Recycle Those Old RF Modulators

[Shadow] sent in this handy idea. For many, it’s sort of a captain obvious hack, but I’m hoping that this might keep a few of these things out of the trash. He needed to send video around the house from a media PC, and happened to have an old XBox RF modulator sitting around. He popped it apart and located the audio and composite video inputs. To get the signal to the rest of the house, he plans on installing a distribution amplifier that’ll amplify and split the signal to each TV set.

23 thoughts on “Recycle Those Old RF Modulators

  1. Simple, but brilliant. Does he have existing cable serice, and wouldn’t this mess it up? If not, can you use 2 diff feeds at once? (eg: 1 modulator on ch3, other on ch4)

    Rather than hack up a RF modulator, many old vcrs will do this for you without any hacking – Yes, I know its less fun…

    I have this “Philips Channel Plus” thing (No model #) which seems to take in a cable feed, and split it into a vhf feed and a uhf feed… What can I do with it?

  2. @1: Is it a UHF block converter, perhaps? They were used to convert some of the high-VHF cable channels (14 through about 30, I think) to UHF, for non-cable-ready TVs. They were just an oscillator and a mixer, really. Not sure what it would be good for, although if you can shift the oscillator frequency to a different range it might be useful for receiving amateur fast-scan TV.

  3. problem I can see is that unlike modern VCRs and sat boxes, the game console modulators always seem to be VHF ones, and since they are double sideband they crap all over the channel below it as well. Poor filtering means they cover 3-4 channels sometimes so mixing in with a feed will not work very well.

    If your happy only seeing the media pc or whatever at the other locations then it will be fine however. Just watch the RF leakage from it if you use a grunty dist amp since you dont want close by neighbours to be able to see what your watching if its…. somewhat adult oriented ;)

  4. wonderful! I also have a similar device lying around somewhere. And I was also planning to do the same thing with it. The device works perfectly with a normal composite input, although it only creates sound for the right speaker, so the left speaker is always dead.. I’m planning to get it conencted to the antenna connector under my desk. The cool thing about it is, that our neighbours and we use the same antenna, so if I feed in a signal my friend in the house next door should eb able to see the stream as well. I also found an amplifier with two outputs. It’s so strong that if you connect a normal telescope antenna to it and one to your TV-set, that is about a meter away, you get a perfect image on the tv. As we don’t have cable it shouldn’t be a problem to feed the video signal to the antenna cables in our house. The only problem might be that the antenna on the roof *could* send the signal to other houses, too. But… who cares :D

  5. schnulli: the FCC thats who.
    Operating an unlicensed transmitter that interferes with a licensed one will get you in trouble.
    (If your neighbors normally get a channel in the area 2-5 that gets noticeable interference you could be subject to fines etc.)
    As always IANAL YMMV etc.

  6. Thanks for your comments guys. Just a little add-on, the scope of this project was to get what I want whilst not spending much (any) money, the quality is not brillant nor ever will be. Schnulli, I wouldn’t worry about the signal making its way next door or up the antenna as the antenna is not hooked into the output of the modulator or amp. Anyway thanks for looking, I’ll have some real hacks up soon!

  7. I wouldn’t worry about the signal leakage too much. Just keep your fittings tight. The modulators do drift some, so you will screw up ch2 or ch4… depending on where you live, hit up a passing cable man and ask if he has an old filter on his truck. A lot of cable companies used to have ch3 filters for movie channels. 4tv’s…I would get any higher than a 15db amp or you’ll risk overdriving the pic..

  8. I’ve been sending video and stereo audio from a Tivo, an MP3 media player and a DVD player over cable for many months using this:

    Even though this digital modulator can transmit on UHF frequencies unused by my cable company, mixing the cable signal and the modulator output has not proven successful. (I’ve yet to aquire a band-reject filter to try.)

    Using various amplifiers and splitter/combiners never produced the desired quality.

    I had an extra cable run back to my wiring closet so ultimately I added this A-B switch:–pi-2049643.html in the wiring closet to choose between the cable feed or the locally modulated signal.

