PIRATE RADIO SURVIVAL GUIDE

Note: this chapter is from the book "Pirate Radio Survival Guide" written by; N Radio Doomsday, and Captain Eddy of The Radio Airplane. If you like this book a like to support their efforts, you may send a donation of your choice to either Capt. Eddy at PO Box 452, Wellsville NY 14895.

Please note that some chapters refer to illistrations or drawings, these could this BBS version of the book. If you would like the illistrations or have other may inquire at the above adddress.

SWR


Standing Wave Ratio or SWR is probably another mis-understood concept in radi tendency to mess up some people. While I'm not going to get extremely technical explain what SWR means and how you can cure High SWR readings.

SWR is a term used to measure the amount or ratio of RF Power that IS being r antenna to RF Power that is NOT being radiated and reflected back into your fee The actual formula to determine this involves some complex math and I'm not goi Instead, I refer you to the diagram of a typical station layout showing the tra RF path. If you see where the SWR/Power Meter is placed in the line, you can un able to measure this.

A perfect SWR is 1 to 1. This means that all RF power is being radiated by th and none of it is being reflected back. "What causes RF Power to be reflected b typically the cause of this problem is by using a Non-Resonant or Random Length can quickly understand the importance of using resonant antennas is to MAXIMIZE signal by actually radiating ALL the power you are transmitting!

"What happens to the Reflected Power?", It returns back into your transmitter finals to be dissipated as waste heat! This should be avoided if possible. In f solid state transmitters will shut down if the SWR becomes too high, in order t

As your SWR increases, your radiated power decreases. Typically, your SWR can 2 or 3 to 1 before any real problems start. To maximize your signal you should SWR below 2 to 1.

SWR/Power meters can be purchased easily and even the cheaper ones tend to wo as well as the more expensive models. There are several features available with You must make sure that the meter can handle the power level you are running! T meters will measure up to 1KW but not always. I prefer the dual meter type wher my FORWARD and REVERSE power at the same time. Any type of meter is fine as lon obtain and use one!

"How can I reduce the SWR of my dipole antenna?", In order to do this, you ne the RESONANT FREQUENCY of your existing antenna. Now, in the chapter on antenna discussed how to "cut" a dipole for the 40 meter pirate band, However, dependin antennas proximity to other structures and height from ground, the math used to length of the antenna is only a close approximation.



To find out just where your antenna IS resonant, tune up and check the SWR at across the 40 meter band. For example:

7000 Khz ......... SWR 3.5

7100 Khz ......... SWR 2.4

7200 Khz ......... SWR 1.8

7300 Khz ......... SWR 1.0

7400 Khz ......... SWR 2.0

7500 Khz ......... SWR 3.2


As you can see from this SWR plot, our antenna is RESONANT around 7300 Khz an LESS resonant (i.e. SWR increases) the farther we move away from 7300 Khz. To c problem, we would need to CUT wire, about one or two inches at a time from each dipole and repeat the measurements until we make the dipole resonant around 740 antenna were resonant around 7500 Khz. you would need to ADD wire to each end o dipole until you LOWERED the resonant frequency.

Now I would like to talk about Antenna Tuners or Matchers. A ANTENNA TUNER WI NOT MAKE YOUR ANTENNA A MORE EFFICIENT RADIATOR! "What?", you say! "With
my antenna tuner I can make my SWR 1 to 1 where before it was 4 to 1.", that's look at our station diagram, a antenna tuner only makes the standing wave 1 to and the transmitter! NOT between the tuner and Antenna! If you doubt this, move meter to the Antenna side of the matcher to see what is going on. The only adva antenna tuner is in the rare case you cannot erect a resonant antenna, a antenn transmitter load up into just about anything, but it is NOT and should NOT be u for a RESONANT antenna!

The last theory I would like to debunk is that of "Cutting Your Coax" to decr length of your feedline IN NO WAY will affect your SWR! Cutting or Lengthening accomplish nothing but wasting your time! Purists will argue this point and I w certain antenna applications, feedline length DOES play an important part. Even Buffs will tell you that for the most accurate SWR measurements, the instrument at even wavelength multiples in the feedline, or better yet,
right at the antenna feedpoint. These are true and much more difficult to accom the meter in line will give you a close enough reading to spot any troubles in feedline.




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