49 lines
3.3 KiB
Plaintext
49 lines
3.3 KiB
Plaintext
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PIRATE RADIO SURVIVAL GUIDE
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Note: this chapter is from the book "Pirate Radio Survival Guide" written by; Nemesis of
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Radio Doomsday, and Captain Eddy of The Radio Airplane. If you like this book and would
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like to support their efforts, you may send a donation of your choice to either Nemesis or
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Capt. Eddy at PO Box 452, Wellsville NY 14895.
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Please note that some chapters refer to illistrations or drawings, these could not be included in
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this BBS version of the book. If you would like the illistrations or have other questions you
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may inquire at the above adddress.
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TRANSMISSION LINES
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Any antenna that you are going to connect to your transmitter MUST be done through the use
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of a feedline. Feedlines can be either one of two types, the more common co-axial line and the less
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common open type.
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Co-Axial feedline, or simply referred to as COAX, is the most commonly used and is perhaps the
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safest and easiest way to get your RF to the antenna. With all feedlines there are several
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determining factors that should be considered before you go out and buy your coax. First, and
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most important, is to look at your transmitters manual and see what IMPEDANCE LOAD is
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recommended. Some transmitters can "load" into a variety of impedances and some transmitters
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will only work correctly with certain impedances. The most common impedance is 50 Ohms.
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Right now, you should not be concerned with the How-To's and Why's of antenna feedline
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impedances. The second concern is the RF power rating of the transmitter. Feedlines are rated in
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both IMPEDANCE and POWER HANDLING, so it's important that you know what you need.
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For 99% of any type of transmitter/antenna combination you will probably encounter the most
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generic and all around used coax is RG/8U or the same spec, but smaller RG/8X. Some prefer the
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RG/8X because it's smaller. RG/8U,X impedance is 50 Ohms and can handle up to 1000 watts.
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Buy quality cable and not the cheap Radio Shack stuff!
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There is no critical length to use with feedlines, just keep the length of coax between the
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transmitter and antenna as short as possible to avoid losses. The more feedline, the more power
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you will lose before it ever gets to your antenna. Usually, losses are not apparent until the length
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of the feedline gets to be 100 feet or longer.
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The Outside end of your coax that connects to the antenna, you should take great care to seal
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the end to prevent moisture entering the coax! Use lots of electrical tape, silicon sealer, or COAX
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SEAL tape. The capillary action on the outer braid of your coax cable will actually draw water up
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through the entire cable. I have seen water come out of coax cable that looked like it was a
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garden hose! Once your coax becomes water logged it's
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pretty much useless, but can be used for ground connections in your station! You will also need
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a medium duty (Several 100 watt) soldering iron for soldering COAX connectors. PL-259 types
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are the most commonly used and you should ask for silver plated with teflon insulators to get the
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best connectors. Again, if you buy the Radio Shack cheapies, they could turn out to be more
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trouble than they are worth!
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