Thu Sep 11, 2008 5:56 pm
Interesting reading. Here maybe a sollution but not for all.. In my environment I cannot tolerate any noise from those dreadful smps units hammering away at 20-40 khz spreading harmonics all over the HF spectrum via ethernet cables that run vertically up a tower.
Also am reluctant to run 220 volt up a tower.
But try using centre tapped isolation transformer running with output at 50-0-50. Getting a shock between 50v and 0 aint so bad as 240.
Then use a power supply at the top that is not SMPS. A standard regulated supply or even crudely regulated at around 18 volt might do. Make sure that it is for 110 volt primary.
Then like as you do in this country, the overhead lines get struck nearby and the Line goes wildly high, sometimes 2 or 3 times 220volt.
At least the supply will then either double to 36V or worse case 54volts. I am sure that the primary secondary isolation within the transformer would be tolerant.
In this scenario, the routerboard is not stressed.
Then back at the power supply, use MOV transient supressors across the supply rails that will clamp at double the volts.
Use antisurge fuses before hand to tolerate the momentary clamp.
In my case I do not intend to use the POE via LAN, infact I intend to "lift" the LAN or isolate it by using 8 pin DIL relays. This way the LAN also wont radiate noise back down the tower:
The PSU at mast end, energises the relays too and lifts the LAN. But just incase the power supply fails, the relay then closes and the LAN becomes active. The Routerboard can then be reactivated by POE over LAN1.
Of course in my situation, the RB433 with 5.8g card and 2.4g card are just used as a repeater site, with no customer using the hard wire LAN:
Regarding lightening, try using the methods used by commercial broadcast engineers. Never have an antenna like the type we use immediately on top. If it is possible to use panels just below tip of mast, so much the better.
Use conductive guys above the antennas to dissipate the charges through the guys to a ground mat. Never allow the ethernet cables to come into contact with the mast. Run ethernet on its own up the centre of a tower and isolated from the legs. Same applies to coaxials.
There is stacks ofstuff around on that ttopic.