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Author Topic: "Internal" cable broadcasting equipment  (Read 2699 times)

Chris Clark

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"Internal" cable broadcasting equipment
« on: January 07, 2015, 07:55:36 am »

I've been helping my sister, who is the technology teacher (and as a result "network admin" and designated all-around "technical person") at a small private (Catholic) school, with their network and technology infrastructure lately. Recently the subject of their TV network came up and I'm looking for some insight - if PSW isn't really the best place for this let me know but I figured I'd try where I'm already registered before going out and finding another forum to try to ask this on.

The current situation is this - They have an old Technicolor C1A2 headend that was provided by ChannelOne Networks many many years ago (she's been there 10 years and it was there before her). They are using this at this point strictly to broadcast their own programming (live morning announcements on video and a message scroller at other times). They hadn't attempted to use the ChannelOne Daily News broadcast in a while, but when we were investigating this unit for other purposes we noticed that there were no broadcasts recorded lately and C1 has no mention of the satellite feed on their website anymore, so we're presuming they've discontinued this. Additionally we've tried contacting them but can find no support for this headend anymore.

In addition, we've had to disconnect the incoming feed from the local cable company from the input to this headend as the C1 internal broadcast appears to be preset to channel 3 with no way of changing it, which interferes not only with the channel 3 feeding from the cable company, but also causes interference on every other channel. They don't care about the C1 broadcasts anymore but are looking to be able to have both the "internal" channel as well as the cable feed to the classroom TVs. We don't care if it stays on 3 or moves to something higher, outside of the range that the local company feeds to the school. Additionally HD/QAM is not a concern - all TVs are CRTs and will likely not be upgraded unless it becomes absolutely necessary, but that would probably be years down the road.

I've looked online and what I can figure would be something like a Blonder Tongue AM-60-550 (agile) or BAVM-860SAW (non-agile, not preferred but acceptable as long as cable company doesn't add to channels they send our way), and an HPC-8, although this specifically states "single channel sources" - would this cause a problem with the input from the cable company or would I need to jump to something like an OC-8D?

So I guess, TL;DR and the overall question is this:
What equipment would we need to replace the C1A2 headend for modulating a regular video input to a CTV channel (preferably frequency agile, but if not something that is set for one of the higher channels) and still combining this with the local cable company's feed (filtered so that we're not backfeeding). Budget would be in the $1000 to $1500 at most range. This doesn't need to be anything fancy, we're not running a master control here, just the morning announcements, occasionally an educational dvd, and message scroller at other times? We already have the sources (camera, DVD Player, and computer for scrolling).

Any products I've already mentioned are strictly things I've found that I think will work, there is no bias towards that company and I'm open to any suggestions you might have. Thanks in advance!
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Alex Donkle

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Re: "Internal" cable broadcasting equipment
« Reply #1 on: January 09, 2015, 05:28:59 am »

Blonder Tongue makes good gear, the other main brand to look at is Contemporary Research. I'm mostly familiar with their QAM gear so I'm not much help on analog.

The one piece of equipment I don't see is a channel elimination filter (CEQ). Most cable companies pack as many channels into the signal as possible, so there aren't any "empty" channels. A CEQ will remove 1 channel from the cable companies signal, so that when you add your own channel it won't overlap and cause interference issues. The CEQ and in-house TV channel modulator you get need to be on the same frequency for this to work. Pick whatever frequency you wish to use based on the channel you'd like to knock-out (generally whatever channel no-one watches is best).

It would also be worth looking at the frequency ratings of the CATV amplifiers and taps. Modern equipment is rated up to 1GHz for digital CATV, but analog gear may only go up to 550MHz, and older analog gear may not even go that high. Check the frequency you want to use will actually work throughout all the the TV's in the school.
« Last Edit: January 09, 2015, 05:34:41 am by Alex Donkle »
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Lee Douglas

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Re: "Internal" cable broadcasting equipment
« Reply #2 on: January 09, 2015, 04:40:59 pm »

Provided your distribution system is good, this should be an easy fix.  An SDTV frequency agile modulator can be had for pennies on the dollar as they don't work with HDTV signals.  I've got several laying around gathering dust.  This will allow you to place a modulated channel well outside of standard analog cable channels. The other thing I would put in place would be a low pass filter (or channel eliminator as Alex mentioned) on the incoming cable feed to block all the channels that you don't need above a certain frequency and clear them up for the modulated channel.  You might want to talk with a local AV integrator and see if they have any of this stuff taking up space like I do.
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Chris Clark

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Re: "Internal" cable broadcasting equipment
« Reply #3 on: January 09, 2015, 11:08:06 pm »

Thanks for the idea on the filter/channel eliminator - Something I'll look into definitely, I would have just assumed the local cable company (TWC, in case anyone was interested) had a LP filter already but I guess it definitely wouldn't hurt to make sure of that on our end.

But otherwise, with the addition of a filter, the conecpt of a modulator on whatever channel is needed and the combiner will work? Does it make a difference if the combiner claims "single channel sources" or not? (as in, the apparent difference between the HPC-8 or the OC-8D I mentioned above)

Thanks again, I (and my sister) appreciate your help!
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Alex Donkle

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Re: "Internal" cable broadcasting equipment
« Reply #4 on: January 12, 2015, 04:10:58 pm »

But otherwise, with the addition of a filter, the concept of a modulator on whatever channel is needed and the combiner will work? Does it make a difference if the combiner claims "single channel sources" or not? (as in, the apparent difference between the HPC-8 or the OC-8D I mentioned above)

Thanks again, I (and my sister) appreciate your help!

