Splitters, Attenuators, Filters, Diplexers, Other Signal Gear - Page 6 - Canadian TV, Computing and Home Theatre Forums

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post #76 of 1739 (permalink) Old 2005-12-20, 02:54 PM
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For the DBS part, if its a single LNB there shouldn't be any problem, but FTA multi-LNB systems need a DiSEqC (pronounced "Die'-sek") switch, which can be really sensitive to line length, injection losses, etc so it might not like being run through a diplexer.
Quote:
Originally Posted by hdtv101
If your going to use an antenna mounted preamp there will be no way to send power from the power supply to the antenna mounted preamp.
Either that or you could locate the diplexer in a place outdoors where you can also mount the preamp's power supply in a weatherproof case with AC power, with its input coming directly from the preamp on the mast and its output and the DBS output feeding into the diplexer and its own line going indoors.
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post #77 of 1739 (permalink) Old 2006-01-13, 01:15 PM
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Signal Leakage Between CATV and OTA - How And Why To Prevent It

If anyone is contemplating running a combination of Cable TV and OTA to the same TVs or receivers, there are specific safeguards you must take to isolate the two signals from eachother. This is not a casual concern, its very important that you do it correctly!

Satellite and OTA into the same TVs or receivers are not a problem.
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post #78 of 1739 (permalink) Old 2006-01-14, 05:24 PM
 
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Would you care to elaborate Stampeder? I have a few friends who have purchased new TV's with integrated ATSC tuners, who also use analog cable (too cheap to spring for HD terminals). What precautions should one take? TIA!
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post #79 of 1739 (permalink) Old 2006-01-14, 05:46 PM
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Gladly! Here is the situation: you have two signal sources that are feeding your TV using essentially the same frequency ranges. OTA antennas feed VHF Low, FM Radio, VHF High, and UHF to your TV, but so do CATV systems, albeit with their own sub-channel maps over the same frequencies. They do not get along with eachother.

This frequency overlap is due to historic reasons because in the 1950s-60s there were no Set Top Boxes yet for cable channel tuning, so the CATV providers had to overlap the regular 13 VHF channels and later the UHF channels with their own signals in order to feed your TV. This is why CATV gear is so heavily shielded to this day - there is a direct conflict with OTA. If we could redo CATV all over again I'd advocate assigning a third range of frequencies apart from TV and Satellite.

So, if you simply connect the antenna and the CATV with a splitter you will cause signal leakage of the CATV signals through your antenna and vice-versa, which will cause garble and interference not only for yourself but for your neighbours too. Connections like that are ILLEGAL. Industry Canada and CATV providers constantly check for signal leakage and will come down really hard on you if you let it happen. The leakage problem does not happen with Satellite because its incoming signals are way off in another part of the frequency spectrum from TV.

What is the solution then? An A-B input switch is one method, or if your TV has 2 coax inputs you could test to see if they are discrete (separated inside to prevent leakage). Some people run the OTA lead right into the TV and the CATV lead into the VCR and then over Composite or SVHS into the TV. There are a few solutions like that if you think about it. I think there might be remote control capable A-B CATV/Antenna coax switches out there too.

Check out previous posts in the OTA Forum by HDTV101 and others about this issue.
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post #80 of 1739 (permalink) Old 2006-01-16, 04:13 PM
 
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Stampeder,

I have a T.V that has 3 inputs. 1 for Direct T.V and then Antenna A and B
I have Antenna B with basic cable in it and Antenna A has OTA. The T.V has built in ATSC . How do I check for "leakage"?

Thanks in advance
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post #81 of 1739 (permalink) Old 2006-01-16, 04:24 PM
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Quick Method of Checking for CATV/OTA Leakage

The easiest way to check for leakage between 2 sources is to disconnect the regular TV's CATV and OTA inputs and put a portable TV with rabbit ears right beside it. On the portable TV do a full channel scan of both TV and CATV and make note of which channels you receive and also which other ones are really garbled.

Next, hook up the regular TV's inputs again and turn it on as well as any set top boxes needed, then on the portable TV do a full channel scan of both TV and CATV. If you are now receiving more channels than the with the first scans on the portable TV (even if they are garbled but strong signals) then you have leakage. If not, your TV is properly isolating the inputs.

