Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF The overlaid VSWR plots are shown below. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. The computation method is also touched on. There is lot of controversy around the EFHW antennas. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. High self-resonant frequency. One end is about 5 meters high on an extended fishing pole. Why had I not noticed this before? Then I covered the coil in kapton tape to hold it together. The antenna is up. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. One possible explanation is that the core losses drop with temperature. I tossed the line as far up as I could in a tree. Im very pleased with that indeed. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. Also find news related to Efhw Compensation Coil Experiment which is trending today. = .000001 / 3868.88 The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The biggest uncertainty in these measurements was the actual power level used. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. I dont have an amplifier, so only need to be able to handle 100W. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. This antenna is only 15m long using 2 loading coils. It requires a set distance to hang both ends of the antenna, and that is not always given. Zin=46.52+j6.72. I first mounted the SO239 connector to the box. And now I am planning to build one for 160/80m. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Above is a sweep of the roughly compensated transformer. In his article, I will try to bust some of the myths associated with Inverted. I found it very useful to label the tuner with switch and capacitance positions. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. (Tvir s tvbeszl gpek s kszlkek) Ksznm. See the second completed tuner depicted below. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. And not all hf antenna installation are same, with most requiring bit of tinkering. If you really want to get the heat out, add some fins to the aluminum box. blue: 250pF, to much compensation. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. A radio station is as good or as bad as the antenna it has. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. ROB@COMCOIL.COM The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. The overall lenght is only 15m. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. I can give a link if you need. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). Start by wrapping the wire around the toroid. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. If you stare at the above frequency sweeps you will discover a few things. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. The equation should have a 10^6 and not 10^-6 in the nominator. 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 made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. What kind of balun is this? stream Looking at several builds and discussions, such as commercial antennas (e.g. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. The results are shown below. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Lowest frequency = 7.000 MHz. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. 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" The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. Impressive article and so well done that I may give it a try. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. It is worth experimenting with its length also. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 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. Instead, this shifts everything down and makes it very easy to tune 10m. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change.