do.


Who are you buying the cable-TV type programming from at present?
 

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Quote:
Originally Posted by Yanbu  /t/1421211/catv-head-end#post_22241859


Thank you Mr.domino92024 for the reply.


You are saying that adding QAMs will not enhance the quality. But sir, I think transmitting digital signals will improve the quality.

OTA is ATSC 8VSB digital to begin with. Converting to QAM modulation will gain nothing except better bandwidth management.
 

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Quote:
Originally Posted by domino92024  /t/1421211/catv-head-end#post_22243337


OTA is ATSC 8VSB digital to begin with. Converting to QAM modulation will gain nothing except better bandwidth management.
See Post # 16 for two things you would "gain" by converting the 8VSB to QAM.
 

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And.... 8VSB is an analog modulation scheme that carries ATSC (digital) information.
 

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Quote:
Originally Posted by Yanbu  /t/1421211/catv-head-end#post_22237909


Hi,

We have an analog head-end where we are transmitting free analog channels. Now, we want to transmit SD and HD channels but without using any set-top-boxes. Since, it is intended to be free for all.

I want to know what are the equipment needed for this task....
Quote:
Originally Posted by egnlsn  /t/1421211/catv-head-end#post_22242586


...But in a thread in another forum, he said they have a 1GHz system with headend gear that goes up to 870MHz, and he would like to upgrade the headend to 1GHz. That's an awful lot of bandwidth for just locals.

In order to tune any channel above 870 MHz, the customer would need a set-top box, because TVs only tune up to channel 135.
 
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