That starts to get a little more complicated. The signal levels (measured in dBmV) change throughout the CATV system due to loss in all the passive components. Typically the level at the headend is much higher than you would see at the final wall plate jacks (i.e. if you plugged a TV into a coax cable at the headend, it would overload the TV's input section).

Combiners work great if you're simply adding a bunch of signals together that are all the same level (often a rack filled with separate modulators used to build an entire TV channel lineup from individual inputs). What you'll likely need to use is a directional coupler to insert the signal into the CATV feed, but you'd need to know the isolation value required to ensure it matches the signal level of the in-house modulated signal with that of the existing CATV. Unless you already own the correct test equipment, it likely won't be practical for you to measure that yourself. A local AV contractor would likely be needed for that part of the job.
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Jesse Prater

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Re: "Internal" cable broadcasting equipment
« Reply #5 on: January 12, 2015, 05:06:05 pm »

We used the Channel One system when I was in high school (yes, more than ten years ago) in much the same way you describe. I wasn't allowed to look "under the hood" but we had a big silver box that housed a VCR and what I assume was a DA. There were a couple switches to start/stop broadcasts that turned on all the classroom tv's. There was an OTA antenna on the roof that fed local channels through the system.

Now, we don't have a local channel 3, but if you have something like we had, what you want to do is filter out channel 3 from the cable company and feed it directly into the existing headend as others have mentioned. This will let you retain the ability to remotely power on/off the tv's and the default channel (3) will still be your broadcast. It's also the cheapest/easiest solution.

If they want to retain the local channel 3, I'd suggest remodulating it to another channel which would require a tuner/modulator/combiner in front of the Channel One equipment.

If you look around on eBay, there can be great deals on equipment like this that's barely used.

That said, I'm an audio guy. None of this may apply to you and and may be terrible advice.

Sent from my Nexus 5 using Tapatalk

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Chris Clark

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Re: "Internal" cable broadcasting equipment
« Reply #6 on: January 13, 2015, 04:56:42 am »

That said, I'm an audio guy. None of this may apply to you and and may be terrible advice.

I too am an audio guy, I just happen to be one of those Jack of all trade types where I know enough about computers, networks, video (primarily cctv but some broadcast stuff), radio broadcast, etc... And to top it all off, I actually went to school for telecom! Thus how I get "dragged" in to help by my sister. (It's not a bad gig, just a free one... though she usually buys me lunch and dinner when I'm helping, so I guess its not completely free)

I know enough about signal flow and level drops to know that the signal from the cable company will be lower than the signal fed by the modulator. I did see a "directional splitter" that claimed it could be used as a combiner in reverse, which had a 1dB loss from one side (I would put this to the cable company) and a 9dB loss from the other (I would put this to our modulator). What would be the risks involved with sending an unbalanced signal like that to the TVs? Would it just increase the possibility of bleed-over into adjacent channels or could it actually damage the system? I would be putting a channel filter on the cable side of the split, with a purported 60dB nominal drop so we didn't feed back to cable.

Jesse, the goal is to get away from the C1 system since it is no longer serving much purpose other than modulating, and not even doing a great job of that anymore. Also, our wonderful local cable operator put our local PBS station smack dab in the middle of channel 3 (better than being off-center, I guess lol), which would be one of the more used channels if we could, so another reason we'd like to get away from blocking that channel. Anywhere from 25 to 70 appears to be unused according to the lineup, but I know my sister who also has basic cable at her house actually gets up to 70 - I know it depends on the capabilities of the filter the cable company placed on the line so I don't know for sure they don't get them but they also don't look like channels a school would use, so ideally we'd go in there somewhere.

We're not even sure the remote on capability works anymore, the teachers turn on the tv's every morning for the announcements and then can turn them on as desired for the scrolled messages at the end of the day. I thought about trying it the last time I was there (over break), but the idea of then having to go to 40 different rooms and turn them all off (since there is no remote "off" thing) made me decide against even trying it. Don't think it is something they'd ever use.

I may very well open "the hood" next time I'm there to see what if anything can be changed or salvaged, as I'm pretty sure at this point Channel One has forgotten it even exists.
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Alex Donkle

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Re: "Internal" cable broadcasting equipment
« Reply #7 on: January 16, 2015, 03:01:17 pm »

No real danger of damaging TV's if the signal is too high or too low. If the signal is too high the TVs will distort when you try to view the channel, and it'll potentially interfere with adjacent TV channels on the cable. The "directional splitter" you're describing sounds like a mis-labeled directional coupler. Think of them like an off-ramp or on-ramp of a large interstate, they can be used to split-off CATV signals while the main trunk line continues on, or can be used backwards to merge uneven signal levels.  A splitter of any kind in CATV is always just a combination of 1-to-2 splitters, with ~3.5dB of loss on each leg.

The setup you're describing sounds accurate though. The 9dB loss on the 2nd port is the isolation value of the directional coupler. You can buy these boxes for any value needed, which is where measurement tools come in handy.
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