VGA over Cat 6

[museav]

This thread seems to cross several topics! Ruinexplorer provided a nice link to the connectivity in a VGA connector and if you note, the relevant video signal information is red, green, blue, horizontal sync, vertical sync (or a composite sync instead of separate H and V) and the related grounds. This is where the common term RGBHV comes from, the actual video signal content in a typical VGA connection. Those are the signals that typically have to be transmitted.

You can transmit those signal using VGA cable, which if per standard practice uses mini coax for the red, green and blue signals and twisted pairs for the sync signals. However, the small gage cable used typically results in higher losses and thus limits the length possible without signal degradation. It is common in installed systems to use a RGBHV cable that uses five separate coax cables bundled in one overall jacket. This is available with a variety of coax sizes and quality and can allow for much loner runs.

The most common "VGA" over UTP solutions simply replace the coax with twisted pair cable, running both sync signals on one pair. The baluns or interfaces do not do much other than handle to physical connections, impedance matching, etc. necessary to transition from one physical type of wire to another. You are still sending an analog signal on the wire, just using a different wire.

A step up from that are active interfaces that incorporate signal processing such as gain, EQ and skew compensation. These may also process the signal such that a single 4 pair UTP cable can support mono or stereo audio and in some cases even serial control signals as well as RGBHV video signals. But it is still analog video (and possibly audio) being transmitted and still simply a matter of a different physical cable versus a different form of signal.

It is a completely different subject when you get into converting the analog VGA/RGBHV video signals into some other signal format for transmission, be it an Ethernet data stream or some proprietary format or whatever. Video over a network is very different than video over UTP.


Always be very careful when comparing video over UTP device specs! There are few, if any, standards and a lot of very questionable practice in defining the performance of these devices. When a product identifies an X foot range, how is that determined? What signal (resolution, refresh, etc.) does it represent? What determines the result being acceptable?

As far as video over UTP devices, I have also had very good luck and support from Extron and FSR. While I have had very good experiences in the past with Magenta Research, I was out on a project site yesterday where we experienced a high number of failures with some of the new Magenta products. I am hoping this is an anomaly and not a change in the quality I've come to expect.

I have yet to find a reasonably priced wireless transmission solution for higer res graphics that also worked well with motion images.

 

[gafftaper]

I assume you mean something like this? Just curious, what does this type of system set you back? How well does it handle being near other wireless communication devices (mics, cell phones, etc.)? I know most mics are below that frequency, but I think there might be some that do.

I see that one of their selling points is that it won't interferre with wireless routers, which is good.

The only downside, again, is that the resolution is NTSC, which is lower than FMEng wanted. Wireless video is definitely gaining ground, but not quite ready for all video applications.

Yeah that's the one. I think we paid around $350 for a kit with transmitter and receiver. We use it for our Infrared stage manager's monitor camera (Sony handicam in nightshot mode with a S4 par filtered to only produce IR). It's nice because I can move the camera anywhere in the theater and not worry about cable. On the other hand there's always a good deal of wiggling antennas on both ends to get the picture perfect... but again that may be more due to my theater's steel catwalks and steel studs in the walls. I would be curious to see how it does in a big proscenium house where it's got an open shot from front to back of house.

It doesn't seem to pick up cell phone interference but it does clearly matter how close the receiver is to the monitor and other electronic devices in the booth. I have it right against the window and as far away from other interference as possible. Once we get it tweaked it produces a suitable picture for our backstage tech needs... but it wouldn't be acceptable for something like a lobby feed.

 

[FMEng]

Based upon what I have read, everything Museav says is right on. Baluns can convert the signal to a different cable type, like UTP. Adapters can convert it to a group of bigger, individual coaxial cables.

A different cable type will help it go further because those cables will have less high frequency roll-off than the regular VGA cable. But, they too suffer from roll-off, it just takes a longer distance for it to take effect. That's where the extenders come into play. They have equalization and gain to overcome the normal roll-off properties that every cable has.

It's fairly easy to get NTSC to go long distances with good cable. But, higher resolution, like XGA, is tougher to do.

.
The most common "VGA" over UTP solutions simply replace the coax with twisted pair cable, running both sync signals on one pair. The baluns or interfaces do not do much other than handle to physical connections, impedance matching, etc. necessary to transition from one physical type of wire to another. You are still sending an analog signal on the wire, just using a different wire.

A step up from that are active interfaces that incorporate signal processing such as gain, EQ and skew compensation. These may also process the signal such that a single 4 pair UTP cable can support mono or stereo audio and in some cases even serial control signals as well as RGBHV video signals. But it is still analog video (and possibly audio) being transmitted and still simply a matter of a different physical cable versus a different form of signal.

It is a completely different subject when you get into converting the analog VGA/RGBHV video signals into some other signal format for transmission, be it an Ethernet data stream or some proprietary format or whatever. Video over a network is very different than video over UTP.


Always be very careful when comparing video over UTP device specs! There are few, if any, standards and a lot of very questionable practice in defining the performance of these devices. When a product identifies an X foot range, how is that determined? What signal (resolution, refresh, etc.) does it represent? What determines the result being acceptable?

As far as video over UTP devices, I have also had very good luck and support from Extron and FSR. While I have had very good experiences in the past with Magenta Research, I was out on a project site yesterday where we experienced a high number of failures with some of the new Magenta products. I am hoping this is an anomaly and not a change in the quality I've come to expect.

I have yet to find a reasonably priced wireless transmission solution for higer res graphics that also worked well with motion images.