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 Previous: The K7RA Solar Update |  Next: Merle Glunt, W3OKN (SK) |
Stan Horzepa, WA1LOU
Contributing Editor
March 21, 2008
I get thrown for a loop again, but this week, it’s a current loop rather than a vintage one.
Craig Healy, NG1U, read last week’s Surfin’ that was all about Gordon Nelson’s Altazimuth loop antenna. He wrote that there are better ways today. A couple of problems with that loop design are the requirement for tuning and the inability to mount it outdoors, i.e., weather proofing.
Broadband loops will null just as well and don't require tuning. Simply use a preamp such as the DX Engineering RPA-1 to make up the gain. Modern receivers are robust enough that RF-stage preselecting and tuners aren’t really needed.
Two loop types I have used successfully are a single turn copper tube loop and a large ferrite rod. Here are two pages on the AM DXers Web site that explain them: the Cooper Loop Tube Web page and the Large Ferrite Loop Web page.
The ferrite rod antenna works well on 160 meters, but is “lossier” on 80 meters. I will be testing a more appropriate ferrite rod material that will soon be available; it is supposedly good up to at least the 20 meter band.
The copper tube loop with a dual pickup and phaser can produce some exceptional nulls and works well through 80 meters. The dual toroid/phaser approximates the tilt of the Altazimuth. I was easily able to null local 5 kW WHJJ-920 to hear a Canadian station at listenable levels. It also has the advantage of being very easy to build. Wind five turns of wire on a ferrite toroid core, solder four plumbing elbows and you’re done. A simple clamp arrangement attaches it to a camera tripod.
These same loops can be phased against a single whip for a cardioid pattern. The DX Engineering phaser works a well for this.
Until next time, keep on surfin’!
Editor’s note: Stan Horzepa, WA1LOU, got his start in radio chasing broadcast band DX with a crystal radio kit. To communicate with Stan, send him e-mail or add comments to his blog. By the way, every installment of Surfin’ is indexed here, so go look it up.
| Previous: The K7RA Solar Update | Next: Merle Glunt, W3OKN (SK) |
