Category Archives: Antennas

QRP: A (minor) star on Kon Tiki!

I watched the 2012 movie adaptation of the 1947 documentary, Kon Tiki, made by Thor Heyerdahl of his famous balsa wood raft adventure from Peru to Polynesia. The movie was nominated for an academy award and it’s easy to see why. Very well done with some amazing special effects work. I had no idea that for the trip, Heyerdahl’s crew included not one but two radiomen! The film shows the radio receiver, key and headphones used. I wasn’t able to determine the receiver manufacturer, but it looks like they used a J-38 key. Power seems to have been provided by a crank-powered generator of some kind.

During the crossing the movie includes several scenes of the radiomen struggling to get antennas working. In one scene they attempt to get an aerial in the air with a balloon even. Ultimately they appear to have settled on a simple long wire hoisted up along the mast.

The radio is used to report their position during the journey and when they ultimately reach Polynesia you hear the sounds the the BBC coming from the radio and see one of the radiomen cranking the power generator.

It seems likely this would have been a QRP operation start to finish.

The movie is definitely worth watching. I caught it on Netflix.

Magnetic loop antenna update

Did more in-depth reading on magnetic loop antennas and have decided not to move forward on building one. What changed my mind were reports that pointed out high RF radiation associated with MLAs and the potential for accidental exposure unless the operator remains at a sufficiently distance from the antenna (3-6 feet at a minimum), even when operating at QRP power levels.

That, and the associated very high voltages associated with these antennas, could make a MLA a bit more dangerous than I prefer, especially for operation inside my home where proximity to the antenna, for tuning purposes, could cause me to position myself too close to the antenna.

Gray Line Propagation to Europe on 20m

June 9-10 have seen good 20m propagation to Europe around 0430Z.

June 9: worked F2GL and FG8NY and DF2PY. June 10: worked LY2BAW, and EW8O.

This evening heard, but did not work, LZ1534GWS, SM5COP, 9A2HF and OH4RF. Signal strength around 5 for those stations.

All these on the new home brew indoor 40 ft loop antenna mounted on the ceiling at about 25 feet above street level.

Phase 1: St. Louis Micro Loop antenna

I decided against using a bicycle wheel rim as the antenna and opted instead for a copper loop design. The local hardware store sells soft copper tubing ($25) like that used for residential water and natural gas hook-ups.

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The bicycle wheel rim came in very handy as a form to create s near- perfect circle for the loop.

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Shaping the half-inch soft copper tubing was very easy.

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I’m trying to locate a 10:1 reduction drive for very fine tuning, but so far have not found a source.

Once the two-gang air variable capacitor with planetary 6:1 drive ($27) is delivered I can attached it to the loop, then mount the unit to a sturdy platform for fixed and mobile operation.

Inspired by the St. Louis Micro Loop II

The June 2013 issue CQ Magazine features a great article entitled, “Parking lot and dining room antenna ideas.” In the article, Dave – NF0R – talks about his St. Louis Micro Loop II antenna built from an aluminum bicycle wheel and an air variable capacitor. This magnetic loop is highly portable, light and requires no assembly for trail operation, especially if you’re already on a bike! I plan to set mine up for quick mount/unmount on my rear bicycle rack.

That said, I plan to use my Micro Loop for fixed and mobile operating. I ordered an air variable capacitor from Crystal Radio Supply in Texas and plan to use the aluminum front wheel of my Dad’s old 10-speed touring bike for the loop portion of the antenna.

I’ll post updates later after construction and testing are completed.