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  A Reduced-Size Half Sloper For 160 Meters

By Don Kirk (wd8dsb)

My original article "A Reduced-Size Half Sloper For 160 Meters" first appeard in the March 1998 issue of QST, and then it was reprinted in the ARRL's Wire Antenna Classics 1st addition and the ARRL Hints and Kinks 15th addition.

• • QST March 1998 (Pages 54 through 56)

• ARRL's Wire Antenna Classics 1st addition (Pages 7-7 through 7-9)

• ARRL Hints and Kinks 15th addition (Pages 7-13 through 7-15)

Download Original QST article here: https://drive.google.com/file/d/1M_lOa1KgcI4qq4LdPmAHmJAGREm5AlxA/view?usp=drive_link   

(Posted with ARRL/QST permission; copyright ARRL)

Note : There was a typo in the original article.  The 90 turn coil will have a length of approximately 4 7/8"  long, not 4 1/2".

Measured Coil Resistance and Power Dissipation Calculations (28OC13)

Measured Loading Coil ESR (Effective Series Resistance) at 1.8 Mhz = 3.9 ohms

Assume feedpoint impedance = 50+j0 ohms, and Power Out = 100 watts, then I = 1.414 amps.

Coil Power Dissipation = 1.414 amps x 1.414 amps x 3.9 ohms = 7.8 watts

Note: Measured SRF (Self Resonant Frequency) = 8.3 MHz

The coil is designed to provide the correct amount of inductive reactance to make the combination of the 68 foot sloping wire and the coil to be the equivalent of an electrical 1/4 wavelength at 1.8 Mhz.

The actual inductance of the coil is approximately 44.2 uH which provides an inductive reactance of 500 ohms at 1.8 Mhz.

Alternative coil designs

Using 18 Gauge Wire & 3/4 Inch PVC pipe (outside diameter of pipe = 1.05")

Number of turns = 81 (tightly spaced)

Coil approximate length = 3 5/8 inches (3.625")

Using 14 Gauge Wire & 3/4 Inch PVC pipe (outside diameter of pipe = 1.05")

Number of turns = 117 (tightly spaced)

Coil approximate length = 8.0"

Using 16 Gauge Wire & 1 1/2 Inch PVC pipe (outside diameter of pipe = 1.90")

Number of turns = 38 (tightly spaced)

Coil approximate length = 2.125"

Using 14 Gauge Wire & 1 1/2 Inch PVC pipe (outside diameter of pipe = 1.90")

Number of turns = 44 (tightly spaced)

Coil approximate length = 3.125"

Using 12 Gauge Wire & 1 1/2 Inch PVC pipe (outside diameter of pipe = 1.90")

Number of turns = 51 (tightly spaced)

Coil approximate length = 4.5"

80 Meter Reduced Size Half Sloper Design

If using 3/4" PVC pipe that has an outside diameter of approximately 1.05 inches, here are two different combinations that would work.

If using 16 gauge enamel coated wire:

3.5 MHz Design: 54 close spaced turns, coil length approximately 3.0 inches long.  Sloping wire = 35.15 feet

3.8 MHz Design: 49 close spaced turns, coil length approximately 2.75 inches long. Sloping wire = 32.38 feet

Inductance for the above two coils will be approximately 22.74 uH

If using 14 gauge enamel coated wire:

3.5 MHz Design: 64 close spaced turns, coil length approximately 4.5 inches long.  Sloping wire = 35.15 feet

3.8 MHz Design: 60 close spaced turns, coil length approximately 4.25 inches long.  Sloping wire = 32.38 feet

Inductance for the above two coils will be approximately 20.94 uH

Web page created and maintained by Don Kirk wd8dsb@aol.com