atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Coax, a stupid question (length limit):

Is there a length limit for Coax?

I'm trying to upgrade a video security system, using cables already run by some unknown person at some unknown time. I also ran one Siamese cable to bypass a cable with an end that had been plastered over somewhere.

On the old siamese, I can see the entire cable run -- it goes through a garage, strapped to pipes along the way -- but I can't get any indication of continuity, and I can't get a video signal. It's about 200'. I thought it might be a bad cable -- maybe it got cut in the middle somewhere -- but the new Siamese that I just ran acts the same way.

I know that the cameras are compatible b/c I can connect them directly to the system and they work; I also successfully installed one on an existing cable in a stairwell, so I'm pretty sure that the cable is compatible with the connectors.

But the remote ones are kicking my butt.

I'm using compression-type RG-59 BNC connectors purchased at Home Depot.

Is it length? Is there any way to test or certify a BNC coax run? Any other suggestions or thoughts?

My next step is to run an RG6 (not Siamese) and use RG-6 Compression-type BNC connectors (I can find power locally for most of the cameras anyway). Any ideas would be deeply appreciated.

(1) Check for power:

On the new 200' run, do you get power on the power pair?

(2) Check for effect with 200' of wire:

If you take a 200' roll of siamese, sitting in the room with the server, and connect a camera, does it work?

(3) Check for continuity:

What are you using to check? Meter? Test lamp? Toner?

(4) Forget about Radio Shack:

Their stuff, by and large, is for civilians and DIY-ers.

I agree with Arthur. It is probably the power pair of the siamese and not the coax portion. I would try to test with a little TV at the camera to see if the power is getting to the cam from 200 feet away. Also, powering the cam locally is also a good idea. Plug in the power supply with an extension cord and see if you get signal locally, then see if you get signal at the head end, then you know you have a power issue, not coax.

Ditto. Even if the length was excessive, you would still get a picture. It would just look bad. It isn't often that a signal of any kind drops completely dead at a specific distance, it just degrades.

I'm plugging in the cameras locally, so the power pair of the siamese is bypassed. I can make the cameras work at the DVR, but extending them through the siamese is a no-go. I did get one existing siamese to work, so I know that the cameras will work with the cables and I'm not just consistently screwing up the terminations.

I've already run the cables, so I can't coil them up and test at the DVR, as Arthur suggested. Also, this is not Radio Shack cable.

I could check for continuity on the power pair, maybe.

I checked continuity using my tone generator on the continuity setting: I twisted the mesh around the center and then looked for continuity between the mesh and the center at the other end. I also put a tone on the cable (one clip on mesh, one on center), and was able to hear a very faint tone with my wand down to within twenty feet of the other end.

Sounds like cable length is not my issue. Is there a way to loop back and test other than wrapping the mesh around the center and looking for continuity at the other end?

Remove the shunt at the end where you made it (the braid and the center conductor twisted together) and test WITH AN OHMMETER again for continuity.

I think you have a short circuit in the coax.

if the cable is in good shape and the terminations are good you should be able to run up a 1000 feet no problem...
:read:

I'll give that a shot.

I certainly did not mean to imply that you actually would rip the walls apart and retrieve the exact coax that is giving you trouble. I wanted you to consider taking a DIFFERENT piece of coax, of the same or approximate length, and do a test using that length of coax, to duplicate the physical run.

At the moment I'm out of siamese. I did make a 100' loop of RG-6, term with RG-6 BNC fittings, and got a good test. I was also able to use a 60' cable that came with the system and got a good test.

I tested the siamese runs, center conductor to braid no-shunt (as someone suggested) and got no continuity. I will test again with an ohm meter.