Until last year I worked as an AV tech for the local school board (I am now a radio Engineer). Iwas responsible for the CATV distribution
system for over 21 buildings and worked on nearly all of them during my 5 years there. There are dozens of things that can cause a "low Quality Signal". If you had access to a CATV signal
meter (or spectrum analyser) your job would be much easier, without one you are working
blind. Who in your school district is responsible for the CATV systems within the schools? In MY state (VA) the Public television station would work on them, for a fee of course, but very reasonable, they were doing this before I got there and for my first year I would work along with the field engineer they sent out. eventually my skills grew, and the budget at said station grew smaller, the field engineer became the chief, and only engineer (downsizing) and thought they still did the work, the backlog was great.
the cable company can also be your friend, or a school officials friend. In our county the cable company depended on a franchise agreement with the county which got us things like access to their fiber
network for our inter/intra net, and some repairs would be done as a courtesy. some buildings even had thier hardline run inside, and they pretty much had to work on those because the tools are very expensive.
some questions:
Does it look bad everywhere? this can help isolate problems if some rooms are good and some bad, you may have a failed cable or device on one
leg of the distribution.
does the Cable TV signal look bad also? this will help you know if the problem is with the in
house signal chain. If everything else looks good, look ath the chain from the modulator to the combiner. If it is all bad you should start looking post combiner.
did it ever work right? I worked on systems that were very old and ones newly installed that did not work right and could not ever work right because they were improperly designed. these can be a nightmare, it helps greatly to know that the
system is capable of working correctly. if it did, di some thing change since it was working?
Are there
channel elimination filters on the incoming CATV feed to eliminate the
channel you are broadcasting on? A well designed
system will use these even if the
channel is/was vacant. I have had interference coming in on an empty
channel cause problems with in
house broadcasting. I have also had cable company
channel reassignments cause problems when a previously empty and unfiltered
channel was populated by the cable company. these filters are often left out or eliminated from proposals because good ones are very expensive.
Barring that some things that may help:
Splitters and taps can fail.
amps can fail
The cable itself can fail and allow interference in or make a poor connection.
A signal that is too hot (high) will look mostly like a signal that is too low, so do not assume the signal is too low off the bat.
The modulator should have a
gain knob on it's front panel, you can
play with this and see if it improves the signal, though they typically only
attenuate 20 dB and you will have 40-60dB
gain out of that modulator. there will also be other settings but you really can not properly set any of them, even
gain, without a signal
level meter.
i'm sure there are other things I am forgetting, but basically you can start from the hints here, but your job will be very difficult without the signal
level meter, the one I had on that job was over $800, and the cable co. guys all said it was a toy.....theirs were about $1600 or so I think...
good luck and don't be afraid to get some help.
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