I am connecting 2 sites with PtP550 integrated radios. Due to direct LoS not being possible I have been forced to use a HoP. At the HoP site I have limited space available and also restricted power. Thus I have decided to directly connect the 2 radio units back to back via the PoE adapters. IS this advisable or should I rather connect the radios back to back directly on the mast via the SFP port?
You can do the poe adapters directly with a cross-over cable, but I would highly suggest a switch instead. Not sure if you use vlans or not but a small 4 port netgear uses 9w at 9v max. A cisco 24port 2960s uses about 60w at 12v We use cisco switches at our towers and uses a buck/boost regulator to provide the DC power for the cisco from our nominal 24v sites and 48v sites. No we do not use the cisco power supplies as they are a switch mode step down power supply that wastes a lot of energy, we hook them up directly on the inside as they are 12vdc inside. Havent had any issues yet and havent blown a 5a fuse.
It actually worked interconnecting them directly. The power feed on site is hecticly bad. None the less, we installed a little 1KVA UPS and it powers the solution perfectly, Thanks again for your advise and recommendations.
1kva is only about 850w (power correction factor changes based on load type, efficiency and amount of load. So this is worst case available watts) This will give you about 15hrs (closer to 12 but that is a UPS limitation not a battery limitation) of run time. For a site like that I would get a direct DC power injector (packetflux gigabit sync injector but no sync (unless you want /need sync at this site), configured to provide 802.3at power output and power it off a 48v 100ah battery bank with a 48v power supply. Good for 3 or more days and its not switching between mains and battery so not spikes/surges/switching sags at about a quarter the cost of an active UPS. Also since your not up converting to then down convert the power those losses are removed. The extra heat is not being produced so you dont have to get rid of it either.
802.3at is nominally 48v but it is 56v (48v battery charge voltage), this does work as I have an IP phone at a tower running on 48v even though it requires 802.3at.