Those old TV modulators...

Discussion in 'The Projects Forum' started by Externet, Apr 25, 2015.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    There is better ways to do it, but as I have several of those canibalized from old defunct equipment, I was wondering if a channel 3/4 modulator with a proper ~60MHz antenna at its output could put on-the-air a signal.

    The point is to feed audio/video to one of those analog TV channel 3/4 modulators and receive within a small house, the audio/video on channel 3 of an analog television.
    What is the power they put out ? A few milliwatts or not even that ?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I'm not sure the signal will propagate. As I remember them they connected directly to the antenna terminals and allowed text display or games. It never occurred to me to try and make a distance record with one.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    If you couple it to a rooftop TV antenna (array of Yagis) you could probably get some distance though as Papabravo indicated, not much. There is also the legal aspect to consider: Many counties have very strict rules or law about transmitters, particularly on broadcast bands. If you cause interference, you might find somebody ringing your doorbell (neighbor or government official -I had both in the early years).
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    Prior to 2009 I would have been more worried. In that year, in the US, there was a transition from Analog TV to Digital TV and the VHF channels were supposed to go dark. I can't actually find any definitive statement about that situation, only what is supposed to have happened.
     
  5. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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  6. crutschow

    Expert

    Mar 14, 2008
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    Yes, I think you would need to add an amplifier to get any significant distance.
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Many years ago I tried using one of those to do the same thing but I added a vacuum tube amplifier of sorts to it.

    I had very little understanding of how RF tube amplifiers work let alone how to properly design a VHF tube amp but through enough trial and error I was able to get mine to transmit a usable signal about 10 feet.

    Given that I would say that with a properly designed VHF amplifier behind it yes it's doable.
     
  8. RichardO

    Well-Known Member

    May 4, 2013
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    ... but probably not legal. Of course, if you don't interfere with your neighbors who's to say.
     
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Probably won't even interfere with neighbors anyway being what he would be transmitting would be the old style analog signal and not the new digital one so unless his neighbors have their TV's programed for either of those channels and set for analog signals on those channels they will never know his transmitter exists.
     
  10. izon

    Member

    Mar 17, 2013
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    Maybe you just want to use stuff you have on hand but otherwise there are ready made devices to transmit A-V signals (converted to RF)
    a distance of maybe 25 to 50 feet or more depending on surroundings. The receiver end needs to be connected to AV inputs on TV or if not available, use that RF modulater you have to convert to Ch 3/4. I've had pretty good success with a type like this but are subject to interferences from other devices using 2.4gig... (cordless phone, etc)
    There are many types on the market... here is one on Ebay.... even has IR capability if needed.

    http://www.ebay.com/itm/2-4GHz-4-Ch...949dbd&pid=100204&rk=9&rkt=29&sd=181695322259
     
  11. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    US FCC desired same, TV broadcasters / NAB lobbied against and won.
    http://fjallfoss.fcc.gov/ecfs/document/view?id=7021341043

    The FCC had incentives to move to VHF after the last spectrum auction.
    http://www.wileyonmedia.com/2014/01...for-broadcasters-in-the-tv-incentive-auction/
     
    Last edited: Apr 26, 2015
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