Another thing you can do if you're not sure is check your TV's manual or contact the manufacturer to find out if they're isolated.

macker, let us know the make/model of your TV and what you find out.
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post #82 of 1739 (permalink) Old 2006-01-16, 04:43 PM
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RF Modulators and OTA Can Also Cause Leakage Too

Be aware that if you use an RF Modulator to connect a DVD player, VCR, XBox, or other electronic gear to your TV because it only has a coax (RF) input, you must not put your RF Modulator and your OTA connection on a splitter feeding into the TV. If you do, you will cause signal leakage that will mess up everything you try to view and maybe that of your neighbours too. Industry Canada might even fine you when they triangulate in on your location.
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post #83 of 1739 (permalink) Old 2006-01-16, 09:23 PM
 
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They probably don't care as much about interferance with OTA as with other services. Cable channels use frequencies other than TV, including aeronautical band, etc.
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post #84 of 1739 (permalink) Old 2006-01-17, 08:54 AM
 
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Stampeder,

The make and model is RCA Scenium HD65W20. The only info I've found is

"Deluxe Shielded Tuner with 181-Channel Tuning Capability = Check your cable company's compatibility requirements"

So hopefully this means that they are isolated

thanks
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post #85 of 1739 (permalink) Old 2006-01-17, 09:36 AM
 
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Lightbulb paranoia or good intentions?

Quote:
Originally Posted by stampeder
If we could redo CATV all over again I'd advocate assigning a third range of frequencies apart from TV and Satellite.
And what range of frequencies would you choose? (there isn't exactly a surplus out there!) Correct me if I'm wrong, but I think the problem plaguing CATV systems has traditionally been the inability to effectively distribute channels using higher-frequency assignments due to increased signal attenuation. Nowadays, they're getting into super and hyper bands that nearly mimic UHF frequencies, but they can only do this because of the recent feasibility of sending optical fibre signals to individual neighbourhoods and then doing relatively few amplify-and-split coaxial trunks to peoples' homes. In the "olden days", when the whole CATV system was copper coaxial cable from headend to customer premises, it was very hard to maintain all channels at a uniform signal strength, since upper channels attenuate quicker than lower-frequency ones. In other words, this is why crappy, who-watches-that kind of channels were assigned "high" channel numbers since few people really cared that you got a crummy, noisy picture on them.
I tried to look for a decent website that shows all the frequency allotments, but this is all I could find:

http://www.tvtower.com/Commercial%20...equencies.html

Quote:
Originally Posted by stampeder
So, if you simply connect the antenna and the CATV with a splitter you will cause signal leakage of the CATV signals through your antenna and vice-versa, which will cause garble and interference not only for yourself but for your neighbours too. Connections like that are ILLEGAL. Industry Canada and CATV providers constantly check for signal leakage and will come down really hard on you if you let it happen.
Is there really any proof of this kind of heavy-handed action against private citizens? I mean, if someone accidentally spliced their CATV connection to their OTA TV antenna, and started radiating minute amounts of interference into the airwaves, are the Industry Canada goons going to come and arrest you and treat you like some kind of ruthless corporation? I mean, the average CATV drop has what, 0dB signal strength? You might be lucky to cause interference with someone else's reception down the street, but it's not as if you're going to actually ruin the signal propagating from a 500,000 watt commercial transmitter stick hanging 500 feet in the sky.

I'm not saying this is completely laughable -- just that when you talk about actually doing tests to make sure a multi-input TV actually has sufficient isolation between CATV and OTA inputs, c'mon. I doubt the feds would bust down your door for using a piece of consumer equipment how it's intended to be used!
Quote:
Originally Posted by stampeder
What is the solution then? An A-B input switch is one method, or if your TV has 2 coax inputs you could test to see if they are discrete (separated inside to prevent leakage). Some people run the OTA lead right into the TV and the CATV lead into the VCR and then over Composite or SVHS into the TV. There are a few solutions like that if you think about it. I think there might be remote control capable A-B CATV/Antenna coax switches out there too.
Has anyone found a remote-control A-B switch? I've been looking for one that is not infrared, but it seems impossible to find.
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post #86 of 1739 (permalink) Old 2006-01-17, 12:29 PM
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Here's a much better TV frequency chart from Tin Lee Electronics:

http://www.tinlee.com/FreqChart.htm

Also mr.ous, as ShawnD was getting at, and as HDTV101 has some great info on, certain leaking CATV frequencies can directly affect aircraft Instrument Landing Systems due to overlap. Signal leakage is taken extremely seriously in areas near ILS-equipped airports, meaning where the vast majority of Canadians live. Or look at it from the CATV side: some preamped OTA antennas are outputting as much as 25 to 30dB gain through their downleads, so having that bleed into a cable system is really not cool.

