KI6CQ Station in Tennessee
Icom gear for HF and VHF
The Bamboo/Pizza Pan Helix
After 5 years of use, the M2 70cm antenna was acting up. I probably needed to replace the matching cables and give it a good tune up with the antenna analyzer.
But, I had been wanting to build a helix.
For materials, I had a fair amount of bamboo sitting around and a spool of 12ga solid insulated wire.
The first prototype was a little over a meter long and involved an aluminum baking sheet as the reflector.
But according to an AEA analyzer I could not get it to match on the 70cm band until I added this strange shaped shorted stub:
Once matched, this was fine for receiving the FO-29 downlink (without preamp) when the satellite passed overhead.
There were several flaws with the initial prototype. It wasn't level, The feed apparently wasn't correct. The reflector was not intended for outdoors.
For the 2nd version, I wanted a sturdy transmit capable 70cm antenna to replace the M2. So, it was time to scale up, and be a little more careful with construction.
To scale up, I would need a sturdy reflector. I looked at buying a copper disc from some online metal fabrication shops. They wanted over $100.
Surely something could be had for less than $100. But where could one obtain a round metal plate? Do people cook anything large and round? PIZZA! Looking around in the Wal Mart, I found Pizza Pans for $3. I thought, I say thought, they were aluminum. There was an aluminum mesh pan for $15, and while sturdy but I didn't like the idea of drilling round holes through the fine square mesh. And, for $3 the price seemed right.
Once I had the reflector home, I noticed something: it was quite difficult to drill. I don't recall Aluminum ever being this tough to drill. A gnawing feeling bugged me. I took a magnet out to the reflector and it stuck. Darn. This isn't Aluminum, it is steel! Could I use steel? Would it work?
In practice some of the larger TV transmitting dishes seem to be steel. I also read online where some hams were using steel wire instead of copper for long beverage antennas. Someone actually went to the trouble of calculating the loss in 100 foot of steel wire as compared to copper. The other problem, of course, is that steel rusts, but so does copper. Al is sorta-already rusted, it happens quickly and Aluminum oxide is not brown.
If you look to your left side you will notice a "precision feed" that uses a particular length of 1" copper strap as an impedance transformer from the helix impedance down to the 50 ohm N-connector and coax. This impedance transformation is sensitive to copper strap height above the reflector surface and is controlled by two MapCo gas station discount cards. These green plastic cards would otherwise provide a customer discount of a few pennies per gallon and help the store track everything you purchase -- this seems a much better use for them. The cards that secure the strap are themselves secured on non-conductive hardware that goes into a tapped threaded hole in the reflector. This allowed for adjustment of the height of the strap during testing.
Here's the full size helix in the final phases of construction and testing:
Looking Down the Barrel
Mast to Boom plate is a Wal Mart polycarbonate cutting pad sawed to size and attaches to two of the bamboo arms with outdoor quality zip ties.
The U-bolts are special fiberglass U-bolts made by Unistrut and sold in small quantity online by Eberl Iron Works.
This was fun to take out in the driveway or just point out the garage door at FO-29, receiving on an ICOM-706 in-a-toolbox pictured below in beach duty. I am sure the neighbors thought I was nuts.
As I mentioned, steel rusts. Here is what it looks like 7 months later, but.... it still worked well enough to make FO29 contacts into California and some 100 mile terrestial contacts in the Sept 2013 VHF Contest.
Ditched the bamboo for lumber.
Dual band. Assumed the two co-centered helices don't interact with each other. Final result gave measured crosstalk <1w out for 100 w in (<-20db). Also have external bandpass filters for 2m and 70cm in the shack. Turned out ok so far.
Here it is being prepped in the garage, with the 70cm winding finished.
The 70cm winding has a 12cm radius. The 12 gauge solid wire required supports every half turn.
Adding the 36cm radius winding for 2m required supports every quarter turn.
