coaxial cable runs ?

Discussion in 'Computing and Networks' started by Mathematics!, Apr 4, 2014.

  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    I am curious in tall buildings where TV coxial cable jacks are installed on different floors how/when do they amplify.

    For example
    Say I was on floor 8 and wanted TV access how can the signal reach me if I am 1000 ft away or more from the main coaxial cable line from the service provider on the first floor. As well as spliters being an issue in the signal loss.

    For example where/when/how/why would you install a signal/voltage amplifier for the coaxial cable system.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
  3. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    yes but I would imagine that eventually the length of the runs and the number of splits ( to different wall jackets )

    Would be an issue even if the signal loss was very low on each of the spliters used.

    Think of empire state building tall I would imagine the top floor wall jackets would have alot of signal loss from the first floor wall jackets.
    The cable length and number of splits for this type of large building seems to much to fix with just spliters and longer cable.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    They also use different types of coax cable.
    For very short distances they can use coax-12, wich gives an attenuation of 12 dB at 100 meters.
    For longer distances they can use coax-6, wich gives an attenuation of 6 dB at 100 meters.
    For very long distances they can use coax-3, wich gives an attenuation of 3 dB at 100 meters.

    You can also have a look in the links of this page:
    http://www.epanorama.net/links/videobroadcasting.html#cable

    Bertus
     
    Last edited: Apr 4, 2014
  5. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    Do they sell the different coaxial cable at local stores.
    I only see RG-6 , RG-59 based cables in home depot or lowes ... maybe there is more of a selection at a electric supply company. Because with just these cords I am left scratching my head on how to make longer runs with out to much loss of signal. Useing these couple types of cords I would need to have a signal amplifier install.

    As for the ratings for length of runs / SNR db for the different coaxial cable I only have a couple choses at a home depot...

    For spliters I can find different rated ones

    So are you saying I am missing a large portion of the coaxial cables being used in long house runs / huge building runs?

    Normally do big buildings just uses spliters and different rated coaxial to make the longer runs with no need for amplification of the signal because I still find it hard to believe that no amplification is needed for a building the size of the empire state building.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
  7. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Start with the idea that one millivolt of signal is considered very good amplitude and 300 uv is acceptable, most of the time. If you amplify the signal to a whole volt, how many decibels can you afford to lose in 100 feet from the outside wall at ground level to the 8th floor?
     
  8. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    I would say the difference in db from 1 millivolt to1 volt would be 30db.
    10log(P2/P2) = db <--- Though I am not sure if there is a difference between sound pressure , sound voltage , and sound power and if they can be substituted in this equation the same. I do know sound pressure is the square of the power if the resistances is the same it cancels out.

    So P1,P2 (power) is interchangeable with p1,p2 (pressure) for this equation.

    20log(p2/p1) = 10log(P2/P1)

    voltages is not a force but more like a unit of force per charge is to me it is more like a unit of pressure. But then it is the potiental energy difference between to point is it can be in this case a force.

    So I am a little confused for electrical measurements is electrical pressure and electrical force the same thing ... They are measure the exact same unit of measure the volt ?

    And electrical current is by definition the amount of electrons that flow per second (C/s)
    So kind of curious about if water current or an non electrical based current can be measured with amps. I guess if you found out the equivalent gallons for coulomb one could put water flow interms of electrical flow (or for that matter any non-electric media)

    But my many issue is the difference between electric force and pressure they are measured the same volt ? But in non-electric media pressure is = F/A. So shouldn't electric pressure be Newtons/Area and electric force be Newtons. How is volts unit both ????

    For what I googled common db ranges for people to hear for common reference is


    • A typical conversation occurs at 60 dB – not loud enough to cause damage.
    • A bulldozer that is idling (note that this is idling, not actively bulldozing) is loud enough at 85 dB that it can cause permanent damage after only 1 work day (8 hours).

    • When listening to a personal music system with stock earphones at a maximum volume, the sound generated can reach a level of over 100 dBA, loud enough to begin causing permanent damage after just 15 minutes per day!

    • A clap of thunder from a nearby storm (120 dB) or a gunshot (140-190 dB, depending on weapon), can both cause immediate damage.


    So I am still find it difficult to determine what 30db is equivalent to and how far before you lose that much sound level or SNR.

    There is to many factors and I haven't figured out a good way to analysis all of these even SNR is different then sound level so could be on a different DB scale as well depending on many factors


    O wait I imagine could look at it like this 1 volt on a 18gage coaxial wire how much voltage drop per foot then compute the total loss from ground floor to 8 floor . And if the millivolt range is exceptable then it should be ok...
    But The I am considering there is a difference between voltage drop and the actual signal /noise in general is different... Would it be safe to say the voltage drop is directly proportional to the sound level heard out the speakers...

    But when it comes to the actually different non-sound frequencies and NTSC/ATSC modulation I would imagine the amplifying the voltage is not only the issue you would have to amplify the signal itself /filter noise (unless amplifying the voltage will amplify the signal and you won't have to worry about the noise over length affecting the quality)

    Forget that for same sound power in different frequencies don't even sound the same loudness so the DB scale is different for different sound frequencies and probably for the electromagnetic waves frequencies as well confusing and to many factors to calculate. Specially in different environments I wouldn't believe there is a general formula for it all. Maybe a case by case based formula for common situations like running TV wire a distance and the signal amplification when and why?

    Probably this is more done by test equipment and then from there a formula is made or derived approximately
     
    Last edited: Apr 6, 2014
  9. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Sound level changes are not involved in the signal level of a TV cable. The loudness at the speaker will be the same, as long as there is enough signal for the TV to work with.
    Any extra signal voltage is discarded by the automatic gain control in the TV.
    The noise level is attenuated by the same amount as the signal level while it is inside the cable, so the signal to noise ratio doesn't change, either.

    Anyway, the answer is 30 db.
    30 db of allowable loss in the cables and splitters.
    Unless it's 60 db. I always get confused about whether it's 10 log for power and 20 log for voltage.
    The point is, there is a lot of room for loss in a TV cable system, even if you only have 1 volt to start with.
     
    Last edited: Apr 6, 2014
  10. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    Show you should never need to amplify it in any building ?
     
  11. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Never, ever, anywhere? Are you nuts?
    The fact that there is a lot of room to play with doesn't mean never, ever, anywhere, no matter what else happens.
     
  12. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    Yes your right I would imagine I wouldn't need to ask this question if I ran wires enough in different places and for different lengths. The theory isn't so useful for this situation

    Telephone lines and data cables I would imagine similar
     
Loading...