Any DIY balun info for S-video to Cat5 conversion?

So, video (including Y/C) is 75-ohms unbalanced, and CAT-5 is 110-ohms balanced. Baseband and Y/C Standard Definition television video needs a bandwidth of ~5MHz (As contrasted with computer or HD video which is significantly higher bandwidth.).

Given those specs shouldn't it be relatively easy to find a ferrite core (balun?, toroid?) that would do the job.

I would also like to identify a source of the appropriate core to make some video/Cat5 baluns. But I am unsure of how to interperet all the different ferrite types, shapes, etc. Assuming we can find info online somewhere to help calculate winding specifications? What about the LF response (50-60Hz)?

Or, just do what the commercial units do that you looked at. Coax (S-video) in to a video amp, out to a balanced CAT5. Then, on the other end, you have the same amp, just with the balanced in, and the coax out. Good chips will have equalization available to compensate for some of the high frequency losses.

Who makes good chips for this? Analog Devices, for one, IIRC...

Charlie

Hello Dave,

LAN transformers? I doubt you will achieve an acceptable image quality. Check this out:

Regards, Joerg

I read in sci.electronics.design that Dave wrote (in ) about 'Any DIY balun info for S-video to Cat5 conversion?', on Thu, 1 Sep 2005:

Try it with a 125 m 'throw-out' cable. If you can't get NE592 any more to give you a balanced output, there are plenty of fast dual op-amps that will. And the standard video input these days is a differential input with one leg grounded, and your balanced signal will be quite happy with that.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
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Hello Charlie,

Or ye olde uA733. Dirt cheap.

Regards, Joerg

I read in sci.electronics.design that Richard Crowley wrote (in ) about 'Any DIY balun info for S-video to Cat5 conversion?', on Thu, 1 Sep 2005:

Balun transformers have their advantages, but you can try a transformers solution as I explained and if it's OK, THEN tackle the balun question. Yes, video baluns are tricky, because you MUST lose the DC component.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Dave, you are making it unnecessarily difficult. I don't know about your budget and what part of the globe you're at, but $70 normally would not even cover any labor costs associated with installing 125' of CAT5E cable (depending on the environment, of course). On top of that you have your time to develop a balun (design, find parts, build two of them). You may very well be doing yourself a huge favor by spending only $70 on a pair of factory-made quality checked devices that will also likely withstand much more abuse than a bench-assembled prototype you'd build.

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Yep, at least a week on the workbench + test equipment, thats just to do a basic test. then PCB design, stripboard is not to good at video frequencies.

Check out Kramer, bottom feeders of the food chain, in this sort of market.

Might be woth just hiring the kit

or even running coax!

martin

"Dave"

** $70 is cheap.

The quality will not be perfect and EMI may still get in.

** No, video is not data !!

It is more like hi-fi audio that goes out to circa 5 MHz.

** Why not just use two runs of 75 ohm RG59 ?

The signal loss at 5 MHz over 125 feet is tiny.

.......... Phil

I'd rather not spend $70 US dollars (So. Calif location) for a passive converter only to find out that it works like crap. I'd rather not run RG6 which I'm sure will work when I can run Cat5E cable, use it for S-video transmission, OR ethernet, OR telephone, OR audio. There's a lot of benefit to running the cat5E.

I'm doing the installation myself through a 3" conduit that is run under the concrete slab from a soundboard 80' from a stage. So the installation costs are nil. Certainly plenum rated CAT5E is cheaper if I plan on running it through the ceiling.

I'm usually doing embedded controller stuff and spend my free time programming, laying out PCB's, stuffing, soldering and testing mostly for my own needs. Active electronics are not new to me, but RF stuff is.

Ye have so little faith in my construction skills!

I asked for a website or information on how to do this hoping that someone has already done this, figured out what cores to buy, turns of wire, etc to create something that works or claims to work. If it happens that the passive method is acceptable, I can see many other uses for this - running video from remote security cameras, in house S-video distribution along with sound, etc. For my needs beyond this particular project, I really don't want to spend $70 for each run to accomplish the conversion.

This is S.E.D. right? Note also that the $70/pair units I doubt are high quality - specs seems to be a bit absent on these passive units.

Thanks to all that answered. I'll take the active approach to get this immediate need done but do plan on seeing if I can go for the non-powered passive way 'in my spare time'.

Dave

Why not run both? At some time you may need the video and the ethernet connection. It will be cheaper to do it now, than have to replace it in the future. While you are at it, you can pull a cat 3 or a second cat 5 for future use, too.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

If $70 is too much, then just try running the signal over standard cat3 phone wire. You can also use a 470pf capacitor to convert the s-video to composite and back if needed.

On Sat, 03 Sep 2005 09:56:17 +1000, in sci.electronics.design Tony wrote: snip

and "cost" is part of the design process.

martin

All true; but this IS "sci.electronics.design", not "sci.electronics.buy", so it's a valid question.

And, having purchased bottom-end "video" baluns, I can attest to the utterly poor performance of at least the ones I tried (which, amongst other things, had very poor LF response, and tended to wash out the RHS of the screen, even with premium DC restoration performance in the receiving equipment).

