End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. The overall lenght is only 15m. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Thank you for an interesting and informative read. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. ROB@COMCOIL.COM The antennas are set up as a sloper as in my SOTA outings. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! We use cookies to optimize our website and our service. My favorite SOTA antenna is the End-Fed Half Wave Antenna. But I would caution its usage for higher power than 10-15W. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Just the bare 80m wire is shown in red. i liked it a lot, you give good ideas, many thanks. Even at 15W the voltage at the ends may reach 100-200V. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Z8Vq9_@x C\Agv#. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. In theory, the examination is supposed to be used to help clarify your medical condition and . On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). I am building an EFHW antenna for my new. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. We need to measure the inductances of the toroid with the tapped coil. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Nagyon j ez a cikk. I found it very useful to label the tuner with switch and capacitance positions. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 2006. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. The photos above show a method that works fairly well. I was curious why this capacitor was added to the transformer. Lowest frequency = 7.000 MHz. All Rights Reserved. |k"^N>F.AnJkJsq'PV}o0I. Compensation. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. The SWR figures were as follows: FT240-43 132ft/100pF capacitor I used the 14g enameled wire and wound it on the FT240-43. Ismerje meg a hozzszls adatainak feldolgozst . Apply for the Job in Software Engineer - EDI at St. Louis, MO. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Will there be the same performance for single band EFHWs? It is all about getting the heat out. I settled on a compact secondary using #28 wire. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. As I reexamined my formula, you pointed it out correctly, there is an error in it. This provides proper insulation from the relatively high voltages on the seconder winding. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. The antenna is up. It does not need any special components; in fact, most of us may have them in our shack drawers already. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 2015. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Basically, the loading coil is operating as a trap. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. I needed to add an additional coil (approx 12.5 uH) about . I am currently working on measurements of an EFHW antenna. The antenna is effective and the materials and construction are of a very high quality. Although the original loading coil is very well engineered, I thought I could make a more efficient version given that I did not need to make it 'trail friendly'. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. I dont have an amplifier, so only need to be able to handle 100W. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. Hence, we need to move along and start to include the antenna with our testing. One point of my small-core, compact winding design was to be able to cool the core. We do not know what the actual impedance will be at the end of the antenna radiator. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. Cmzett: Weince joseph How can we help? I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. = .000001 / 3868.88 We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. I first mounted the SO239 connector to the box. Could it be something to do with the new vertical aerial I had recently installed? This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The latest news about Efhw Compensation Coil Experiment. I then added two 220pf capacitors in series between the center conductor and ground. To be safe, better not get much above 120 C. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It may be one or even five kilo-ohms. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands.
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