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On Dec 11, 12:49 am, RHF wrote:
On Dec 10, 4:13 pm, wrote: I suspected there are many people who lurk but will never post in a public arena. After my experiences with a cyber-stalker I can understand their hesitance. A SWL in Scotland asked me about a comment I made regarding antennas in one of my RFI diatribes. Sorry for the delay, but I ran this past some friends of varying technical skill levels, to insure that first my answers are technically accurate, and as simple as I can get, while maintaining accuracy. Get the wood out to start the fire to burn me at. There are really only three types of HF antennas. Dipoles Loops Surface or Traveling wave. Of these, only the Traveling wave antenna relies on the earth below it for it't basic operation. Dipoles will be effected by the presence of the earth below them, but a dipole will operate just fine in free space. Loops are somewhat less effected by the earth, but they to will operate just fine in free space. A traveling wave antenna, beverage or 'long wire' relies on the soil below the elevated conductor. For most of us Beverages and true 'long wires' for anything below 30MHz isn't practical. We simply don't have the real estate needed to erect one. Loops are loops. Many people swear by them, but I have yet to be impressed. If you must have a loop investigate the WL1030 as it compares very well to the famed Wellbrook ALA1530. I owned a for a few weeks and in a head to head test with the WL1030 the WL1030 was always as good as or better then the ALA1530. The WL1030 specifies a hard to find Litz wire that shouldn't stop anyone. I tried the specified Litz wire and a solid and a stranded wire and I couldn't tell any difference. It is true that I didn't do extensive tests below MW. I am not into NDBs. The typical 50 to 100' random wire is barely a longwire antenna at 10M, but at 2M, 146, it is a true longwire. But it is also an extremely poor antenna at those frequencies. Now for the part that labels me a Apostate. - - The random wire antenna many of us use is a dipole in disguise. - The elevated wire is the obvious element. - The earth is the non obvious element. - The earth is generally a very poor conductor - and also has significant reactance. - Hence the Far-End-Fed Inverted "L" Antenna # 1 - One-Half - The Horizontal part of the 'elevated' Wire Antenna Element (-) is above the surface of the ground. Note - Grounding Point (g) at the Far-End-Fed Point using a Ground Rod mounted Matching Transformer (M%T). # 2 = The-Other-Half = The Horizontal part of the 'on-the-ground' Coax Cable (=) is On-the-Ground or Buried-under-the-Ground directly under the elevated Wire Antenna Element. {Unifying the Ground below it} -Sort-of-Like- a Crude End-Fed-Dipole x-----------------------------o | | | M%T===========================RX -g- IMHO - Generally works better than a Near-End-Fed Inverted "L" Antenna. ~ RHF . If I understand your diagram, the feedline, be it coax or balanced, either has a transformer or is directly connected so the antenna feeds the center of the coax or one side of the balanced line and the braid or other side connected to ground. If the condition I describe is accurate, then the "L" is the obvious dipole element, and the ground is the other, non obvious, dipole element. I bet if you lifted the ground and duplicated the obvious visible "L" with a similar "L" you will get much better reception. The earth is almost always a very poor conductor. Unless you live in a salt marsh, there are many better options. A ground should be viewed as something needed to drain static or energy from a nearby lightning strike, not a active part of the antenna system. When was the last time you had to ground a set of VHF rabbit ears for the antenna to work? I suspect that because radio started before there were widespread man made RF noise sources, and the "L" antenna you describe worked very well even with the poor ground conductivity. In today's noisy world it is seldom the best, or even an acceptable option. And before you ask, yes I have the parts on hand to erect an emergency "L" antenna in the event my nice and fancy active dies and I need to listen in a hurry. Of course I also have a trap dipole that I could erect in a hurry for my ham radio transceiver. I really don't expect any emergencies, but given the ice storms hitting the mid west, you never know. Terry |
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