VGA to RF coax

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15-05-2008, 02:20 PM
Peter

VGA to RF coax

Hi guys,

For an upcoming project we need VGA to RF coax. Catalyst will control 20 old tv's with the same image, which will all possibly (we're still searching them) only have the RF coax input (antenna).

So i suppose when we would first need to get from VGA to something like composite (bnc or rca), then to a splitter and then convert to RF (cable runs from 10-75m). But where can we find such devices?

If this wont work we will try to build in tft's in the old tv cases. Budget allowing.

Thanks,

Peter
15-05-2008, 02:42 PM
Marty Postma

You should be able to find a VGA to Composite scan converter in any basic electronics shop (tell them you need to display a computer monitor on a TV)....then a basic VDA (Video Distribution Amplier)--or several hooked up together--for composite video.

***EDIT*** You may only be able to find composite gear with RCA jacks in which case you whould then get RCA to RF adapters....should be fairly inexpensive all in all***

Check the connections onthe back of the TVs b/c you might be able to daisy chain a few of them if they have RF out jacks.

Hope this helps:)
15-05-2008, 03:17 PM
SourceChild

Got mine at radio shack. It was cheap (under $20 USD). Has RCA for stereo L&R and composite for inputs and a regular RG6 RF plug on the output.

Oh and the RF distribution amp was less that $100 USD. Also from radio shack. The ones I use have 8 or so outputs each

It's funk though. Don't adjust the aspect ratio on your output. Your video monitor will be wide but it will look right on the TVs.

I've done this a zillion times in nightclubs.
20-05-2008, 06:36 AM
Peter

How long can i go with coax 75 ohm cable (RF)? And does it pick up interference from powercables, speakercables, dmx?

We will be working on a location so it's important.
20-05-2008, 05:09 PM
Marty Postma

Quote:

Originally Posted by Peter

How long can i go with coax 75 ohm cable (RF)? And does it pick up interference from powercables, speakercables, dmx?

I personally would try not go more than about 100'-150' or so with RF even though longer runs should be possible.

If you are laying them along the same path for long runs you will get interference from power cables, so defintely keep some humbuckers on hand.

DMX shouldn't really bother it as long as they are properfly shielded DMX cables.

Hope this helps:)
21-05-2008, 10:28 AM
emilianomorgia

Quote:

Originally Posted by Peter

So i suppose when we would first need to get from VGA to something like composite (bnc or rca),

Overview
The Apple DVI to Video Adapter was designed to allow Mac Pro (with ATI X1900 XT), MacBook Pro, Mac mini and Power Mac G5 users to connect the DVI port to an S-video or Composite video device such as TVs, VCRs or overhead projectors with S-Video or RCA (Composite) connectors. The Apple DVI to Video Adapter is designed to work with the DVI port on the Mac Pro (with ATI X1900 XT) MacBook Pro, Mac mini and Power Mac G5 systems only.

Use a separate DVI to VGA Adapter for VGA video out for Mac Pro, MacBook Pro, Mac mini or Power Mac G5 (included with all Mac Pro, MacBook Pro, Mac mini or Power Mac G5 systems or available for order as a standalone kit).

Important:
Requires Mac Pro (with ATI X1900 XT), MacBook Pro, Mac mini or Power Mac G5 with DVI port.

http://store.apple.com/1-800-MY-APPL...&nplm=M9267G/A
03-06-2008, 12:15 PM
Peter

Quote:

Originally Posted by emilianomorgia

[COLOR="DimGray"]Overview
The Apple DVI to Video Adapter

Is it possible to use this adaptor (second output) together with dvi-vga on the first output for monitoring purpuses during rehearsal (reprogramming)?

Wouldnt i be better of with composite?

Can i mix RF tv's with composit tv's without seeing the difference in image quality?

Thanks again!
03-06-2008, 05:05 PM
Marty Postma

Quote:

Originally Posted by Peter

Can i mix RF tv's with composit tv's without seeing the difference in image quality?

RF is really just a different plug for the same signal type as RCA composite...you won't see a difference between the two, but in my experience RF cables do seem to be more prone to signal interference from power lines etc.
03-06-2008, 08:35 PM
emilianomorgia

Quote:

Originally Posted by Peter

Is it possible to use this adaptor (second output) together with dvi-vga on the first output for monitoring purpuses during rehearsal (reprogramming)?

