• I have two AIR-BR1410A-A-K9 bridges that I need to use for connecting a vehicle network to a building network. The bridge on the building will use the conventional mount and network connection. The other bridge is going on top of a vehicle (bigger than a UPS truck, smaller than an 18-wheeler). There are several existing coax runs from the interior of the vehicle to the roof of the vehicle. All runs terminate with an N connector inside and an NMO outside and are 50 ohms. I would like to use these runs for the bridge, but the F-connectors/coax for the 1400 are 75 ohms.

    Specifically, I want to put the bridge injector (which is also a media converter) inside the vehicle and use the existing vehicle coax runs so that I can easily mount/connect the bridge on the roof of the vehicle. I have the F-to-N and F-to-NMO adapters. What kind of trouble am I going to run in to running the Ethernet and power over cables/connectors with mismatched impedance? I'll try to step through the entire run:

    Ethernet 100Base-T and DC Power connects to the injector

    F-type coax (75 ohm) cables from injector run 4 feet to connect to F-to-N adapter (not sure what the impedance is here)

    F-to-N adapter connects to N connector at coax patch panel inside vehicle (50 ohm at panel connector)

    Patch panel coax travels approximately 40 feet to roof-mounted NMO connector (50 ohm)

    NMO-to-F coax adapter connects to NMO (not sure of the impedance here)

    F-coax runs 10 feet to Bridge (75 ohm)

    Will this work, or do I need to build a couple of transmatch stubs (I assume I would need one at each end)?

    I have a good RF guy working with me on this project, but we are stumped since the coax carries the ethernet and power, not "normal" RF signals.

  • I don't have any data to back it up, but impedance mismatches are a bad deal in any circuit. I wouldn't chance it, but if you want to try it is highly unlikely that you will burn out your transmitter (PoE?) with that mismatch. The problem is that in the short term it may work fine but the standing waves may damage the unit over time. Remember, 80% of all networking problems are at the PHY. Don't make yourself a problem that would be very difficult to troubleshoot later down the road.


  • Give these guys a call at their tech support number.I've always found them to be very helpful.

    Even if you are not using their products, they usually will answer any of your questions regarding VSWR and impedance matching etc.


  • Ethernet uses 4 wires out of the 8 conductor CAT5 cable

    POE uses 4 more

    and you are going to send this through 2 conductor RG59...?

  • @ad5mb - They use two coax cables (I think the kit includes RG-6 quad).

  • Thanks, everyone. If I actually attempt this, I'll let you know how it works out.

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