Clark, KE4RQ, asked: I installed a commercial multiband inverted V at my QTH and have had poor results for DX. It looks like a Windom design with the feedpoint off-center and comes with a balun to allow for coax feed. According to the specs, it should provide a match at 80, 40, 20, 17, 12, and 10, and the ATU within my K1 matches fine on 40, 20, and 17. (I've also had no problems matching other rigs using their ATU to the other frequencies). I am using a low loss coax from Davis RF and the rig(s) are grounded to a ground rod just outside the shack. The apex of the antenna is about 40 ft with each leg at the approximate height about ground that the manufacturer's specs require. It is strung in a NE/SW direction -- broadside to southern Africa. The antenna seems to 'hear' fine; it's in the transmitting that it appears to be deficient. I've tried to check into the Elecraft net with no luck. I tried to contact Peter One (using 100W I must admit) with no luck at all times of the day and night. Standing on my deck looking at the antenna and wondering what, if anything could I change, it occurred to me that perhaps my problem is that the antenna is significantly BELOW the housetop. How can that be, you ask? Well, here in Atlanta, I have what we call a 'ravine back yard'. My house is below street level and the back yard has a deep slope. The tree to which the antenna is strung is in the backyard and while the height above ground is 40', it is also at the eye level of my first floor (2 story house). The longest leg of the V is well below the house level and actually facing (for half its length) the concrete basement that holds up the house. Sooooo.....how much impact on the take-off angle would you think this configuration would have? Should I replace the V with a flat-top doublet at the same 40' height which would result in most of the antenna being at 40' but still below the roof level? ---------------------------------------------------------------------------- ----
Expect your strongest signals to be opposite the direction of the slope. That is, the ground sloping up to the house will act as a reflector. Actually, below a wavelength or two above ground, the ground ALWAYS acts like a reflector. That's why horizontal antennas at the right height - about 1/2 wave up - enjoy 4 to 6 dB gain over a vertical for fairly low angle radiation. Closer to the ground horizontal antennas see that gain straight up for short skip propagation. That's why folks currently call as a NVIS or near-vertical incidence system. In your case the ground isn't horizontal, but it'll work just the same. At 40 feet, the major lobe from your antenna will be opposite the ground, especially on 40 and 20 meters. Only in this case it's off at an angle opposite the slope of the ground instead of straight up. That's good for working stations in that direction, particularly DX and lousy for working stations in other directions beyond short-skip range. "Mountain topper" portable operators often try to duplicate your situation on purpose, erecting a low doublet or dipole off the side of a steep cliff to get low angle radiation from a horizontal radiator that is not very high off of the ground. Bottom line: your propagation will be greatly affected by that slope. Hopefully it points your signal in interesting directions even if that doesn't include Oregon for the ECN. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
