Spring 2004 Issue

Chip Margelli, K7JA, testing a vintage Saturn 2-meter heavy-duty loop antenna that was bought new in the box for $6.95! (Photos by the author)

Omnidirectional loops are good, but the horizontal beam is better. That’s a fact: If you are going to squeak a long-range VHF or UHF signal to that station 1500 miles away through a tropospheric duct, the horizontal beam cannot be beat. If signals are coming in just above the noise floor from that distant tropo station, the beam will hear it, and even a stacked pair of loops won’t.
The horizontal loop has its place in the record books, however:
• Loop-to-loop mobiles over 2500 trans-Pacific miles
• 1500-mile beacon loop reception
• 1200-mile sporadic-E loop contact
• Loop-to-loop auroral contacts
Even the high-power VHF/UHF rover stations with their mobile beams rely on the loop’s omnidirectional characteristics with horizontal polarization to find mountaintop and desert hot spots. Just ask Pat Coker, N6RMJ, who uses his mobile loop as he drives from the desert to the sea, discovering multiple tropo layers as he heads up and down the mountainside.

Another loop-antenna user is airplane pilot William Alber, WA6CAX. “I run both a 2-meter loop as well as a 432-MHz loop on the belly of my Cessna, and I have hooked up with other 2-meter stations running a base-station beam up to 300 miles away,” comments Alber. “I also use the 2-meter horizontal loop for determining the upper and lower limits of the tropospheric duct between here and Hawaii. The KH6HME beacon that comes through every July and August is usually strongest when I enter the duct at about 1500 feet,” adds Alber, explaining that he can literally see the inversion layer where signals from the Hawaii beacon 2500 miles away begin to swamp his receiver.

When signals are strong from good propagation conditions, loops shine. For mobile in motion, loops are your solid answer for a horizontally polarized omnidirectional signal. Also, if you live in a condo or an apartment building where no outside horizontal beam is allowed for weak-signal SSB work on 2 meters and above, the loop is a superb choice.

The most simple, yet precise, configuration of the loop looks like a halo—electrically much like a halfwave dipole bent around in a circle or configured as a square, with a critical capacitive tuning between two to five picoFarad. The popular M2 antennas are formed in a square. The popular KB6KQ loop is formed as a halo. Both antennas have a proprietary sealed feedpoint, which keeps moisture from detuning the antenna in the rain. During loop testing, both the M2 and the KB6KQ loops are factory preset for the bottom portion of the band, where most weak-signal SSB and CW activity takes place. There is no need to fuss with tuning.
 

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