Many have suggested active buffers in the past for this function, with good reason - it is hard to design passively-terminated magnetics to cover so many decades of bandwidth.

Tony (remove the "_" to reply by email)

"Dave"

** What you were naively hoping is just plain dumb. A high performance video balun is no simple device - even for an experienced transformer maker to produce.

The fact that you imagined a ferrite core with a few turns would do the job shows just how out of touch you are.

** Fine - just go to a store that sells such baluns and steal them. ** High quality ones came at a price that would realy scare you. ** Why not just *try* the cat5E as is - no baluns.

If the cable is in conduit under concrete that will provide reasonable shielding.

Results might surprise you.

............. Phil

Learning can be part of the design process too, weigh the value of the learning against the costs.

There is lots of balun design info out there, and here on my drive I find an old Signal Integrity list message from Ray Anderson on the subject, with book references which are likely to be more useful than SED for this particular design.

(BTW Ray Anderson is the administrator of the Signal Integrity list and a very well respected engineer, and no one chimed in with any additions or corrections.)

-------------------

Designing 1:1 Baluns for Receivers Date: Fri, 28 Oct 1994 09:38:32 +0800 From: snipped-for-privacy@EBay.Sun.COM (Ray Anderson) Message-Id: < snipped-for-privacy@uranium.EBay.Sun.COM> To: snipped-for-privacy@netcom.com Subject: designing 1:1 baluns for receivers

Dave W6MIK recently asked me a question about designing small baluns for use in a receiving converter between 40 and 70 MHz.

I've put together some notes on this and thought there might be interest amongst the other homebreweres on the list about this topic.

I'm certainly no expert on this topic, what I've put down comes from several of the common references on the subject. If there are any errors they are probably my own and I retain copyright to them :) If anyone on the list knows more about this than I do, ( and I sure hope someone does) feel free to make corrections and comments.

72's de Ray WB6TPU snipped-for-privacy@uranium.ebay.sun.com

-------------------------------------------------------------------------- Here is a bit of information on building small baluns using toroids or 2-hole cores:

. out <--------------------mmmmm----------+-- GND | +----------------------------+ (balanced) | . +-------------mmmmm----------+ | out <-----+----------------------------+ | . +-------------mmmmm------------< <= Unbalanced Input

(dot on end of inductor indicates phasing)

1. The device is wound with trifilar wire. (use 3 different colors if you can to help eliminate confusion)

1. First, determine impedance (Zo) the balun will be used with. Zo=sqrt(Zin * Zout)

2. Rule of thumbs says the inductive reactance Xl of each winding should be 4 to 5 times Zo. (So for 75 ohms in/out Xl=300 ohms to 375 ohms)

1. Determine the inductance for the Xl at the lowest frequency you want to use the device at. (for Xl=300 @ 40 MHz L=Xl/(2*PI*F)= 1.2 microHenries)

2. Select the core material: for HF to low VHF Amidon type 63 or 61 Ferrite material would be appropriate. These have mu values of 40 and 125 respectively. At lower frequencies you would want to use something with a mu of several hundred. At higher frequencies a mu of 5 - 10 using powdered iron material might be appropriate.

1. Select the core size: FT23 is .23 inch diameter which is one of the smallest sizes commonly available. Bigger parts can handle more power before saturating as a rule. Choose the size that fits your application.

2. Look up Al value for the core material/size in a catalog/databook. core FT23-63 Al=7.9

1. Calculate the number of turns required. N=sqrt(L/Al)*1000 (L is in mH) So N=sqrt(.0012/7.9)*1000 = 12.3 turns

2. Wind 12 turns trifilar according to diagram above.

The same logic works if you are going to use double hole "binocular" balun cores. The number Al will be different but is obtained from the core manufacturers literature.

With small cores you need to use small wire. #28 or #32 or even #40 might be appropriate for FT23 size core. The higher the mu value and the lower the frequency, the more turns you are going to need.

There are other topologies for 1:1 baluns, but all the calculations are still the same, just different number of windings and connections.

We haven't considered power levels or core saturation since we have assumed we are making the balun for a low power receiver application. For higher power applications there are additional things that need to be considered or else the core will saturate with magnetic flux, and the coupling between windings will decrease and the thing won't work correctly (and may go up in flames).

See Sevicks books on Transmission line transformers, The ARRL Solid-State Design Book, and Haywards book on RF design for other good info on designing these type baluns. The Amidon catalog and Ferroxcube catalog amongst others also have some good info as well as the Al values for their particular cores.

Ray WB6TPU

He does not mention DeMaw's book which covers all things high frequency ferrite...

Author: Doug DeMaw Title: Ferromagnetic Core Design & Application Handbook Publisher: Prentice-Hall Year: 1981 Cost: (out of print) ISBN #: 0-13-314088-1 Pages: 256 Contents: Fundamental information on core and inductors using ferrites and powdered iron mixes; rumors of reprint possibilities.

Uh ! ?

I'm not sure whether to laugh or cry.

Graham

An *RF* balun like you posted is going to be ZERO USE for a *VIDEO* signal !

Video goes down to 50Hz.

Graham