Ham Radio Help Desk

Virginia hikers and hams supported the White Rock Cliffs (Station #6) of the first Annual Golden Packet Event.

Summarized, we were trying to set up APRS relay stations up and down the east coast to cover and service all points along the Appalachian Trail and surrounding areas. Some RF link analysis was performed and is available for viewing at http://www.packetradio.net/events/AT_Golden_Packet_Event/ using the remarkable Radio Mobile program and A LOT of SRTM elevation data.

Of the fourteen stations planned several points were accessible only by foot. The White Rock Cliffs station was no exception.
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Type “J-Pole” into any search engine and you will see dozens of not hundreds plans to build your very own J-Pole antenna. Many are variations on the tried and true 1/2 wave design with the 1/4 wave stub at the bottom. Be it a plumber’s delight with copper pipe or ladder line heaven using a trimmed up 450 ohm feed line, many folks have successfully created their own J-Pole antenna with a surprising variety of materials.

However, there appears to be some kind of mystical attraction to the 5/8 wave radiator. Several of the J-Pole designs attempt to make the radiator 5/8 wave in length and adjust the phasing stub to make for a good match.

Let’s compare the two approaches using the models available from the late Larry Cebik’s NEC collection. Here are the contenders each using 3/8 inch diameter copper pipe…
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While planning for a ham radio hike into the mountains to support the Appalachian Trail Golden Packet exercise, I asked my club members for ideas about a good portable 2 meter antenna.

One response included a link to this web page showcasing a collinear J-Pole antenna using two 5/8ths wave antenna elements.
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In a previous post we debunked the 2 meter 5/4 wave antenna as actually an end-fed full-wave antenna resulting in a poor radiation pattern hardly optimal for terrestrial use. The fix was to turn it into a collinear with the addition of a 180 degree phased stub between the two half-wave sections.

Thus, the 2 meter 5/4 wave antenna is bunk… or is it?
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Many makers of J-poles for 2 meters claim they can also be used at 70 cm.

It may not be intuitive at first, but the answer, at least from an antenna pattern standpoint, seems to offer some hope.
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A friend of mine is preparing for the upcoming Virginia QSO Party in March 2009. Part of the preparations include a focus on some good VHF antennas to support the heavy use of VHF mobile operations in this party. Vertical polarization is key to success. He spoke of a 5/4 Wave Antenna.

Unfortunately, one web site promoting a 5/4 wave antenna solution failed to realize you can’t make an antenna longer without eventually hitting a limit.
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