Virginia ARES / RACES has experimented with hamstick dipoles and now recommends them as expedient, portable antennas for operations. The 2:1 VSWR bandwidth is narrower on the lower bands because the whips are proportionally smaller compared to the longer electrical wavelengths. Pairs of 20 meter whips on the Lakeview dipole mount measured about 100kHz, 40 meter whips 40khz and 75 meters about 20kHz. If your rig has an internal tuner the useable frequency span approximately doubles without a significant loss of antenna efficiency.
On-air comparisons were made between the portable whip dipoles elevated 20 feet compared to halfwave wire dipoles for 40 and 75 meters, the most common bands for daytime and night "short path," NVIS, EmComm operations. On 40 meters two whips were about 10dB (1-1/2 S-units) below the 40-meter dipole. Two 75-meter whips were about 18dB (almost 3 S-units) below the 75-meter half-wave dipole. This is no surprise since a 75 meter dipole is 130 feet compared to the 16 feet of the two whips. On 20 meters we were both pleased and surprised to see only a 6dB (one S-unit) difference compared to a G5RV antenna. Elevating the portable whips higher than 20 feet would certainly improve efficiency on the lower bands, but 20 feet is very suitale for short-path NVIS operations out to 300 miles, common for ARES / RACES applications on 40 and 75- meters.
Several of our members have used this system to check into the Old Dominion Emergency Net on 3.947 from condos or other antenna restricted areas. NB3O used hamstick dipoles to make contacts with European Russia on 20 meters from a condo in San Luis, CA. I used them while operating portable from an aid station in the Pentagon South parking lot at the Marine Corps Marathon last year and worked all up and down the east coast of the U.S., as well as Prince Edward Island, San Juan Puerto Rico and Mexico City, with good signal reports on the Intercon and Maritime Mobile Service Nets.
A variation used by NB3O provides dual-band HF coverage with a single feedline. Two Lakeview dipole mounts are bolted together with their center-isolated posts connected using #12 gauge wire and two sets of whips for 40 and 75 meters. There is minor interaction between the whips, although the #12 gauge wire looks slightly capacitive. Connecting the coax to the lower band dipole mount reduces the effective of the #12 gauge wire. A 25-foot length of coax is coiled at the base of the mast as an RF choke to reduce stary RF from coupling onto the shield. The samne could be accomplished by using ferrite beads oin the coax feed near the dipole mount. As with any transmitting antenna, ensure that the radiating elements, especially the ends, are kept safely away from bystanders!
While not as efficient as a full-sized wire dipole which is resonant for the frequency, the hamstick dipole is superior to a vertical antenna for short path EmCom on 40 and 75 meters, because it is horizontally polarized and provides the necessary high radiation angle for NVIS operations. It also provides an effective directional antenna on the higher frequencies, such as 20 meters, and is a very effective DX performer in that application for those who live in antenna restricted communities.
73 de KE4SKY
Virginia State RACES Training Officer