FlightAware Discussions

What is the maximum length for POE with Cat 5 cable and POE hat?

I’m going to try POE for an AIS receiver (marine traffic), and I would like to know what is the max distance that POE via Cat 5 or 6 cable will work with a RPI. I only need about 50 ft. of cable

What is the recommended length to have reliable power and data transfer? What would be the max distance that will power the PRI?

Thanks, KB4ERT

I tested 100’ of cat5 using a dlink PoE switch and a tp-link gigabit splitter and it worked for piware used Pi 3B+ just fine.

The most important piece is gonna be the 5 V power supply you use.
The voltage drop over the Ethernet cable is usually not relevant.

The 5 v power supply takes the normally 40 V from the Ethernet cable and converts them to 5 V.

Would be best to have one that’s adjustable to 5.1 V but that’s probably impossible to find.

I plan to connect the Cat 5 cable to a WiFi extender inside a building with good wifi signal to an outside building with no power (30 ft.) where the RPI will be located. From the RPI a coax will go to the VHF antenna. So, should the Cat 5 cable power the RPI without a problem? I think the RPI will work fine at 5 V and doesn’t need 5.1 V as it doesn’t run a ADSB system,
It will use a dAISy hat for AIS reception. Any insight is appreciated.

Thanks, KB4ERT

There are PoE systems that can deliver quite a bit more power than a RPi could ever need.
Just get an appropriate one, the cable is not the bottleneck.

If the voltage drops just a little below 5.0V, the CPU will lower the frequency automatically to 400-600MHz - it happend to me. Basically you are wasting money on a Pi3 at that point.
The dAISy hat will add it’s own current draw to the Pi3 CAT5 power converter, but not that much.

The main issue will be the heat outside, added to whatever cooks inside that sealed box. it will toast the Pi3 with the hat on.

Why all this complication with PoE and installing electronics outside when AIS (162MHz) travels very well over 50 ft of coax cable?
You can add a CATV amp at the antenna if you really are worried.
I am sending ADS-B (1.1GHz) over the same distance (with a preamp) without issues.