Wouldnt i be better of with composite?

Can i mix RF tv's with composit tv's without seeing the difference in image quality?

Thanks again!

i'm on a show rightnow . Mac pro 3 Giga xt1900
first output 1024x768
second apple video adaptor ....

The good news is I've switch from a FOLSON converter ( 3000 euro ) to the video adaptor ( 19 euro ) with no different on the final result
04-06-2008, 08:40 AM
SourceChild

Quote:

Originally Posted by Marty Postma

RF is really just a different plug for the same signal type as RCA composite...you won't see a difference between the two, but in my experience RF cables do seem to be more prone to signal interference from power lines etc.

Marty,

You are correct that both are RF signals. However, a "cable" signal traveling down RG Coax is very different from Composite Video.

The impedance is different between the Coax used in RG cable and the coax used as a shield in RCA or BNC type composite.

The "Radio Shack" type RCA cable is low quality with a lower resistance. The wires are stranded and very much more catering to voltage transmission than to RF transmission. (Basically crap but okay in small runs)

75 Ohm Video cable with BNC termination is specifically designed to transport the "video range" spectrum of RF signals. The tolerance of it is exceedingly higher than anything else. It also has much tighter twisted center wire, or solid copper.

Regular old RG6 type coax cable is solid core copper which means it is much better as a transmission medium for the modulating frequencies of VHF and UHF. In fact, it was designed specifically to transmit the ranges known as VHF. The shield diameter is larger that High quality 75 Ohm cable. The larger dia allows the sub harmonics to pass through the shield to eliminate ghosting sub harmonic reflections. Whereas in pro video cable, the shield is much tighter to enhance the filtering of electric fields and magnetic transients.

Another thing to mention is the nature of the difference between VHF and CVBS. Composite called CVBS (or Color, Video, Burst, Sync composition) is an RF signal where the scan rates are frequency and amplitude based. VHF however performs a frequency modulation of CVBS so that it can be encoded to a specific frequency channel for amplification and transmission.

Another way to think of it is that you need a tuner to use RF. RF has audio multiplexed with it.
04-06-2008, 08:43 AM
SourceChild

I like Emiliano's idea.

Just make absolutely sure to put an isolated signal amp between the cable run and the adapter because the slightest little spike or any noise will fry your video card.
04-06-2008, 11:09 AM
Peter

Quote:

Originally Posted by SourceChild

I like Emiliano's idea.

Just make absolutely sure to put an isolated signal amp between the cable run and the adapter because the slightest little spike or any noise will fry your video card.

So something like the kramer vm-25, http://kramerelectronics.com/indexes...sp?name=VM-25?
04-06-2008, 02:03 PM
SourceChild

Quote:

Originally Posted by Peter

So something like the kramer vm-25, http://kramerelectronics.com/indexes...sp?name=VM-25?

Good choice. The 1021 is also fine. The point is to have a filtering device in the path. Even if you had a single TV you were driving. It's always good practice to use some sort of "gatekeeper."

Similar to the way you typically always have an opto-splitter at your stage rack for DMX.
05-06-2008, 08:08 PM
Peter

So i would also get away with a kramer pt102vn?
06-06-2008, 12:54 PM
Peter

Quote:

Originally Posted by SourceChild

Just make absolutely sure to put an isolated signal amp between the cable run and the adapter because the slightest little spike or any noise will fry your video card.

What's the reason for that? Because i dont understand, my next question would be : is it the same for VGA? Now i connect graphics to splitter/booster and then to the projector.
07-06-2008, 11:12 AM
Peter

Quote:

Originally Posted by Marty Postma

I personally would try not go more than about 100'-150' or so with RF even though longer runs should be possible.

And what about going 25m - booster - 25m?
18-06-2008, 10:12 PM
SourceChild

Quote:

Originally Posted by Peter

What's the reason for that? Because i dont understand, my next question would be : is it the same for VGA? Now i connect graphics to splitter/booster and then to the projector.

Chances are you'll be fine but when you plug a string of video devices together, you run the risk of noise and feedback. Some noise is okay but even if you don't visual see it, there could be damage done to your video cards as they are more delicate than other components in the chain. The isolated splitter is a good idea to protect your gear the same way you would use a surge protector.

it's not necessary though.