Another Modulation/Combining Signal Question

[dddane]

I work in an office with about 40 TV's around hooked up to Comcast analog cable. we recently came across the need to get a single channel that is on comcast's digital lineup. (in reality, though, there might be 2 channels that would be ideal).

The office manager's idea of course was to buy half the lease digital boxes from comcast at $10/mo to get this single new channel. Due to the cost of the boxes, only half or so of the office would get them (but still that comes out to an exta $220/mo) She didn't consult the IT person who might have better knowledge or ideas....

My first thought was some sort of modulator or combiner... a digital receiver sits in a closet where the main comcast signal comes in, then a combiner puts the signal from the digital box back in to the cable feed ..

the question i guess is do I need an RF modulator for this, a combiner, a diplexor, a combination of the above? What exactly does an RF Modulator do (the kind that outputs to channel 3 or 4).. I know it obviously combines the signal onto another cable. Does it block out the channel its using, or would there be some sort of interference?

If the digital box outputs to a certain channel (which presumably can be only 3 or 4, which are "in use"), what is the best solution for this? A combiner (reverse use of a splitter) of some sort would probably not be sufficient since the channel 3/4 is already in use. Does an RF Modulator take care of this by blocking out the channels that are in use?

What does a diplexor do, is this the same as a "combiner"?

Another thread mentioned this product: http://salestores.com/chplsv2sstmo.html ..which seems to be a higher end RF Modulator that is stereo and lets you pick your output channels. I don't mind spending $300 on this if we know its going to do the job. The non-stereo versions are much, much cheaper ($15-20) obviously. If I hooked one of these up where our comcast line comes in, is there any issue or potential that the modulated signal will fade as it goes further away or through other splitters?


I searched around and got some good info but am wondering what the best solution would be... We don't mind spending a little money up front if it means not spending the same money every month on digital boxes.

 

[VinceT3]

What does a diplexor do, is this the same as a "combiner"?

Diplexor combines the signal without merging them. You need another diplexor at the other end to undo the combined signals.

I use a splitter backwards to combine 3 signals into 1 and broadcast that thoughout my home.

 

[dddane]

Diplexor combines the signal without merging them. You need another diplexor at the other end to undo the combined signals.

I use a splitter backwards to combine 3 signals into 1 and broadcast that thoughout my home.

ok thanks for the diplexor explanation.

it sounds like a reverse splitter alone won't do the job to me... and that's mainly because the outputted ch 3/4 from the digital box would overlap with another already existing cable channel on 3/4. so I would need an RF modulator that you can pick a different channel (say... 72). and then a combiner that combines it.

at that point, though, what is the potential for insertion loss or things like that if the signal travels through the office and is split again somewhere.. will the signal fade? also, i keep hearing to use channels that are somewhat isolated (the channels in the area aren't in use). is this a concern if i use a high end modulator like the one i linked to above? do I need an amplifier or an attenuator to deal with this?

i looked at some of the "distribution" systems that seem to modulate and have multiple outputs... the channel plus 3025, for example, modulates 2 signals and combines, then has 5 outputs... the manual says you can't split the outputs at all though.

what exactly makes that one "high end" (other than costing a lot more)... i thought at first it was because it was stereo, but I just found other stereo modulators for $40ish. So is it because you can pick any channel output you want?

thanks again

 

[dirkleearm]

Look up Swiden Distribution, they have modulators I have used a number of times. If you can put it on an unused band just use a backward splitter to combine. Otherwise you will neet to use a high Q filter to block one of the incomming cannels, then combine your added channnel(s).