rf modulation for 'live shot'

[brians0105]

This may not belong in the VT area, but I don't know where else to post.

We use a VT4 to broadcast high school announcements to each classroom using coaxial cable. Our live show is modulated on channel 3 and all 100+ tv's broadcast our show each morning to the students.

We are trying to come up with an easy solution to do live shots from places throughout the school. At the moment, we run a single coax through the halls to our live shot location and feed back the audio and video modulated. We then demodulate it and feed it into the VT and audio mixer.

I was wondering if there is any way we can just use the cable that is already run to each tv in the school. For example, our show is broadcast on channel 3, and we use channel 4 for our live shot return feed.

I have already tried this, but when we are broadcasting on channel 3, the channel 4 reception is not usuable. I don't know much about rf moduation, so help fill me in!

Any ideas would be appreciated!

Thanks!

Brian

[wvp]

the two channels are to close to each other - this is why you never see channel 3 & 4 broadcast in the same area. Your RF modulator allows you to choose 3 or 4 because some areas have a TV station on channel 3 while others use 4 (all of that changes in 2009 btw).
RF is the lowest quality signal you can use. A better solution would be to get some passive baluns and use Cat5 or Cat6 cable. You can get these baluns with RCA video & audio or SVideo (Y/C) & audio for better video quality. You put one at each end and plug however much Cat5 cable you need. I have used these many times with 100' runs and couplers and done at least 550'.

[animlab]

Your project is a bi-directional broadcasting project. I have been doing same thing on mt boy's primary school two years ago.

You can not mix multi-channel RF signal into a coaxial cable without a RF mixer. Following diagram is the one I used in school broascasting, using two cables for bi-directoinal program. You just cannot mix two channels of RF signal without care, they will scramble ecah other.
49142

Or, you can use the wireless video transmitter/receiver for the video send back from classrooms. There are lots of cheap wireless video transmitter/receiver (using 2.4GHz) that cost around USD$200-500 (from 1Watt to 5 Watts power that can send signle from 100m to 2km).

[animlab]

BTW. I agree with Jeff about the quality of RF signals. Wireless video seems a little better and convinent but I experienced single glitches from time to time last time I use it. (They were cheap solution. I do the project free for school.)

I also recommand the Cat5/6 solution if your other camera location is not too far from your control room and if cableing is guaranteed safe (for both children and your equiptments). I have experience that a child was tripped by the long cable and broke his arm bone.
Safty is most important issue than anything else when you shoot in scheel.

[brians0105]

Thanks! So I am gathering that there needs to be a second path for the return video, whether it be another cable or a wireless link.

Unfortunately, the school is very spread out with hallways hundreds of feet away from the studio... and multi-story halls.

It looks as if we will need to stick with our current setup of sending an extra cable run to the remote classroom for now.

So next scenerio... I have only experimented with Cat5 wiring with a product we purchased from Pizazz. If I were to build my own Cat5 solution for this project, could I do the following:

Cat5 Wires 1-2 Video from camera to control room
Cat5 Wires 3-4 Audio from remote talent
Cat5 Wires 5-6 Return video from control room to remote talent monitor
Cat5 Wires 7-8 Return Audio for remote talent IFB/earpiece

Would something like this work over a single Cat5 cable?

Thanks

[wvp]

While that might work you may want to think about the following:
-- running at least 2 CAT5's (one for send and the other for the return) and then you have a backup if one cable breaks.
-- this will also allow you to use standard baluns (I don't recall seeing baluns with 2 video & 2 audio)
-- seperate cables will also give you an ability to use Svideo for your send
-- you might be able to get students to run cable and maybe even make connections for the install
-- you could run the cat5 to jacks in the halls and then just plug in from there vs. putting connections in each room. Of course if you can get the approval running 3-4 cables to each room also gives you ability to send a higher quality signal and can easily be adapted for other uses.

[PIZAZZ]

catching up on the boards while we drive from San Diego (Siggraph) to do WEVA in Vegas next week.

Brian,

It would be possible to do what you ask via a cat5 or better yet a pair of them like Jeff mentioned.