    I use a combination of IR-to-RF and IR-over-cable to control both the A-B switch in the wiring closet and the other devices from the entertainment center, all with a Harmony remote. The remote control is even smart enough to negotiate triggering the A-B switch in the right direction depending upon the chosen input.

  9. I’ve been thinking about doing things like this for a while, but I’ve never figured out what would be required to do this. The problem is we have a bunch of cable boxes with mostly encrypted digital channels, so I’d have to set up a filter on one of the analog channels that no one watches.

    Anyone planning on making cheap device like this that can transmit digital TV signals?

  10. @Schnulli: you can just stick in a few diodes and you’re sure not to mess with anybody next to you. Some catv spliters even do that for you … if not you can get a one way filter/

  11. This is completely unrelated, but I’ve attached an antenna to my cable-tv feed so that the FM radio also in the line is broadcast around my house… Works great.. wonder what the cable guys think about it!

    I’m surprised that it doesn’t interfere with my cable internet somehow, allowing interference in the line and all..

  12. I guess I haven’t been keeping up with the times, don’t VCR’s and the outboard modulators for DVD players still use VHF? I was unaware any of the modulators for TV used double sideband as apposed to vestigial sideband. I have noted while they and be received on an adjacent channel, I have never seen them occupy 3-4 channels. Not that I’m saying the consumer goods are CATV quality. Nor that are they good enough to use 2 to feed 3 & 4 to the same system
    atrain; I wouldn’t have a clue what your device is. In that it has a UHF output, I doubt it is UHF to VHF converter. In the event it’s an active (powered) device, perhaps a RF amp that splits the output? Otherwise a simple signal splitter.

    Orv; In areas where their is Amateur TV activity those uses the ntsc standard cable ready television can be used to receive it.

    Shadow; While it took 2 looks at the block diagram, I understood the antenna wasn’t for transmitting.

  13. i did this way back in the day with my apex dvd player and a sega genesis rf adapter and a tv with no composite inputs. you had to have the genesis ON to play dvds. (or i guess a 9 volt battery woulda workked) i just installed a switch to swap the vid signals out for dvd/sega. i ran all the audio through a component amp anyways so that was no biggie. HA! how many people actually bought one of those convertor boxes to do this?

  14. I seem to recall that when I was 15 I read that the modulators (specifically the type used in spectrums with rf output) can be simply modified to use as a transmitter by removing a few components. They only had a range of say 20m or so, with the right aerial but it would cut out the cable going from the modulator to the tv’s. Since it is such a low power I doubt the FCC would ever pick up on it.

    I now work in a sportsbar and all of their distro for the tv’s at the tables (16 in total) is done using 10 rf modulators all hooked up on the one coax line feeding each tv – one for each source, and it works pefectly. I believe the signal is split using a 16 way rf amp.

  15. Just a short comment about your warnings regarding the fcc:
    I live in Germany in an area where TV con no longer be received via an analog antenna. They have stopped analog transmission about half a year ago. You must now use DVB-T, cable or sat. So it should not be a problem feeding the signal into the antenna cable. But I’ll test with my TV and a normal antenna if you can receive the signal over the air or just through one of the connectors, before I make the system permanent.

  16. This would be great to use for a baby monitor. You could have the babycam feed on all the tv’s in the house. I’m trying to figure out how to do this and not upset the wife by screwing up the cable feed. Can’t interrupt American Idol. Anyone have a link to someone setting this up?

  17. Its been awhile… Anywho for anyone not affliated with the FCC, I have been using a (newer) modulator , hooked into a battery powered amp and a custom diretional antenna as a means of displaying A/V from my laptop, as many of the bars & pubs in my area still use the old loop antenna’s on their tv boxes. Its a matter of finding a close seat and tuning though. Though naturally I don’t recommend trying this, but it brings hours of enjoyment, much like tvbgone.

  18. I have done this with my Tivo for years. I ran a second coax cable to each device in addition to the antenna and have A/B switches so we can watch Tivo or regular tv (regardless of what tivo is recording) anywhere in the house.

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