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September 1, 2004
First bicycle mobile ride
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Antenna is my new homebrew "very short endfed halfwave" for 17 and 20 meters. It is 13 feet long, coil-loaded and supported by a fiberglass fishing pole. I tried it out a few days before, mounted on the bike in the front yard. Made a 20 meter ssb contact to Washington state and received an S-5 report with my five watts. KO3G/7 was an S-8, but was running 700 watts!
To keep the maximum height under the 13.5 foot legal limit, I sloped the antenna back. It appears to work just fine.
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Just a few minutes after the photo was taken, I was a block from home and making my first QRP bicycle mobile contact with KC5IJP in Mississippi!
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I weighed my options between having a 13 foot 1/4 wave antenna or staying with my usual shortened halfwaves. With a 1/4 wave, I suspect the bike is only a fair groundplane, and the maximum current point (and therefore the max radiation) is at the base, just over two feet above ground in this case. With the 1/2 wave, it has been quite shortened from full size, but needs no ground, and the maximum radiation point is eight feet above ground. I thought I would give it a try.
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I found the camera bag at a garage sale for 2 dollars. That's my FT-817, sitting on 4 inches of foam. Below that is the headset adapter. Later, I will add an external speaker in that top, zippered pocket along with a clock and digital voice recorder wired to the microphone cable to keep an audio log of my contacts. Some of the foam will be replaced with the Z-11 tuner for when I build a center-loaded 1/4 wave antenna on 40 meters. A pre-made 6-foot BNC-BNC coax cable just reaches from the rig to the antenna in the back.
The bag rests on a coated piece of 7" x 7" plywood, and that is mounted to the handlebars with aluminum brackets: rubber from an old inner tube is sandwiched in between for more shock absorption.
I discovered that I need to rebuild the headset interface, with a PTT button on the handlebars. I used VOX tonight and it worked, but it was also activated every time a car went by.
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The antenna is mounted to the bike with an assortment of PVC pipe fittings. the support is made from a 3/4" tee, two elbows and pipe. the antenna rests on a riser made of 1/2" PVC pipe. all the PVC was painted black and given a coating of Polyurethane. The whole thing is held to the bike with hose clamps.
The blue box is a homebrew high-Z matching unit.
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Continue down for one more picture...
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Here's a close-up of one of two coils that make the antenna an electrical haldwave. Using the full coil, it is a 20 meter antenna. With the alligator clip connected to the tap, it is set for 17 meters.
I used 20 gauge insulated stranded wire, wrapped around some thin-walled 1.25 inch PVC pipe, then covered it with electrical tape.
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Since creating this page, I have refitted the bike with an IC-706. On June 11, 2005, I worked ZL1AIX in New Zealand while I pedaled near Golden, Colorado! Here is a page with a photo and an audio sample:
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