C128 RF Output

[airship]

While contemplating what might be done to pimp out the various capabilities of my C128 (see ULTIMATE C128 post below), the only port I couldn't come up with something for was the RF port. Who uses RF, anyway?

So I took a look at the schematic:



and this question reared its head: "Does the RF box (which is a 'black box' on the schematic) boost the video signals before sending them to the 8-pin video connector, or does it actually sap some of their strength?" In other words, would we be getting a better video signal if we just ripped out the RF box and jumpered the video signal right around it? Who knows, we might even get rid of those pesky vertical lines.

Anybody have an answer?

Edit: I just noticed that the RF box is also where the composite signal is mixed, but I don't care about that, either.

[RobertB]

...the only port I couldn't come up with something for was the RF port.

Can the RF modulator be redone as a low-powered RF transmitter?

             Truly,
             Robert Bernardo
             Fresno Commodore User Group
             http://videocam.net.au/fcug

[airship]

Actually, it already IS a low-powered RF transmitter. So low-powered that it has to be directly connected to a TV's antenna terminals in order to be detected.

If you'd plug a long antenna wire of the correct length into the RCA jack on the back of the C128, you might be able to broadcast, what?, two feet or so?

If my research is correct, you'd need a diplole (C128 output connected in the middle of the antenna wire) length of 92 inches for TV channel 3 output.

I don't know if a TV distribution amplifier like this one would give you enough boost to let you hook up an antenna and broadcast. Maybe:



But there's no reason I know that you couldn't add an RF amplifier of the right frequency to it and get a broader range. The ideal thing, though, would be to get a UHF TV license from the FCC (here in the USA) and broadcast your C128 signal to a city-wide area.

[Wild Turkey]

"Who knows, we might even get rid of those pesky vertical lines."
Are the vertical lines 'inline' with the character set layout in 40 column mode?
I have read somewhere that this symptoms is inherant to the VIC chip version/era.

Thought of using a video sender internal to your C128 to get a transmitted signal on the UHF band? 

[RobertB]

Thought of using a video sender internal to your C128 to get a transmitted signal on the UHF band? 

Hmm, internal... well, if it won't fit a flat C128, it could fit into a C128DCR.  :-)

            Plenty of room in there,
            Robert Bernardo
            Fresno Commodore User Group
            http://videocam.net.au/fcug
            The Other Group of Amigoids
            http://www.calweb.com/~rabel1/

[hydrophilic]

I had the same broadcasting idea, Airship.  My tentative plan is to begin broadcasting in February 2009.  I'll need an interface to my PC to generate dynamic content.  And a good arial for broadcast.  I have an arial but it's quite beat-up due to neglect (hasn't been used in over a decade I guess).  In the tune-up process, I could cut out all the bars except 2 and cut their length to be a multiple of the broadcast wavelength.  I also have an RF amp similar to the one pictured, but it's for boosting incoming signals from the antenna.  I'm hoping it will work in reverse for broadcast   Based on elevation, I imagine it could go a few miles, but based on power I'd be suprised if it covers 1/2 mile.  Completely impractical but something to play with.

I'm too lazy to look it up, but I saw a web page where somebody did a similar thing (without outdoor antenna) to broadcast from an '80s machine the signal to a TV in another room.  I don't remember is it was a VCR or an ATARI 2600 or what... but hopefully you get the idea.

[airship]

I also have an RF amp similar to the one pictured, but it's for boosting incoming signals from the antenna.

That's exactly what the one pictured is for. I don't have one, unfortunately. But I thought it might be interesting to just hook a dipole directly to the C128 RF output jack and see if I can broadcast to a TV a couple of feet away. Hey, wireless monitor! Let's see your PC do THAT!

[hydrophilic]

Using a standard, shielded RF cable, I can broadcast a few inches!  I imagine with a normal wire (not shielded but with normal plastic insulation) you could broadcast a few feet without an amp.  Maybe several feet if you cut the wire to the right length and kept it parralell to the TV's antenna.  Oh yeah, an antenna on the TV will obviously help too   So rare nowadays...  Now that we're talking about it, I kinda of miss the old rabit ears!  ...but not the bad picture and adjustment needed whenever you changed the channel.

I remember when we had to GET UP and WALK to change the channel

[airship]

I remember when we had to GET UP and WALK to change the channel

Man, you're older than I thought!

We used to have a TV where we had to put a big rubber band on the tuner knob to keep tension on it so it would work.

Glad to hear you're a C128 broadcaster now! I agree with you; I think with a properly cut dipole on the C128 and a good set of rabbit ears on top of the TV, you should be able to broadcast without an amp to a TV across the room. Wireless monitor, indeed!