Hi Frank,
Thanks for your very useful comments. Below my answers: >Radiation results from RF current flowing in an antenna. An RF >ammeter is a useful instrument for measuring the relative efficiency >different types of matching networks feeding similar antennas. Granted. I might want to add that to my plans. I know that the WSPRLite tolerates no more than 100 mW of reflected power, and to avoid accident risk I intend to set the transmit power to no more than 100 mW. I do not know how the units might fold back transmit power in a scenario where the SWR is good but less than perfect. For this reason I am planning to use a tuner whenever SWR is not very close to ideal. The location of the tuner would be wherever it would make sense to place it in field operation. If I add ammeters, they would be placed at the feedpoint, which should work well when I compare different impedance transformers using identical wires. If I compare to non-resonant wires or center feed, it would be hard to compare ammeter readings. > 1. The two antennas under test should be located within less than >one wavelength of each other, otherwise independent selective fading >becomes a significant source of measurement error. Interesting. You are saying that this applies even if the comparison is done over several hours? In my limited back yard, and because I want the feedpoints close to each other, I will certainly meet the requirement of staying withing one wavelength. >2; Horizontally polarized antennas should be oriented end-to-end >to each other to avoid significant parasitic interaction that washes >out the other differences in antenna performance My earlier comments about end-fed antennas focused on vertical wires since the thread originator had tall trees that suggest vertical orientation. My preferred 24” support poles used with 60+ ft wires lead me to the inverted vee configuration which will be horizontally polarized. I am surprised that you can avoid parasitic interaction if you place the wires end-to-end. I was under the impression that end-to-end vertical wires, as in an elevated vertical with a resonant length of vertical feedline under it, with a common mode choke preventing current going from the radiator to the coax shield, would still suffer from parasitic coupling unless an additional common mode choke is added somewhere along the feedline to break up the resonance. I am influenced here by a QST article about vhf/uhf verticals where it seemed that multiple common mode chokes were found necessary to prevent feedline radiation. Anyway, these situations should be easy to model, and I assume you have looked closely at it. I should have enough room to place my inverted vee’s end-to-end if you are sure that is the best way. >3, Do not attempt to compare horizontally polarized antennas to >vertically polarized antennas, independent selective fading >becomes a significant source of measurement error that takes >an extraordinary amount of data collection to overcome. Comparison between horizontal and vertical configuration is not part of my present plans, but I have to admit previously comparing my R5 vertical to my horizontal HF beam. I ran it several hours in several sessions at different times.There were times of day where sometimes the vertical seemed to work better than the beam, although overall the beam looked much better. Do I understand you to say that this comparison was flawed because of insufficient time spent? 73, Erik K7TV >Enjoy! >73 >Frank >W3LPL ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
