I like to think of an Inverted L as a vertical antenna and a horizontal wire matching device. This is not entirely accurate, but is close enough for contact distances over 2000 miles. An examination of patterns with EZNEC will help you put this into perspective. The vertical portion is the difficult to erect portion of the inverted L and does most of the radiating for DX. The pattern is much like a short vertical for lower frequencies where the vertical length is usually much less than one quarter wave length, but the horizontal portion will raise the radiation resistance from usually single digits to nearer 50 ohms and increase the current in the vertical leg, thus give you more low angle signal. For higher frequencies where antenna vertical lengths greater than one quarter wave and radiation resistance more than 36 ohms or sometimes much less. An inverted L is often a good choice for 160 meters and sometimes 80 meters for those of us who cannot erect a 250 foot vertical to get an optimum low angle signal. A 120 foot vertical is a good compromise and 15 or so ohms of ground resistance is a good counterpoise for a near 50 ohm match, but if that is not doable a 60 foot vertical and a 60 or so foot horizontal leg is a decent antenna with a more reasonable cost. If your operating frequency is higher then the inverted L is attractive only under special circumstances such as emergency, portable or antenna restrictions. Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart
________________________________ From: David Gilbert <xda...@cis-broadband.com> To: elecraft@mailman.qth.net Sent: Tuesday, October 1, 2013 5:09 PM Subject: Re: [Elecraft] Random wires I suggest reading W8JI ... and others. http://www.w8ji.com/radiation_resistance.htm Dave AB7E On 10/1/2013 2:53 PM, k3...@comcast.net wrote: > Sorry roger, Roger, your analysis is not totally correct. You do raise the > feed impedence from 36 Ohms as compared to using a single 1/4 wave wire over > perfect ground. As most of us do not have perfect ground, there is an > imperfect representation of the virtual 1/4. Because it is imperfect, you can > look at this part as absorbing energy and just returning heat. By raising the > radiation impedance, less energy is absorbed by ground and more is radiated. > How much additional efficiency do you obtain is a matter of the ground system > you put in and the ground constants under it. In my experience, it is worth > the effort to build the antenna as it will outperform a similar single wire > inverted L. I suggest reading Bill Orr, and others, on this antenna. > > 73, > Barry > K3NDM > > ----- Original Message ----- > > From: "Roger D Johnson" <n...@roadrunner.com> > To: elecraft@mailman.qth.net > Sent: Tuesday, October 1, 2013 3:40:49 PM > Subject: Re: [Elecraft] Random wires > > This is NOT true! It merely raises the feedpoint impedance...just the same as > adding a > 4-1 transformer. > > 73, Roger > > > On 10/1/2013 3:10 PM, Barry LaZar wrote: >> >> As I read your post, I infer that at the moment you are wanting to add 160 >> meters to your capability. An antenna that I have used and liked is the Twin >> Lead Marconi. It's a simple, cheap, and effective antenna. I first saw it >> written up by Bill Orr years ago. The premise of the design is that a quarter >> wave antenna driven against ground may not be the most efficient antenna due >> to low radiation resistance. Therefore, raise the radiation resistance by >> using the theory of a folded dipole. The folded element raises the radiation >> resistance by a factor of 4 for 2 elements as the impedance changes as the >> square of the number of elements. You will still need radials, but your >> ground >> losses will decrease. >> >> >> 73, >> Barry >> K3NDM >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
