Creating a Home TV Transmitter

Now that TV broadcasts have gone digital, what is a television collector to watch? Of course, you can hook up a DVD or VHS tape player to watch recorded material on channel 3 or 4. You can also use a converter to watch digital TV broadcasts on an analog set.

I prefer to watch television the "old fashioned way," with a rabbit ear antenna. I also like to use my vintage TVs anywhere in the house, free of wired connections.

My solution is a home TV station. It covers the whole house and can be received by as many old TVs as I feel like powering up.

Let's Have a TV Party!

This impromptu "TV party" shows my transmitter in action. The color set is my restored RCA CTC-11A. The black and white set at lower right is my DuMont RA-103. On top of the DuMont are two handheld TVs, the type which can only receive through an antenna: a Panasonic Travelvision and a Sony Watchman.

All four TVs are receiving through their antennas, from my home broadcasting station on the other side of the house. The content is a live movie from a satellite channel.

The second party features my Sharp 3LS36 mini color television along with the two handhelds. In this case, I hooked up a DVD player to the transmitter.

Many mini portable TVs lack an external input, so if you collect handhelds, a home transmitter offers the only way to use them at all.

Agile Modulator as Transmitter

Setting up this home station was easier than connecting a typical DVD player. The heart is a device called an "agile modulator," specifically a Blonder-Tongue model AM60-550A.

I paid $26 for a surplus unit on eBay. It has ample power to reach the entire house, using a set of rabbit ears as the transmitting antenna.

Connecting Your Video Source

Hooking up the transmitter couldn't be simpler. It has one input and one output.

For input, I often feed the transmitter from one of our satellite TV boxes. You can use any source that produces standard audio/video output: a DVD or VHS player, digital converter, video camera, and so on. Whatever you choose will be broadcast to any TV in the house, on the channel you select.

On the back of the Blonder-Tongue are jacks labeled AUDIO IN and VIDEO IN, where you plug in the audio and video cables from your source device.

Note the short length of coaxial cable connecting the IF IN and IF OUT connectors. My unit came with that cable. If yours lacks the cable, you'll need to supply one. Nothing special is needed; use the same coaxial cable as with any audio/video device.

The VIDEO IN jack is an "F" type. Most video sources will use phono cables. If needed, you can get an inexpensive F-to-phono adaptor from Radio Shack or similar sources.

Connecting Your Transmitter Antenna

Like every transmitter, the agile modulator needs an antenna. I use this funky old pair of rabbit ears. The type is not important. Any cheap antenna from a thrift store or flea market will work.

Notice the little adapter on the end of the antenna cable. This lets you plug it into the transmitter's coaxial output jack. Radio Shack and many other sources sell these adapters for a buck or two.

The next photo shows the RF OUT jack in back of the modulator, where you will connect your antenna.

Choosing Your Broadcasting Channel

The agile modulator transmits on one channel at a time. You pick the channel by setting little DIP switches in the front, following instructions on a plastic card that slides out from the panel.

A DIP switch can be flipped up or down with a pencil point or small screwdriver blade. Flip your switches to match the desired channel's diagram in the chart. I picked channel 5, but you can use any of the standard VHF channels 2-13.

Using Other Modulators

You may already own a modulator that can broadcast a TV signal. If the back of your VCR or DVD player has a connector labeled something like ANT OUT, RF OUT, or TO TV, that will send the same type of signal as this modulator. It will be much weaker, of course, because it is not amplified.

Just for fun, try connecting a rabbit ear antenna to such a connector and playing a tape or DVD. Connect another antenna to your TV and tune it to the same channel (3 or 4) as the player.

You'll find that the broadcast reaches only a few feet. Not a very powerful TV station! However, you might enjoy this if you have two vintage TVs side by side and want to watch a movie on both of them without a tangle of wires.

Legal Transmission Limits

The Federal Communications Commission regulates broadcasts in the radio and TV frequencies. I'm not good at deciphering legalese, but as far as I can make out, a home transmitter's signal strength must not exceed 100 milliwatts.

Since my transmitter doesn't reach beyond our house, I assume it can't interfere with other broadcasts (if any) in the neighborhood. I happen to have an old TV field strength meter, which was used years ago when servicemen installed roof antennas in customers' homes.

I have no way to check this meter's accuracy. However, it was fun to see its needle move a bit when I turned on my home transmitter.

A handheld TV like my Travelvision or Watchman makes a more practical tester for a home broadcasting station. Just turn it on and walk around the house!

You'll find that antenna orientation is very important, for the transmitter as well as the receiving TV. Most homes are also full of devices that create unwanted RFI (radio frequency interference). These include computers, fluorescent lights, big-screen TVs, security systems, light dimmers, electric motors, and so on. If you have bad interference from such a source, your choices are limited. Either turn off the device or move your transmitter or receiving TV away from it.

Handy For Restoration, Too!

I have found my home transmitter very useful when restoring vintage TVs like the RCA CTC-11A and DuMont RA-103 seen earlier.

Restoring an old television means playing it over and over, to check this or that. In the old days, a serviceman could just connect rabbit ears and tune in a local station. But nowadays there are no local stations!

To test the TV on the workbench, you can connect a video player or digital converter box, but that adds to the crowding and rat's nest of wires on your bench. It also limits you to two channels: 3 or 4. What about all the others? Does your TV work beautifully on, say, channel 8, but poorly on channel 4? Knowing that kind of thing might save a lot of troubleshooting time.

When I'm working on a TV project, I leave the transmitter on at all times and connect rabbit ears when it's time to try my TV again. Quick and easy! By changing the transmitter's channel, I can test the TV's performance on any channel.

Receiving a "real" over-the-air broadcast is also an excellent performance test. Vintage televisions were designed to operate in a world of mostly-weak broadcast signals. The signal from a modern device like a DVD player can be quite different.

If a signal is very strong (often the case), it can overload a sensitive old TV, causing the picture to "bloom" and become unfocused or too-contrasty. If the video player is your only source, you might wrongly think that your TV has a serious problem, when in fact it's responding normally to an excessive signal.

Modern video players can also introduce problems that didn't exist decades ago. A VHS tape player may create horizontal smear or bending in the picture. MacroVision and similar copy protection schemes may cause ugly picture interference that vintage TVs can't handle.

This photo shows copy protection interference (columns of colored lines) on my CTC-11A. There's nothing wrong with the TV, as we saw in the earlier Shrek photo. The lines are caused by extra copy-protection information in the video signal. Such information didn't exist when the TV was built in 1961, so it causes garbage on the screen and buzzing in the speaker.

(An inexpensive video stabilizer will allow you to watch DVDs and tapes on your vintage TV without such interference.)

If I'm receiving satellite TV via my home transmitter, I know that I'm working with a relatively pure signal and won't have to waste time chasing false symptoms caused by a new device.

This radio construction project, including all descriptions, diagrams, photos, and the underlying electronic design, is published here for the noncommercial use of radio hobbyists. You may print and reproduce these project instructions for your personal use. Commercial use of this material is strictly forbidden.