KI6CQ in California 2007-2010
Van picture above is from Mt Laguna, California contest trip with Raymond Moberly, AF6JS. We rented a cargo van and ran a 5 ele M2 beam for 6m, an 8 ele quad for 2m, and an 18 ele yagi for 430. Penninger drive over plate with "tipper" mast and snap joiners certainly made this easier to set up and take down. This site at about 6000 feet looks out over the desert hundreds of miles towards AZ. We managed to work several stations ground wave in AZ on all bands, even 432.
Another VHF contest operation as rover, shown here in the Mt Hollywood Griffith Obsevatory parking lot.
This is an experimental 15m single element quad loop made from a jackite pole and a bamboo cross arm. The white coil of wire below the feedpoint is a 1/4 wave transformer and balun made from 75 ohm RG59. This antenna did not need an autotuner, but was only usable on the 15m band.
The easiest way to configure the jackite pole was as a vertical. At the bottom I would place an autotuner and 2 radials. The 28' vertical element was a piece of thin black wire held to a rough vertical shape by gravity and the connection to the autotuner. This was usable on 40m-10m and sufficient to reach Hawaii and sometimes Australia and New Zealand on 20m or 17m within an hour or so of California sunset.
The vision behind the beach station was to make it possible for one person to bring a complete station out onto the sand from an automobile in only one trip. Multiple trips ferrying equipment is tiresome for casual operation, and leaving equipment unattended invites problems. The orange HF radio beach box contained of an Icom 706 Mark 2G bracketed to the side of the toolbox, with detachable control head; a 10Ah 14.4V LiFePO4 battery pack (with battery controller) in the alumnium case with yellow tape; a "Watts Up" DC power monitor for knowing how much of the battery had been expended, autotuner, coax and control cables -- in use, not shown. The toolbox could be carried in one hand, the jackite antenna pole and 28' vertical wire in the other. Water and beach towel would fit in a backpack.
The LiFePO4 battery, controller, and charger, cost around $100-$150. This kind of battery is less prone to dangerous thermal runaway than other lithium chemistries, and can be charged in one hour. Previous battery attempts included a 10ah 12V Gel Cell (too heavy!), and 10 D-cell 10Ah NiMH batteries in a long PVC tube (Sheriffs Deputies said it looked like a pipe b***), neither of which could be recharged in an hour. It should be noted that the NiMH cell had plenty of amperage to power the radio... the big rechargeable NiMH cells are not just for flashlights.
My involvement with ham radio began as a freshman at Caltech where I became involved with the club station W6UE. I was first licensed KB6KYB in 1985, then upgraded to advancedand was issued KI6CQ in '86.
Besides the contest-grade station W6UE, one of the perks of being at Caltech was access to nearby NASA/JPL. During the Voyager Uranus flyby their club, W6VIO, asked for volunteers to forward the probe's planetary pictures on slow scan tv and help operate special event stations on hf, vhf, and oscar 13 (AO13 had a highly eccentric orbit that provided a good source of DX and sometimes covered almost half the Earth).
Some years later, in graduate school, I became obsessed with packet, and designed an internet<->packet gateway for W6UE which ran from the tallest building on campus and served hams from orange county to N Hollywood. We provided two shared channels at 9600 baud, which because of hidden transmitters and other problems with sharing actually runs much more slowly. Of course now everyone has their own wireless internet router, with 1000x better performance, and ham radio is not involved. But I hope someday digital high speed ham radio data becomes revitalized.
With my freshly minted PhD in Economics, I took a break from ham radio for a while, coming back to it in 2004. I worked the occaisonal VHF contest with fellow Caltech alum Raymond Moberly, AF6JS from various parks and mountaintops in Southern California. Interests here also include LEO satellite and beach HF operation... and making bamboo full wave loops for the apartment balcony.
Recently I find myself back in Tennessee, where I grew up, and spending some time on HF with the ole 20m vertical dipole tied to a pine tree.
1262122 Last modified: 2014-09-14 21:37:13, 11703 bytes
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