Digital Watchdog Starlight D1363D Informacje Techniczne Pobierz pdf (Strona 85)

Chapter 8

Wireless Practices

This chapter will focus on a number of pitfalls and ways to ensure you put up good links. Some things

will be glossed over a bit. For example, we'll discuss antenna selection, but there's little sense in

reproducing hundreds of pages of HAM antenna theory. We will, however, cover in depth how to set up

long distance links (the most difficult). So hold on to your hats.

Your radio

We've covered the basics (and more) of configuring your radio. But you're not quite ready to install it

on a tower. Before donning your safety belt or climbing harness, let's take a good hard look at how

you're going to power the radio.

Most of us are using POE. The WRAP cards are capable of taking power from the Ethernet cable or

from a plug directly to the board. When using POE, you must ensure two things: first, that your power

supply provides adequate amperage. What works on the bench may not work well under load. Your

first clue will be unexplained reboots during peak traffic loads. And second, keep your POE runs short

to avoid power losses on the cables. Powering the POE injectors directly from a marine deep-cycle

battery will ensure you have plenty of power available for longer cable runs.

It may be to your advantage to install a NEMA 4 enclosure mid-tower with a small switch and large

POE adapters inside and only bring power from the ground to the box (see also Your tower, below).

Your tower

This cannot be stressed enough. You must ensure adequate grounding for your tower and all systems on

it.

The tower itself should be grounded at each leg. You'll also want to have either a lightning rod with a

sharp point or preferably a static discharge device like the bristle brush looking devices at the top of the

tower.

No silver bullet exists to prevent lightning strikes and the damaging effects of ESD (electro-static

discharge). In fact, there are various schools of thought on the subject. But the advice this book will

give you is to ground everything as well as you can to a common ground. Take care not to end up with

a split ground. A split ground is two or more ground points at different potentials due to the time it

takes a lightning discharge to travel from one ground rod to the other (travel times are different through

different mediums).

The purpose of the lightning rod or brushes is not to attract lighting (as the name lightning rod

suggests), but rather to discourage the formation of a “leader” by dissipating an electrostatic potential

into the passing cloud slowly (thus the reason for a well-sharpened point on your lighting rod). The

more potential dispersed prior to formation of a leader (that first stroke of lightning), the better. Then,

any leader that does form will be much weaker potential. It is crucial that whatever device you're using

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Digital Watchdog Starlight D1363D Informacje Techniczne Strona 85