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Home of the Mystery Antenna |
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Can RG-58 [or any other coax] be substituted for RG-8X (mini)? Theoretically it should work, at least electrically. The main concern is the “strength” of the smaller wire. A portable Mystery Antenna using RG-174 is in the planning stage. If anyone has tried using different cables, please pass along your thoughts and observations for posting on this website. [Note: disregard velocity factor (VF) of coax-it is not applicable in my design]
Can I use twin lead or open wire line directly to an antenna tuner in lieu of coax and a twin lead stub? Absolutely. The twin lead stub is only necessary to give the antenna its multi-band characteristics.
How can I determine the “twin lead” Velocity Factor? The best way to determine velocity factor is to ask the distributor or manufacturer. It is very important that the correct VF be used in calculating the length of the twin lead. 300 ohm ribbon is a good choice. There are numerous types available. The VF range from 80 to 90 percent-for 300 ohm line, which means the half wave line could be anywhere from 26.4Ft to 29.7FT. 450 ohm ribbon line typically has a VF of 95%, which means the length should be 31.35 FT. The ARRL Antenna book list VF for different lines. [Note: Use 33 feet as the 20 m half wavelength for the above calculations.]
Should I use a balun? A balun is unnecessary and will only degrade performance. A line isolator between the end of the twin lead and the coax is recommended. It helps minimize feed line radiation and stray RF, which can cause problems in the shack. [Note: The original article recommends the use of a 4:1 balun for a mono-band version of the Mystery Antenna; however, a balun is no longer recommended. Instead, try a quarter wave 75 Ohm matching transformer. RG59 (Beldon 8241) is a good choice. A section of 75 ohm cable cut for 20 meters—10.89 feet can be used with the the multiband antenna. It will lower the SWR on 20 m to close to 1:1 and is transparent on the others bands.]
I get higher SWR readings than appeared in your article, am I doing something wrong? Probably not. SWR is a function of several variables to include wire and cable type, height above ground, etc. The best measure to ensure the antenna is constructed correctly is the 20m SWR. It should be under 2:1 across the entire 20 m band, and if you use a 75- OHM match transformer (see above) closer to 1:1.
Can I install the Mystery Antenna as an Inverted V? Absolutely. There are thousands of Mystery Antennas in use in many different configurations. Feedback from builders indicates that the antenna is very forgiving and will work under almost any condition to include indoors and with the ends bend.
Where can I buy a Mystery Antenna? The W5GI Mystery antenna is available as a kit from the Wireman or, if you prefer, direct from W5GI ready to install for $100 shipped within the U.S. W5GI can also build mono-band antennas for any band 40 to meters. Call or email for a cost estimate.
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