The Hustler 5BTV Conversion to 160 Meters
Dave Cuthbert, WX7G
any hams tell me they haven't tried the 160-meter band because they don't have room for an antenna. Well here is a one evening project that will let you give 160 meters a try and best of all it will fit in the smallest of yards. The antenna is basically a 22-foot tall top-loaded vertical that is antenna covenant friendly. (click for imperial/metrics chart) Just take it down in the daytime and put it back up at night when the band opens-the neighbors won't even notice it!
The prototype vertical is a modified Hustler 5BTV. The conversion allows the vertical to retain five-band operation by trading 80-meters for 160-meters. The conversion really revolves around the Hustler 80-meter 1-kW mobile resonator. This resonator, or loading coil, works on 160 meters by replacing the whip extension with a lightweight Top Hat. This resonator has an inductance of approximately 200 uH and a Q of about 175. To resonate this coil at 1.8 MHz requires a Top Hat capacitance of 40 pF. A drawing (not to scale) of the 5BTV with Top Hat is shown in Figure 1.
Top Hat construction is quite simple and is shown in Figure 2. I used 30-inch lengths of 3/32-inch diameter steel "music wire", available at hobby stores, for the spokes and AWG #28 wire for the perimeter wires. The hub is a 4" x 4" piece of copper clad printed circuit board with a hole drilled in the center. Copper adhesive tape is wrapped around the base of the spokes and the spokes are then soldered to the circuit board. The tips of the spokes also have some copper tape applied and the perimeter wires are soldered to these points. Leave the tuning wire off at this time. The result is a lightweight but rather fragile structure. Those of you who are more mechanically inclined are encouraged to come up with something a bit more mechanically sound.
To attach the Top Hat first screw the resonator onto the vertical. Then unscrew the resonator Whip Retaining Nut and remove the whip. Place the Top Hat on the resonator and replace the resonator Whip Retaining Nut. Lift the vertical into position and set it on the mounting pipe. Tune-up is simple and requires only your rig and an SWR meter. Check the VSWR at various frequencies until you find the resonant frequency. The VSWR should be less than 2:1 at resonance. The bandwidth of this antenna is only about 20 kHz so you will have to move in 5-kHz increments to find resonance. If the resonant frequency is above the desired frequency solder on the tuning wire and check again. Move the tuning wire closer or farther from the hub to tune it. If the resonant frequency was below the desired frequency simply move a perimeter wire in towards the hub to raise the resonant frequency.
The antenna is modeled over perfect ground per Figure 4 using NEC2. Note that the ground loss resistance is modeled as 12-ohms in series with the source and the coil resistance is modeled as 13-ohms in series with the coil. The input impedance at resonance is 34 ohms and the VSWR plot is shown in Figure 5. An antenna tuner works well for extending the useful bandwidth to over 50 kHz.
How does it perform? The radiation efficiency of 8% is decent for such a short antenna and using this antenna I placed 1st in Idaho in the 1999 ARRL 160-meter contest (low power class). Here are some tips for those of you who haven't worked 160-meters before. Most CW QSOs occur from 1805 to 1820 kHz while SSB operation occurs around 1860 kHz. Conditions are often best in the early evening and working 1000 miles will give you the same thrill as working the other side of the world on 20! -30-
Brief Professional Biography for Dave Cuthbert, WX7G
~ antenneX ~ January 2002 Online Issue #57 ~
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Last modified: December 31, 2010