Help building a QAM Headend - AVS Forum
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Old 07-24-2014, 08:52 PM - Thread Starter
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Help building a QAM Headend

I am trying to upgrade an analog headend to a QAM headend.

Looking for help on how to best convert DTV to QAM.

Currently have DTV Receivers with composite, S-Video, and RF outputs, can upgrade to component or HDMI receivers.

Can by inexpensive QAM modulators on eBay, but not sure which ones to buy, trying to keep price point to less than $400 per channel.

Most modulators have either an IF input, ASI, or DVB input.

Which is the best to use?

Can someone explain the IF input and what type of signal this must be (these seem to be the less expensive modulators)?

I have found converters that will convert HDMI to SDI. Will SDI work for a source to these modulators either ASI or DVB?

What are your thoughts on using the Wavecom UC4040D or the Scientific Atlantic D9476 (other lost cost options)?

Any insight and help would be greatly appreciated.

Thanks,
Ken
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Old 07-24-2014, 09:39 PM
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Modulators with an IF input are just upconverters. They take an already modulated QAM RF signal at usually 70 MHz and upconvert the signal to a cable TV channel (for example, channel 58 at 429 MHz).

SDI and HD-SDI is an uncompressed interface. DVB-ASI is a compressed interface. They are not compatible with each other. To convert from SDI, HD-SDI or HDMI to DVB-ASI, you need an MPEG-2 encoder.

There are QAM modulators with built-in encoders.

http://www.zeevee.com/products/zvpro

Ron

HD MPEG-2 Test Patterns http://www.w6rz.net

Last edited by dr1394; 07-24-2014 at 09:49 PM.
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Old 07-27-2014, 06:20 AM
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What type of controller are you working with and how many channels do you want to broadcast.
There are lots of questions to answer but lets start with these.
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Old 07-27-2014, 09:31 PM - Thread Starter
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Thanks for your answers.

This is a outdoor bar on the beach with an existing SD headend (salt air eats up DTV recievers every 6 to 8 months so I built a headend roughly 22 channels and moved the receivers inside. 20 Outdoor LCD TV's last 6 to 8 months before I have to replace circuit boards).

Owner wants HD so I installed an OA antenna for local HD programming and tried to insert my existing channels and learned the hard way the difference between ATSC frequencies, Cable frequencies and analog modulators.

Installed a low pass filter on my ATSC OA antenna passes up to CH64, found out my TV's when in ATSC mode won't tune above CH64, so I am limited what available frequencies I can insert. And ATSC modulators aren't as readily available as QAM modulators. Not to mention individual channel notch filters.

So my next costly attempt was to purchase an ATSC to QAM Transcoder chasis, only to learn the one I purchased a BT QTR doesn't go low enough in the ATSC frequencies to transcode my local OA channels to QAM channels I can use.

I believe my best solution is to bite the bullit and re-install the DTV Recievers at each TV @ $150 per tv (I have roughly 30 TV's) and replace twice a year or find a headend solution before Football Season begins.

I was hoping to convert my OA channels to QAM and then modulate the 22 or so DTV channels at first in SD and then upgrade them 1 at a time to HD.

Any other thoughts would be appreciated.

THX Ken
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Old 07-28-2014, 08:20 AM
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You really need to involve a local DirecTV commercial dealer in this project.

You also need to look up the frequency channel allocation plans for broadcast TV and cable. They are the same for channels 2-13, but after that, broadcast or UHF channel 14 is roughly, but not exactly, the same frequency as cable channel 65, and the highest broadcast band channel that contemporary TV channels can tune, channel 69, is about the same frequency as cable 125.

There are different ways to integrate digital broadcast signals and digital satellite cable channels into on single coax, but all involve tradeoffs and have drawbacks. If you have LG TVs, there are a lot of ways to combine the signals with relatively low priced headend equipment because the LG TVs can often either decode broadcast TV signals when they are simply frequency shifted into cable channel slots, or some LG TVs can actually map broadcast and cable channels into the same channel guide.

If you are simply planning on taking a bunch of receivers that are activated as individual television tuners and modulating them, that is probably a violation of your terms of service agreement. DirecTV can allow that for your class of customer, but under a different contract and pricing structure.

Do you have current relations with your local DirecTV dealer, and do you know if they are able to service a small private cable headend?
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Old 07-28-2014, 10:12 AM
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So the source of your present channels is Direct TV?
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Old 07-28-2014, 09:37 PM - Thread Starter
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Originally Posted by RCbridge View Post
So the source of your present channels is Direct TV?
Yes DTV in a closed system for Bar TV's only.

Owner going to bite the bullit and purchase DTV receivers for each TV and upgrade to SWM system.

Because new receivers produce less heat and might not need excessive cooling, might be able to seal recievers to portect from salt air.
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Old 07-29-2014, 08:38 AM
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Quote:
Originally Posted by hppygo View Post
...Because new receivers produce less heat and might not need excessive cooling, might be able to seal recievers to portect from salt air.
Now that power supplies are separate units, that does make them run cooler, but if you do seal them, I'd say that you should devise and construct receiver compartments with large heat sinks that are designed to assure fairly efficient heat conduction from the receiver to the heat sink. That might entail actually removing the cases from the receivers.
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