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#1
08-23-2007, 10:13 AM
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Wireless R.F. Modulator??
I would like to know if the signal from a $20 r.f. modulator can be amplified so that it will broadcast without connecting a cable. I have a collection of small TV's and enjoy watching old B/W movies on them. I want to be able to go to any room in the house, plug in my little TV, extend the antenna, and receive the movie on my DVD through the TV (ch.3 or 4). I have a Gemini Rabbit system that works fine, but I want to eliminate the receiver. Anyone know if this can be done?
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#2
08-23-2007, 10:11 PM
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Back in the late 80's, we took the Ch 4 output from a VCR, fed that to the input on a RF amp and sent that output up to the TV antenna on the roof of the house. With a portable tv we could pick up that signal 100 feet away.
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#3
08-23-2007, 10:58 PM
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Quote:
This thread has been forwarded to the proper authorities. Expect a black Suburban at your door soon. 
__________________
From Captain Video, 1/4/2007 "It seems that Italian people are very prone to preserve antique stuff."
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#4
08-23-2007, 11:22 PM
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I seem to recall hooking just a set of rabbit ears to the output of a VCR and being able to pick it up several feet away.
I'll have to try it again and see if it works.
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#5
08-23-2007, 11:43 PM
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Quote:
It's best if I don't answer how I know that...  
__________________
various stuff
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#6
08-24-2007, 06:46 AM
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It is, however, as some others here have hinted, basically illegal to do this sort of thing, strictly speaking. Back in the 1970's, my first Atari 2600 video game system had a big notice warning me not to connect an antenna and the game switch to the TV VHF terminals at the same time. Of course, I did that right away.  We looked at Channel 3 on my brother's TV in his room down the hall. "Hey-there's Air-Sea Battle!"My ham radio license lets me do things like this legitimately, but on specific frequency bands, and no commercial content or music in our signals, etc. Once analog TV goes away in 2009, especially if few signals stay on the VHF channels, I expect many of us collectors will want to start trying things like this for our old TV sets.
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#7
08-24-2007, 12:15 PM
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They made a wireless sender called a VCR Rabbit with a transmitter and a receiver, but I think it goes on some kind of UHF frequency and gets down-converted back to Ch 3. I don't know if they still make them, but I bet eBay has some.
How about feeding a signal into a BIG apartment building-style Winegard distribution amp? Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10
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#9
08-24-2007, 01:55 PM
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I've been thinking about a cable or MA tv frequency-agile channel modulator that would take A/V inputs. Pass my cable through it and dial up a non-used channel to all the house sets. Even add a channel block if needed for VHF.
Dave A
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#10
08-24-2007, 08:31 PM
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Video Sender
About six months ago I came across an RF modulator/video sender on that auction site. I of course bought a couple of them for test purposes.
 They have left, right audio in, video in, volume adj, bright adj, and an rf out F connector. On the front is a switch for use as a modulator or a video sender, channel adjustment and on the top is a short telescoping antenna. The instructions do say that you should check with authorities before operating it in video send mode. It tunes from channel 2 thru 6 and with the telescoping antenna I can get a good signal at 50 feet, gets spotty after that. I imagine using a higher gain antenna hooked to the F connector rather than a 6 inch antenna would give better results. It does not transmit stereo audio, it simply blends the channels to mono. They were about $30.00 each. Speaking about signal leakage, Comcast is so bad here I can walk around my entire home and outdoors with a scan type color LCD TV and can pick up 30 or so cable channels in between the over the air stations, perfect picture and audio.
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#11
08-25-2007, 12:26 AM
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Glad to see that my question stirred up some interest. Today I removed the amplifier board from an amplified indoor antenna, connected the r.f. modulator thru a matching transformer to the VHF input, and a 4 foot length of wire with an alligator clip on one end to the output. Fired it up and got an acceptable picture and sound about 18 feet away, but it's very touchy as to the position of the wire and the location of the TV. Tried clipping the output to various metal objects and also tried the rabbit ears, but it seems to work the best with just the length of wire.
I am going to keep looking for more antenna preamps at the Salvation Army. My thought is to connect 2, 3, or 4 of these preamps in a daisy chain and maybe wind up with a decent signal that will allow me to move about the house with my little receiver. I also thought about tuning the antenna wire by varying it's length, but I don't know the correct length for VHF channel 3. Also thought about using a variable capacitor. Any suggestions would be appreciated. I want to keep this very simple and low budget. Keep these great ideas coming! Thanks.
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#12
08-25-2007, 12:27 PM
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I am going to keep looking for more antenna preamps at the Salvation Army. My thought is to connect 2, 3, or 4 of these preamps in a daisy chain and maybe wind up with a decent signal that will allow me to move about the house with my little receiver.
I also thought about tuning the antenna wire by varying it's length, but I don't know the correct length for VHF channel 3. Also thought about using a variable capacitor. Any suggestions would be appreciated. I want to keep this very simple and low budget. Keep these great ideas coming! Thanks.[/QUOTE] You may start to overload the input sections of the amps if you daisy chain them, just a guess though. I believe that channel 3 and 4 are down around 40 to 50 megacycles so the length of the transmit antenna should be quite long
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#13
08-25-2007, 02:28 PM
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It would probably be worse to daisy-chain those preamps than to just get one powerful one in the first place, because they are all intended for the same input level, more or less. Otherwise, it is like hooking a stereo amplifier to the speaker terminals of another stereo and hoping to get the combined output of both amplifiers.
If you want to make your plan work, a tuned antenna is very important. The length you want in feet, for a 1/2-wave dipole, is 468 divided by the frequency in megahertz, or just under 7.5 feet for 63 MHz (the center of Channel 3). You could cut two pieces of wire, each about 3.7 feet long, and attach them to the center and shield of a piece of TV coax, then mount the whole thing horizontally, as in the Wikipedia article for dipoles. http://en.wikipedia.org/wiki/Dipole_antenna That should work far better than just connecting random pieces of wire.
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#14
08-25-2007, 05:09 PM
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Back in 1977 or so, in Syracuse NY, someone built the nation's first pirate TV station. "Lucky 7" on channel 7, a usually empty channel in that town back then. Syracuse had only 4 TV stations back then. Anyway, it was said that someone built the transmitter from parts from a guitar amp and it was on the air over a weekend. Everyone knew that the nearest FCC office was in Buffalo NY and they don't work on weekends... They played some Star trek episodes, some porn movies and such...
A short article about this pirate TV station apeared in the New York Times.
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#15
08-25-2007, 08:16 PM
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