Modulator question

[admsjas]

i was going to post this under video conversion but not certain it was the right area. i'm designing the video for our church building project. the offices will have both cable feed and service feed. the service feed will be delivered to a kitchen in our gymnasium, a nursery, foyer, and offices. i was considering a blonder tongue modulater for anything but ch's 3/4. question is could i just get any modulator that will send a signal on whatever ch i select and be ok? my concern is when i combine basic cable service and service feed from auditorium there will be a corruption of either signal. we currently have comcast basic cable with just the little converter box that modulates on 3/4. will combining signal in offices corrupt either way? what is the best solution? appreciate any help in advance

jason

[nic2k4]

If I get this right, you want to distribute Comcast + a modulated camera feed throughout the building. I'm assuming you want to distribute a RF signal. Are you planning on having one Comcast converter box in each room or only 1 for the whole setup? Is this digital or analog cable? Analog cable could interfere with a modulated signal on CH3/4. If there's only one converter for the building, then you can set both modulated sources to a separate channel, but all the rooms will be watching the same show.

Things to consider, you'll need a RF combiner to get both sources onto the same cable. If the cable is too long between a source and combiner, you'll need to add a drop amp at the source (you can tell by the picture quality, it might look washed out, have interference or not come in at all).

Any old RF modulator will work to convert the camera feed, but if the cable run to the combiner is over 12 ft, you'll definitely need a drop amp right after the modulator. I don't know what's a blonder tongue modulator, but to send a RF signal to many room you need to use a distribution amplifier. I use a Siemens VM3x8AB, it has 3 inputs (cable + 2 for CH3/4) and amplifies the signal by 15db on each of the 8 outputs (doesn't work with OTA signals).

Siemens stopped making them and judging from the number of brands that look identical, they probably sold the division (a number of times). Ebay has them and I've seen a Leviton branded one at Home Depot and a Nutone at Lowes.

[jman98]

nic2k4 - Blonder Tongue is a maker of audio/visual equipment. The OP's decision to use all lower case in his post (it beats all caps for sure, but still...) made it difficult to understand that.

[edDV]

OP intends to build his own internal NTSC cable system with cable box/DTA feeding Ch 3 and or Ch 4, then adding additional internal channels with modulators + combiner. This is typical equipment found in hotels and hospitals.

[nic2k4]

nic2k4 - Blonder Tongue is a maker of audio/visual equipment. The OP's decision to use all lower case in his post (it beats all caps for sure, but still...) made it difficult to understand that.

Makes more sense that way, thanks.

[admsjas]

i guess i need to clarify a couple things. sometimes it's hard to convey the picture in your head so everyone else can see it. each office has 2 coax runs to it. 1 for the internal feed the other for comcast which will get a converter box, (yes it's digital cable). so the signal will be combined at each tv that needs it. my concern is will combining in this way interfere one way or the other or not at all. i'm considering a Blonder Tongue or any "programmable" modulater to get away from ch 3 which is what the comcast box is on. the internal feed will have announcements and show the service in areas where volunteers are obligated and can't be in the sanctuary physically (nursery, kitchen, etc..). am i on the right track, does someone have a better suggestion? price is a factor i figure i can get a good modulator for around $75.

thanks, jason

[nic2k4]

So, you're taking the RF output from the Comcast box and feeding it on Ch3 to the TV and you want to modulate the camera feed, from the service, on a different channel?

It's still not clear whether you'll have a Comcast converter box for each TV, but in any case, if your cable TV source comes from the cable box RF out (Ch3), any good modulator with a switch for Ch3 or 4 will work no problem. Modulate the camera feed on Ch4.. You'll need a combiner with two inputs able to handle 60 to 72 MHz each. Set the TV to Ch3 to watch Comcast and Ch4 to see the service.

Cable and NTSC signals use the same frequencies, the modulation is different. There are some gaps in the channel usage, but it's hard to say what Comcast is not using. You're more likely to run into interference issues, trying to combine the Comcast signal directly with the internal feed.

Just curious, are you planning to run a trunk line with taps or distribute cable drops from a central point? Here's a nifty attenuation chart I like to use to calculate how much amplification I need in a setup.

[Cornucopia]

Sounds like you could also go the route where you use an RF A/B switch and both lines go into an input with output going to the tv. A bit low tech, but it should work. And that way, you might be able to always keep the tv on ch3.

Scott

[admsjas]

@nic2k4, each tv will get a converter box but there only like 2 of them. my distribution is as follows: video signal will leave a video switcher, go to modulator, split out of modulator with one run going to a tv that sits on the other side of the wall of the control room, the other feed goes to the secondary mechanical room and will split 5 ways, 1 to guest quarters, 2 to pastors office, 1 to secretary office, 1 to main mechanical room, from main mechanical room it will split 3 ways, one to nursery and 2 to our gymnasium. after explaining all this i'm thinking i'll need a amplifier or will a higher end modulator be strong enough to feed all this? i have a cable amplifier that's not that old (2-3 yrs) if that would work.

[nic2k4]

You will definitely need amplification somewhere along the way and unless you have an amplified modulator, it would have to be at the start of the run. You need to calculate the signal loss through the length of coax and the splitters to figure out how much amplification is needed and where.

You are basically describing a trunk line setup, you would normally use a larger cable than RG6 for the trunk and use taps (not splitters) to bring the signal to each locations.

[admsjas]

You are basically describing a trunk line setup, you would normally use a larger cable than RG6 for the trunk and use taps (not splitters) to bring the signal to each locations.

Unfortunately that means money so I just have to do the best with what I got. I know for a fact they're not going to get RG-11 & taps. I figure if I need to I'll just amplify it as needed.

So what kind of modulator, suggestions anyone?