BNC to RJ45 Converter

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ashleysmithd
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BNC to RJ45 Converter

Post by ashleysmithd »

Hi,

I wanted a bit of advice on building some BNC to RJ45 converters. We have an issue in a broadcast event I am engineering for where we do not have sufficient access to wallboxes (due to an installation screwup) so we're thinking about using the CAT6a tielines to send video & embedded audio over.

Due to the inner core of RG59 cable being larger than a single Cat6a core I understand the impedance will probably be mismatched, and there is less shielding so we won't be able to send HD-SDI very far over it. My plan was to use all 8 cores, 4 live 4 return. Does this sound feasible? I realise there are converter boxes out there that do this but this is a student run event and we can't spend chunks of our budget on converter boxes. We have a huge network infrastructure however and if we could use this to send video and audio over it would really save us.

Any advice appreciated.
Thanks.
Student Broadcast Engineer (Just started, so please go easy :P)

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PID_Stop
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Re: BNC to RJ45 Converter

Post by PID_Stop »

Generally, BNC to RJ45 adapters are baluns -- that is, a transformer that matches a 75 ohm unbalanced coaxial feed to a 100 ohm balanced twisted pair. The highest speed baluns I have seen for video are 270Mbps, which is standard definition. Unfortunately, this is a rather inefficient approach: a typical SDI balun like the ETS PV850 limits the maximum distance to about 135 meters even with very good twisted pair cable; by contrast, you can go twice that distance with Belden 1855A coaxial cable, and that isn't even the best coax available.

HD-SDI would require that your twisted pair cable and baluns work at 1,485Mbps. I doubt that even Cat6E cable would support that rate for any significant distance, and have never seen a balun designed to run at that rate.

Belden 1855A is slightly smaller than four-pair network cable... is it possible to use several of the existing cables to pull 1855A through to where you need it?

-- Jeff

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ashleysmithd
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Re: BNC to RJ45 Converter

Post by ashleysmithd »

Unfortunately the IT department in our college are very conservative about the facilities and we're surprised they agreed to us using and re-patching their existing network for this, but I will ask and see what can be done. My other (untested) option is to take firewire outs from the camera(s), connect them to a laptop and stream the 25Mbps HDV through the network. No where near HD-SDI standard but, at least it may be doable and it's still HD.

Will look into streaming options.

Thanks.
Student Broadcast Engineer (Just started, so please go easy :P)

eadler
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Re: BNC to RJ45 Converter

Post by eadler »

Can you switch it at the event and just send a switched feed back?

When I was a student TV station's student engineer, our school built a brand new arena (hockey is big there). We ran the first year and a half to an old switcher and mixer in the corner of the arena and sent the mixes back to the studio, over a single fibre run (SD analog), where the graphics and replay were handled. This stopped due to the station being moved and triax patching to the arena being put in -- now, due to a lack of ties and lack of switcher inputs, they switch an in-game show from a 20RU cart in the arena (the in-game show takes place where our makeshift control room was) and switch that in with the game cameras back in the control room.

Does your facility have glass that they can patch rather than twisted pair? If so, you can look into acquiring fibre converters. They're relatively expensive compared to simple baluns, but they work reliably.

Get creative!

Also, remember, usually the content is much more important than image quality (although the best quality you can reasonably pull off should likely be used)
Eric "tonsofpcs" Adler
http://www.videoproductionsupport.com/
Twitter: @eric_adler

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PID_Stop
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Re: BNC to RJ45 Converter

Post by PID_Stop »

eadler wrote:Also, remember, usually the content is much more important than image quality (although the best quality you can reasonably pull off should likely be used)
This is a good point. Have you considered transmitting anamorphic SD -- that is, taking the 16:9 HD and downconverting it to squeezed 4:3 SD, transmitting that over your twisted pair, then upconverting and stretching it back out to 16:9 on the far end? That would bring the data rate down to what a balun could handle, at least for a hundred meters or so.

We have a local station that is doing the anamorphic SD trick for their local news and calling it "enhanced widescreen"... and it's amazing how many people assume that it's HD just because it fills the whole 16:9 screen. (Pay no attention to those ragged edges... :wink: )