On the other side you might be able to do this with what you have in place already. If you have a run of Coax from where you want to broadcast from back to your distribution point in the studio, you could repatch that cable run from an output to the input of the RF DA. You might need to go through and label all the cables and map their destinations. You would put the RF Modulator with the VT system rack's output and shoot the modulated signal back to the RF DA in the studio. I can't remember if you had a RF DA or j ust a nest of passive splitters. This idea would really only work well if you had home runs from the DA to each room. Most of the time I have seen schools and churches not install home runs due to cost. They end up splitting and splitting and splitting and splitting the signal from TV to TV to TV.

It is worth investigating. You might as well save the time and money installing more cable if you can help it. I could bring one of my RF signal testers when I come up to visit soon.

[brians0105]

Thanks guys for the input. I'll be thinking about our options, but for now we'll stick with our current solution of running a coax line to our live shots. Maybe later we'll work w/ Jef to come up with a cat5 custom solution.

Yeah, Jef, as you can probably guess since it is a school, I believe it is just distributed via a bunch of splitters here and there. The school was wired by Channel One. It's a daily "newscast" for highschool students. They supplied the TVs and all the wiring and one coax cable leaves the studio and it is split here and there for all the classrooms. I do believe there are several signal amplifiers in different locations throughout the school when they added on two hallways.

Anyways, looking forward to seeing you again when you come to visit. Thanks

[vanderwielen]

You can use the same coax. simply turn around a passive catv splitter and inject a modulated signal from the classroom. demodulated at the head end. you might need to pad down the signal if you're too close to channel 3. i'd suggest some unused VHF channel in your area as high as possible. you could simply do this every where in your school...connecting anywhere and have your signal show up at the headed. passive taps are not directional, but do create a loss. this is your cheapest solution.

[brians0105]

vanderwielen, this is what I was hoping to accomplish. you're correct in saying that when i try to modulate another signal on channel 4, the signals corrupt each other.

where could i purchase a modulator that will use channels other than 3 and 4? ebay? what should i search for?

thanks!

[vanderwielen]

here's one that does UHF and CATV:

http://www.smarthome.com/7715a.html

[PIZAZZ]

you could simply do this every where in your school...connecting anywhere and have your signal show up at the headed. passive taps are not directional, but do create a loss. this is your cheapest solution.

It depends on the way the cabling was implemented though. If indeed there are lots of splitters used and they are passive then tapping the local connection "might" work. If there are signal amps inline as Brian mentioned then they may not pass the signal since not all signal amps are bidirectional.

We will better know what the situation is next week when I get to drop by.

[invica]

I'm not sure what your doing with the video and what quality you need, but if your school has a good network, wireless or otherwise, if you have the capability to stream the video shot and then take a scan converter form the receive computer back at your head end you can take the scanconverter signal and bring that into your VT as a video and audio source. It really depends on the quality you want. Going on a local Area Network means you can probable pump your video encoder as highas you can to get the video quality up. The other nice thing is I think even a really cheap scanconverter will do the trick and most of them you can zoom with them making the picture a good size. Just a thought.

chad

[Tarheel Cougar]

Good luck trying to backfeed that. I have experience with Channel One wiring at two different schools done in the early 90's and lets just say it was done as quickly and as cheaply as possible. Splitters everywhere dangling from the ceilings and lying on top of roofs not bolted or secured to anything, LOTS of inline amps (NOT bi-directional), no "home runs," some RF connections were looped through at each TV, overall very dirty. Of course, these were two pretty large campuses (One HS and one MS) with several buildings. Its amazing anything comes through, and at some of the far classrooms, nothing does. At least the schools got free TV's out of it.

[brians0105]

Yeah, Tarheel,

I've done some tests and I am able to accomplish this from some locations close to our studio head-end... however, when I go to classrooms that are physically farther away, I have more trouble. It is most likely due to the splitters and uni-directional amps. Oh well, we know we can do this from certain locations... but for others we'll have to use cable runs.

Thanks guys!

[lvsoule]

I have a couple of RF Modulators I bought from DBLDistributing.com for $6.00 each(not selling). I always have a couple around for our games. The final VCR in our production go to the RF modulator so I can run 1 cord(instead of 2) to the Announcer booth for TV viewing. It will do channel 3 or 4. It works great! Just get an account there and you'll be like a kid in a candy store.