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Ethernet Errors when using Sync over Power

A common problem when using Sync over Power is the introduction of CRC or other Ethernet errors. These errors are typically a unwanted side effect of the inductive effects of the sync pulse. This pulse will induct a certain amount of voltage onto the data-carrying pairs of the CAT5 cable between the injector and the AP. This in turn, can corrupt the ethernet data in certain circumstances.

Fortunately, most of these effects can be reduced or eliminated. The following are common solutions to the problems of Ethernet errors with sync over power:

Use an appropriate surge suppressor: The number one cause of sync-induced errors is the use of an inappropriate surge suppressor for the application. An official motorola 300SS surge supressor is NOT an appropriate surge suppressor for this application. The 300SS in particular has a very low clamp voltage on the Ethernet pairs. So low that even a slight surge from the sync pulse will trigger the protection, shorting the Ethernet pairs. In some cases, power has to be removed and/or the surge suppressor replaced to restore service. Other surge suppressors have similar issues.

The following surge supressors are known to work with gigabit and sync:

  • McCown Technologies GIGE-APC-HV
  • McCown Technologies gige-twr-j-hv

Note that the above are both the HV versions. This is key to the operation of sync without errors.

Beware of bundled runs and/or multiple runs inside metal conduit, or alongside metal: We have observed that long tightly bundled runs is more prone to have problems with sync over power. In addition, running for any distance alongside ferrous metal (such as tied to a tower leg) tends to aggravate the problem as well. Most of the time, this type of run will NOT cause an issue, but if possible, limit the distance of bundled runs, and try to limit as much as possible the distance the cable runs alongside metal.

Use an alternate wire pinout: NO LONGER RECOMMENDED DUE TO INCOMPATIBILITY WITH GIGABIT ETHERNET!!! The standard wiring diagram for CAT5 results in both of the wires in the Blue pair carrying the negative power to the radio, and both wires in the brown pair carrying the positive power to the radio. To help reduce the surge potential from the sync pulse, it is possible to re-wire BOTH ends of the CAT5 cable between the SyncInjector and the Radio such that both positive and negative are carried on each of the pairs - thus helping to cancel out the surge. To do this, simply recrimp the cable on both ends such that Blue/White and Brown/White are on pins 4 and 5, and Blue and Brown are on pins 7 and 8. The remaining pairs are wired as per nomal on both ends. We recommend that you label this cable clearly so that someone doesn't come along later and re-crimp it the "correct" way.