The 40-Meter Ground Plane Testbed On Canby
Photographed and Reported By Norm Styer - AI2C
BACKGROUND: Since the installation of Roadstar Wideband Service here at the Canby Road in December, I've experience considerable noise interference from the Roadstar Transceiver Unit that is mounted at the top the pole supporting my 2-element 40-Meter yagi. So before we can move the Roadstar unit, we're beginning to experiment with an additional antenna for 40-Meters.
TESTBED: I've had this 40-Meter ground plane antenna left over from the 2006 W3ZI Pennsylvania QSO Party Expedition to Red Hill. So up it went here. The MFJ Antenna Analyzer said it resonates best around 7130 kHz. In the shack the SWR was well under 1.7:1 across the band and both tuners took it to 1:1.
FIRST LOOK: First, the noise is gone. So maybe it's a dummy load and doesn't hear anything. But yesterday - 31 January - after tying it off, I worked a GJ on 40-Meter CW with 150-watts at 4 PM in the afternoon - well before our sunset. Than around midnight last night we put E51WWA on the South Cooks and VP6PR on Pitcairn Island, both in the South Pacific, in the log on 40-Meter CW. I was running a little power. I was able to do a little A/B antenna receiving testing. Well, the yagi might be the dummy load. Signals on the vertical were 1 to 2 S-units stronger and clearer. Sometimes their signals disappeared into the noise with the yagi. At the same time, there a nice signal - like S-8/9 from KH6-land; there was about a 2 S-Unit difference with yagi capturing less signal. In all likelihood, I would not have bothered to try calling them with just the yagi available. The lower takeoff angle is apparent.
Here are a couple views of the Ground-Plane Feed Point bracket:
NOTES ON SIMPLE CONSTRCTION. Build it from some 2- x 1/8-inch stock aluminum that is available at Home Depot in 4-foot length. Use stainless steel hardware from Tractor Supply. Make the hole large enough for the SO-239 coax cable mount with a round metal file after you drilled it out with a 1/2-inch or larger drill. Use Number 12 stranded electrical house wire that is also available at Home Depot. Cut all wire elements to 6-inches + 234/F (in MHz). The extra 6-inches is for mounting wire under 1/4-inch hardware and with some left over for tuning. Use a nice stand-off insulator to relieve the strain on the vertical element. Just pull it up in a tree. Of course, you want insulators on the ends of each element. Try to get the feed point up 3/8-wave above ground and spread the radials at a 45-degree angle. If done correctly you'll need no tuner for good operations within 50-kHz of the design frequency.
Use a 12-inch length of the Number 12 wire as a strain relief on the coax as shown. Rap several turns around the coax after you created a little drip loop. Using Number 12 wire makes all this very easy.
Add at least two tuned radials. More is better but two works.
So, We March On. A few more elevated radials and maybe up a little higher. I do intend to grow stuff this spring and plowing is coming up. By the way, that white rope on the left is my pull down for one end of my 160-Meter dipole.
More To Follow.....
Best Regards, Norm Styer - AI2C de Clarkes Gap - Canby - Loudoun - Northern Virginia