electrical question

[darkpaw]

OK, I've done a fair amount of electrical work in my day, but this one just has me stumped.

Why is it that I can run a 75-100' RCA cable and get a perfect picture, yet if I run 75' of Cat5e I get nada? I checked for shorts, and there is none...the cable is in perfect physically. Figuring it was some kind of a resistance problem due to the thinness of Cat5e (it's what, like 22-24 AWG?) I tried several variations of it...and all still come up with no video. Sending POWER over it is fine, and the drop in voltage is almost nil. But even with these combinations, I get no video signal over it:

Used only one TP (orange/stripe, to be exact) and got no signal.

Used one TP for the + of video and one TP for the GND of video (blue/stripe and green/stripe, to be specific), and got no signal.

Broke up two sets of the TP and used the solids for the + of video and the striped for GND of video, and got no signal.

What's the problem? I see that normally when using Cat5e that many people put it on the video modulator (the convenient way to connect the power and video cables into the single Cat5e cable), but unless this is doing some kind of signal amplification, there is no electrical reason to do this -- it might make the connections more durable, but for the purposes of only testing, it shouldn't matter.

I'm just experimenting with Cat5e now, to try to cut down on costs for long-distance cable running...but this is confusing me. I can't see any reason why this doesn't work.

Ideas and opinions welcome.

[gasmasher]

I can't answer the technical reason, but I believe it has to do with the shielding in coax.

You can use cat cable if you use the device you mentioned called a balun. I have not used this store but here is an example. They have single and multi-stream options. The Video Balun for CCTV (BNC-RJ45) isn't too expensive. Just remember that you need one at each end of the cat cable.

Edit:
I just noticed that Bluecherry also sells baluns. I can vouch for them since that is where I bought my most recent cams and capture card. Good folks.

[cordel]

You have to have a Balun when you use cat5, cat5 impedance is higher than a coax and it is not balanced which is why you need a balanced/unbalanced (balun) device to match the impedance for you at each end of the cable.

[curtishall]

We also have this available if you don't want to install balun's:

http://store.bluecherry.net/product_p/c ... _500ft.htm

You have to have a Balun when you use cat5, cat5 impedance is higher than a coax and it is not balanced which is why you need a balanced/unbalanced (balun) device to match the impedance for you at each end of the cable.

[darkpaw]

Well, an interesting turn of events in this one, for a follow-up...

Turns out the camera I was using for testing ended up being defective. I tried it with another camera, and it works fine. Without the baluns. Resistance in the cable is less than 5 ohms at 100' under no load, which is comparable to coax. The picture is crystal clear.

I notice that the range of the baluns are over 1200'. Perhaps at larger distances, the balancing would be required, but at 100', it isn't necessary.

Thanks for the replies. Hopefully this information will prove useful for others in testing and setups.

[jameswilson]

on short runs you will get away with it, but video needs a coax or a balun.
Agreed short runs are fine but you may get problems with zm as it looses sync. As video contains some fairly high freq, pure resistance isnt the measurement that matters, you could have less resistance on 1000m of cat 5 or you could use a thick mains cable, wouldnt work mind but would have a lower resistance.
If its for your own home etc then fine but i would never fit A system for a client this way.