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Normal mode helix antennas offer a solution for HF mobile operators facing significant height restrictions, such as those parking in indoor garages with limited overhead clearance. This design, adapted from concepts typically applied to VHF/UHF rubber duck antennas, allows for extremely shortened HF radiators that remain effective for county hunting and general mobile operation. The resource details the construction of a 20-meter helix antenna, approximately 10 inches long, wound with #14 AWG THHN wire on a 1 1/2-inch CPVC form, mounted on a standard 3/8 x 24 antenna stud. Mark Herson, _N2MH_, shares his experience developing these antennas, including initial research from the _RSGB VHF UHF Manual_ and practical winding experiments to establish the relationship between turns and resonant frequency. He provides coil data for various frequencies, emphasizing that these measurements were taken with an _MFJ-259a_ antenna analyzer and are dependent on the vehicle's grounding system. Despite their shortened nature, N2MH confirms the antennas' operational effectiveness, citing contacts with KL1V in Alaska on 20 meters and E-skip contacts on 10 meters. The design prioritizes continuous deployment without removal, making it suitable for operators who frequently navigate height-restricted environments.

This circuit enables fair copy of strong 444 MHz signals, off a local repeater, using a 2m rig and a 1/4λ 70 cm indoor ground plane antenna.

This web page offers an online antenna designer tool for hams to calculate the dimensions needed to construct a J Pole antenna for any desired frequency. The J Pole antenna is a simplified version of the Slim Jim antenna, radiating and receiving signals in an omni-directional pattern. It does not require a ground plane, making it suitable for indoor mounting. With the ability to be made from common household wiring, this antenna performs well for both receiving and transmitting purposes. The calculator is based on radio waves traveling at the speed of light and provides metrics in both imperial and metric units.

This article by Fred Delaney, K1DU, details the construction of a J-Pole antenna using 450 Ohm ladder line, designed for operation on the 2-meter (144 MHz) and 70-centimeter (440 MHz) bands. The design is based on an earlier concept using 300 Ohm TV twinlead by KD6GLF. The J-Pole is presented as a suitable indoor, freestanding antenna, particularly useful in areas prone to lightning or for hams with antenna restrictions. It can also be configured for portable use, such as a backpack version for camping. The antenna is vertically polarized and consists of a ¾ wavelength radiator and a ¼ wavelength matching stub, operating as an end-fed half-wave antenna. It does not require ground radials and offers a gain of 2.4dB over isotropic. The article provides the formulas and calculations for the ¾ wave radiator and ¼ wave stub, using a velocity factor of 91% for 450 Ohm ladder line. Specific dimensions for 146 MHz are given: a ¾ wave radiator of 55 3/16 inches and a ¼ wave stub of 18 3/8 inches. Construction involves cutting a 57¾-inch piece of ladder line and stripping 4 inches from one end.