So which is better, to inform readers about this topic or to just let it ride?
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post #87 of 1739 (permalink) Old 2006-01-17, 02:57 PM
 
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Red face

stampeder,

I wasn't trying to ridicule your cautionary note. I mean, there's all kinds of information out there about this:

http://strategis.ic.gc.ca/epic/inter.../sf05757e.html

http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/vwapj/tv.pdf/$FILE/tv.pdf

I just took a bit of an exception to what I interpreted as a dire warning. DBS home satellite systems typically convert 11.7-to-12.2 or 12.2-to-12.6 GHz signals from the LNBF to 950-to-1450 MHz ones sent through the downlead to the receiver. I would hesitate to call them "not a problem" -- it's just more difficult, I suppose, to cause 'common' interference problems. If you have one of those in-line satellite booster/distribution amps and don't know what you're doing, you could cause just as much trouble with your local cable company, other radio signals in the airwaves, the feds, etc.

Plug in a spot welder? You cause electrical spikes within the local circuit. Short out your phoneline or attempt to send power down it maliciously/inadvertently? You probably won't blow any of Bell's equipment, since they usually have protection devices in place, but they'll probably send a tech to your door, eventually. Attempt to suck juice out of high-tension power lines by putting massive induction coils in close proximity? You might be in trouble with some hydro officials.

Heh, I guess I'm just saying I'm surprised that increased awareness is being sought, when I'd hope most people eager enough to investigate OTA HDTV would know you can't use a splitter 'backwards'. Maybe it's valid since a lot of people have grown up not having a clue that you can even pick up channels off-air, and so they have very little experience with MATV type systems. Still, some TV sets are so poorly manufactured with respect to leakeage that if you're within reasonably vicinity of an OTA TV transmitter site, you can get better than a total snow image of reception without anything even connected to the 75-ohm antenna jack; that's just the nature of consumer equipment, and I don't see how the consumer can be held responsible so long as they made all the proper connections.
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post #88 of 1739 (permalink) Old 2006-01-17, 04:52 PM
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Disagreeing with me is quite alright, by the way.

cheers,
stampeder
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post #89 of 1739 (permalink) Old 2006-01-19, 02:37 PM
 
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Question Need Advice - CATV and OTA Into Only One RF Input?

Hello from Vancouver. Kudos to all participants of this forum - it is a great resource and one of the reasons I love the Internet.

My HP/Panny PE4200N ED plasma has built-in ATSC/NTSC/QAM tuners but only one RF input. I'm looking for the best solution for utilizing both analogue cable and an OTA antenna signals. If I understand the info provided by Stampeder, an A-B input switch would work. I have a couple questions about this solution:

1) Any recommendations for a good switch that is remote controllable?

2) With an A-B switch installed so that I can select one of either the OTA antenna or the analogue cable signal, is it likely that my TV will retain in its channel memory both the OTA channels and the analogue cable channels or will there be some conflict that prohibits all available channels from co-existing?

The other possible solution is to connect the OTA to the TV's RF input, and connect the cable to the VCR and then connect a composite video out from the VCR to the TV. I have a couple questions about this solution:

1) With this configuration, I would be using the VCR's tuner for the cable channels, right? Therefore, I would not be able to record something on the VCR and watch a different cable channel at the same time, is that correct?

2) Using a composite video cable from the VCR to the TV, is the picture quality likely to suffer compared to the existing coax connection between the VCR and the TV?

If I understand things correctly, a remote controllable A-B switch is the best option - provided that my TV will retain all available channels in its memory without any conflicts (re-scanning channels every time I switched inputs is not a viable option in my opinion).

Thanks in advance for the guidance.
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post #90 of 1739 (permalink) Old 2006-01-21, 03:30 PM
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Gee, I thought people would jump in with advice for you, cohoho... here goes...

First, read up on the various connection types in the DHC FAQs so that you can tell what they are capable of when hooking up components like VCRs. In there you'll see that for VCRs and DVDs it is preferable to use composite over RF.

OTA is a different consideration since your TV has a built-in ATSC tuner, so you have no choice in this matter: you must run the OTA antenna coax lead directly to your TV's RF input since it is going to be inputting ATSC (HD 16:9 DD5.1) signals to its tuner.

Then I would run the analogue CATV lead into the VCR since it is going to be inputting NTSC (SD 4:3) and that's what the VCR is made for. Do a channel scan and that will load up all the analog CATV stations you are getting.

Then, based on what the VCR offers for connections, use the best one that it can do. If its composite, so be it, because it is generally better than RF for NTSC programming.

Regarding TV Channel memory, you would use the TV's for OTA, and the VCR's for CATV.

I think this is the simplest/best setup for you since it doesn't require any additional purchases and it gears the signal source to its best medium in your particular case. It also avoids the problem of signal leakage discussed in this thread: http://www.digitalhomecanada.com/for...ad.php?t=36675
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