Why can't we make a balun?

[Nuttyprof 0]

I have taken it on myself to try and figure out the specs for the transformer inside a passive balun - I have heard it said here many times before that the parts are only a few bucks and after looking inside them I would agree. See below...

 

That being said does anyone have the expertise to help me spec what I think is termed an impedance matching transformer - cat5 / coax (75 to 100 ohms) - or better yet have a "Mouser" or the like part number? I'll be glad to share the solution with everyone if I succeed. So far all I know is the turns ratio of 1 : 1.3

 

----------- Previously posted -------------

The thing about baluns is that, despite the claims by some manufacturers, there really isn't much difference in the design or the costs of the parts. Basically, a balun is probably $2 to $3 worth of parts. See the schematic and diagram below:

 

A couple of connectors, a circuit board, a small transformer and a plastic case don't add up to much.

[rory 0]

Thats for the really basic passive baluns though, for something decent it is going to cost much more.

 

However, if you can come up with a cheap alternative to something like the active NVT gear .. im sure many here would buy them

 

BTW, FM-Systems manufactures alot of parts like that, might want to check them out also.

[Nuttyprof 0]

Thanks for the info... I'll continue to research it. If anyone has any other info let me know...

[perdueeye 0]

The big magnetic flux of the magnet in the coil is very important.

[survtech 0]

Thats for the really basic passive baluns though, for something decent it is going to cost much more.

 

However, if you can come up with a cheap alternative to something like the active NVT gear .. im sure many here would buy them

 

BTW, FM-Systems manufactures alot of parts like that, might want to check them out also.

Cost more - yes. Contain more expensive parts - no. They are all pretty much constructed the same.

[Doug 0]

I did a not very scientific test on baluns several months ago. I connected a camera up to 350 feet of cat 5. I used a FM systems cam master to measure the loss on sync & colour burst using various balun sets.

I used NVT, Muxlab, Nitec and two no-name baluns.

 

One of the no names performed the best in this basic test, keep in mind that a real world test may be different.

 

I used cat 5 on most of my installations and I've used hundreds of baluns, from various manufacturers including cheap $5 no-namers and I really haven't seen much if any difference between them.

[survtech 0]

My sentiments, exactly!

[rory 0]

Cost more - yes. Contain more expensive parts - no. They are all pretty much constructed the same.

 

Im talking about multiport transmitter/receiver hubs amplified with ground loop isolation and interference rejection, not just the cheap baluns on each side.

[perdueeye 0]

There is no uniform criterion in test of baluns. To majority, test is simple and just check the pictures by eyes. But that is enough. If you test them strictly, the test will cost a lot, but the differences are not very obvious.

 

Some baluns made in China are qualified and competitive in prices. Infact, a lot of named or unnamed baluns are from China, the "world factory".

[survtech 0]

Cost more - yes. Contain more expensive parts - no. They are all pretty much constructed the same.

 

Im talking about multiport transmitter/receiver hubs amplified with ground loop isolation and interference rejection, not just the cheap baluns on each side.

 

Maybe so, but his original post said:

I have taken it on myself to try and figure out the specs for the transformer inside a passive balun

 

And you said:

Thats for the really basic passive baluns though, for something decent it is going to cost much more.

No mention of active there.

 

For balun design here are some links. The bottom one is the most common design:

 

http://www.odyseus.nildram.co.uk/RFMicrowave_Circuits_Files/Balun%20Design.pdf

 

http://www.freepatentsonline.com/6917255.html

[EagleEye 0]

I actually just use a RCA with a screw on terminal with a a rca to bnc connector. it cost like 2.00 or so. and works for runs up to 150' using cat5e. I also use cat5e for the run up the wall from the dvr for the power and video and split it off to coax if needed or just more runs with a 2pair 22g wire. I've been in this business for 5 years and have done every installation my self solo. This seems to the best way for it.

 

Get the rca screw on terminal and rca to bnc at radio shack untill you find a dealer. I get mine free from my friend who owns a radio shack.

 

Albert

[survtech 0]

I actually just use a RCA with a screw on terminal with a a rca to bnc connector. it cost like 2.00 or so. and works for runs up to 150' using cat5e. I also use cat5e for the run up the wall from the dvr for the power and video and split it off to coax if needed or just more runs with a 2pair 22g wire. I've been in this business for 5 years and have done every installation my self solo. This seems to the best way for it.

 

Get the rca screw on terminal and rca to bnc at radio shack untill you find a dealer. I get mine free from my friend who owns a radio shack.

 

Albert

And you could dry your hair by sticking your head in your car's exhaust pipe...

 

Seriously, by attaching the twisted-pair directly to an RCA connector you are losing a major advantage of balanced cable - the ability to cancel out noise picked up by the cable.

 

A main feature of balanced twisted-pair video transmission is that noise is picked up equally by both wires in the pair. Since the signal on the wires is added out of phase at the receiving end, this cancels the noise (+noise + -noise = 0 noise). Your method would actually double the amount of noise in the signal.

[EagleEye 0]

I've never had any problems with that method. Color looks the same as it does on my longer runs. also i place all my wiring inside of steel conduit, as most of my installs are in factories and businesses.

[survtech 0]

I've never had any problems with that method. Color looks the same as it does on my longer runs. also i place all my wiring inside of steel conduit, as most of my installs are in factories and businesses.

So you go to the expense of running steel conduit, then cheap out on the transmission method? Besides, if you are running more than one camera signal within the same conduit you still have bleed from one camera getting into the other. The result would still be called noise.