Digital Watchdog Starlight D1363D Technické informace stáhnout pdf (Strana 87)

protect them. All that said, Ethernet cables can pick up EMP when strung like a clothesline from a

client on a post in the yard to the house. Long horizontal Ethernet cable runs should be buried.

Antenna cables

Most folks deploying detached antenna systems opt to build their own antenna cables. After all, how

hard can it be? Unfortunately, many also opt not to purchase the proper equipment to build the cables.

While a crimper is essential, most believe proper cable strippers are not.

Any nick or cut in the center conductor will alter the characteristics of the cable. Many of you will

have heard at one time or another someone else on your telephone line. This is a result of near-end

crosstalk from a telephone cable that has nicks or gouges in the wires. The effects in the GHz range are

worse and include excess reflected power and poor impedance match. Ensure your center conductor is

not damaged.

Some folks also feel that the mechanical connection made by the crimpers used to crimp the pin to the

center conductor is not good enough, so they solder the tips on. While this may not be a bad idea,

using a too hot iron or the wrong solder is much worse. If you absolutely must solder your connections,

use a maximum 60 watt iron and resin core solder, not acid core solder. Resin core is for circuit boards,

acid core is for plumbing, and we're not plumbers.

When you're ready to connect your cables, you must ensure no moisture can enter the connectors. For

years most of us used 3M 130 or similar tape. This is high voltage rubber tape, not the plastic electrical

tape (if you are using that, throw it out). Some folks have also used a similar rubber compound that

comes in rolls or sheets and can be formed around the connector. But the best thing to use to keep

moisture out of connectors is STUF, an insulating dielectric compound. Just a small squirt into the area

of the center connector and you can forget moisture problems.

Finally, when installing your LMR-400 or LMR-240 cables, ensure your tie wraps are not so tight they

deform the cable. The electrical characteristics of the cable are altered if the distance between the

center conductor and the shielded braid is changed.

While some operators swear by the gel-filled LMR cable (LMR-###DB, the DB standing for direct

burial), as long as the outer covering is not damaged, water should not be a problem. Non-gel cable

should not be run underground or on the ground where it may sit in water. And installed cable should

never be removed and reinstalled at another site. Discard old cable, it's cheaper to buy new than endure

problems with old cable.

Antennas

If you glossed over any of the above as unimportant, please pay attention to this part. The absolute

most important part of your radio system is the antennas. You must choose the appropriate antennas for

the link you wish to make. All else being equal, a 25 dbi grid antenna will allow you to communicate

twice as far on half the power as a 22 dbi grid will. In general, you'll be better off with two 17 dbi

sector antennas and a splitter/combiner than with a 12 dbi omni. First you'll be able to focus your

(usually narrow) horizontal band better, but secondly, and more importantly, you'll be able to hear weak

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Digital Watchdog Starlight D1363D Technické informace Strana 87