Subscriber Discussion

Practical Limit For POE And Data Over Single-Pair Of UTP?

I have something weird to share: During the course of testing IP MP cameras without a suitable infrastructure, we were provided with Vigitron Vi2301/Vi2316 evaluation units to transport the stream from an IP MP camera approximately 600 feet. We were unable to get the camera to power up and found that the Vi2301 and Vi2316 devices will not provide POE over a single pair. We learned that both the Vi2301 and the camera needed to be powered at their locations. Since the camera we tested was POE only, we would have had to power the Vigitron with 24VAC or 12VDC and add a POE inserter for the camera. The really strange thing is that when presented with the problem, Vigitron provided two Vi2401's with coax-to-UTP converters (basically baluns with, I believe, the transformers bypassed). Essentially, the coax-to-UTP converters just changed the connector from a pair to a BNC. The biggest shock was that this Rube Goldberg setup actually works! We are getting reliable POE power for both the camera and the Vi2401, plus 100Mb/s data transport over an approximately 600 foot length of a single 24 gauge pair of Cat5. Total draw of the two devices (Vi2401 and Axis P3364) is supposedly 14.6W (12.1W for the P3364 and 2.5W for the Vi2401). This flies in the face of everything I learned about electronics in over 40 years. Any comments?

I haven't tried one, but Axis sells a T8129 POE extender for UTP. The coax solutions are typically for traditional analog CCTV to IP upgrades. Interesting to hear you intentionally ran COAX for the POE features.

Interesting solutions to connect ip camera <a href="SIGRAND | Home"></a>, can connect the chain of cameras from one PoE switch port, maximum distance up to 500 meters. For distance of several kilometers can be used SHDSL extender or cameras with built-in SHDSL modem.

Undisclosed, we didn't intentionally run coax for our tests - it is already there. But neither did we use coax for the test. This was over a single pair of UTP. Vigitron provided the Vi2401's with modified baluns (tranformer jumpered out?) to convert UTP to BNC at each end for our testing. So 600' of a single pair of 24 gauge wire is transporting 100Mbps plus POE to power both the camera and the Vi2401 transmitter.

The point is, we don't have an IP infrastructure. All analog with ~50% coax and ~50% single-pair UTP using baluns and some active receivers. Converting to all-IP would be too costly and using 4 pairs per camera would require running a boatload of plenum UTP; also costly. And difficult, considering how overloaded and difficult to access our cable trays are.

When I had power issues in the past - I measured 4 Ohms resistance through 180FT of 24AWG, so 1200FT (600FT round trip) would be about 24 Ohms resistance.

Now, want to deliver 15W to power the equipment, but assuming 80% PSU efficiency, we actually need to transmit 15/0.8 = 19W.

V = IR, where V is the voltage drop across our 1200FT cable), R=24, and I, the current, depends on the voltage used by Vi2401 to transmit between the end points.

VI = 19 watts

V = IR (Ohm's Law)

so V = I *24,

so VI = I^2 * 24 (multiply both sides by I),

Now we know VI = 19 watts

so 19 = I^2 * 24

so I^2 = 19/24, I = sqrt(19/24) = 0.9 Amps current that needs to be transmitted across the cable

Now we can finally work out the voltage drop across the 1200FT (600FT loop) cable:

V_drop = IR = 0.9*24 = 22V voltage drop.

SO, IF the Vi2401 runs at 48+22 = 70V DC - all should be good!

Regarding getting great 100Mbps throughput across the single pair of UTP - this is easily achievable using VDSL2 modulation/data transmission schemes, which can achieve 100Mbps at 1600FT across phone cable (Cat5 >>> phone cable).

Just want to clarify: Power = VI, measured in watts - this is why VI = 19 above


Yes, Basic Electronics 101 (I passed that course in 1967, LOL) (God, I'm an old fart). I didn't bother to measure the DC resistance of the CAT5 because the thought didn't occur to me. By the way, there are also two "66" blocks in the loop (one at each end of the 25-pair trunk). Add in the resistance of anything else in the loop: two patch cables, four RJ45's, etc.