-- Jeff

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Re: BNC to RJ45 Converter

Post by TheSigma »

ashleysmithd wrote:Due to the inner core of RG59 cable being larger than a single Cat6a core I understand the impedance will probably be mismatched, and there is less shielding so we won't be able to send HD-SDI very far over it. My plan was to use all 8 cores, 4 live 4 return. Does this sound feasible? I realise there are converter boxes out there that do this but this is a student run event and we can't spend chunks of our budget on converter boxes.
I think you get the Idea, but what you are describing is not feasible. for one, most category cable has NO shielding, it is meant to send balanced signals and therefore does not require it(Some is shielded, but the vast majority of stuff I have encounered is not). and if by 8 cores you mean the 8 individual wires inside the outer jacket,well no can't do that either. even a composite video Balun requires a pair per channel(A Balanced signal is always on a pair of wires), so you could easily do 4 composite video signals with an appropriate balun. An SD-SDI Balun is going to be about 80 bucks, you need one on each end of the cable, and if you really need4 send and 4 return you will need two category cables, and 16 baluns, $1280 (actualy if you order 16 you should get a price break). now if you send a switched feed and need no return your at $160, $320 for one return. that will be SD though. HD only option is fiber, looks like 1600 a pair on those converters.......

Perhaps this will put things into perspective. not sure if 160-320 dollars is a "Chunk" in your budget or not. In the world of broadcast gear though, thats Chump Change.....Heck even the $1280 is cheap by some standards.

Hope you can work something out.

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ashleysmithd
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Re: BNC to RJ45 Converter

Post by ashleysmithd »

Ok thanks for the advice.

The issue we're having is that the wall boxes have been installed within risers, which are temperature controlled and any access is considered a fire door, so we can't leave anything open. The construction of the building means each of the levels overlap one another, so if we were to run coax cables down levels we would need excessive lengths and things would probably get pushed over the digital cliff. Not to mention it won't look nearly as nice having dozens of cables running down levels. Fiber is possibly an option, not something we have in hand right now though.

So, on floors where we do not have wall boxes outside of the risers, the only real tie lines back to CAR are the cat6a sockets. And of course, the network cabling is installed within the trunking into the rooms so it would mean we can avoid running anything through doors. Unless we started embedding the longer cable runs into the wall trunking, which is a possibility.

The project is still in early stages and I want to try and offer advice to the operational team as to what is more feasible, and hoping they will take the advice and use up any rooms with accessible wall boxes before asking to use rooms where we only have cat6a.

I've searched and found the SDI balun, if it comes to something like a switchable mixer output for preview then it sounds like a reasonable plan. My worry is if they ask to have 4 cameras inside a room all with HD-SDI outs which need to be patched into CAR somehow. With a few returns of course. We really would like to make this entire event HD if possible.
Student Broadcast Engineer (Just started, so please go easy :P)

eadler
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Re: BNC to RJ45 Converter

Post by eadler »

If they're willing to pull it through walls, maybe even buy a spool of cable, crimp tool, and connectors, and put BNC 'keystone' barrel jacks in the wall plate with the existing RJ45s (sure, it isn't as great as a direct terminated female BNC on the cable, but it should give you a usable signal)...
Depending on your run lengths, this may be feasible. Run all the coax into a telecom patch closet, put a line of BNC barrels there as a patch panel (or get a true patch panel) and have another set of runs that goes to your production control, maybe even add some runs to other places, patch as needed. You may have 4 cameras and 4 inputs, but you can build this for even more camera positions (with the coax terminated as close as possible to desired camera positions) and simply patch the positions that you want to use for each event held in that space -- you can even patch returns to various points, useful for in-event-space monitors that you drive from a different bus of your switcher (rotating graphics, zoom-ins of speakers, instant replays, etc.) amongst other things. As for returns to the cameras, I wouldn't worry about them unless absolutely necessary. One piece of coax per camera should be plenty. Train your camera operators to act as if they are always live and to pay attention to communications from their director. You may be able to build simple adapters to the UTP (cat5/6) cable runs for communications systems, if needed.

In the aforementioned "new arena", due to cable run issues, we had a few camera locations that had these keystone BNCs for video (we did mostly analog, but some SDI and HDSDI would have been doable) and hand-soldered manually-built-into-keystone-caps 3.5mm stereo females for audio send (single channel per position) and intercom (Clearcom/RTS system). Each of these panels also had two RJ45s in it which we did not use.
Eric "tonsofpcs" Adler
http://www.videoproductionsupport.com/
Twitter: @eric_adler

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ashleysmithd
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Re: BNC to RJ45 Converter

Post by ashleysmithd »

I think the realistic approach with this is to run a loom connected to a CTP from the room(s) which would then connect to a flyaway where any program making will take place and then a single program output with embedded audio will be sent down a mini-loom back to CAR. That way nothing exceeds our 90m guideline digital cliff and only a select few cables are being run up or down levels. It's finding out the capacity and gaining permission to run looms through IT's trunking that's the issue.

Hopefully this will only need to be done select amount of times. We have wall boxes in other rooms which run directly to CAR, but this event is pretty large and we need to accommodate for a lot of areas.
Student Broadcast Engineer (Just started, so please go easy :P)

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