Some website features may not function optimally without cookies. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. The bridge than will measure zero voltage across the bridge, and the LED will turn off. 2 0 obj Above 7MHz, there is very little temperature dependence at all. 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. I installed a QRP SWR meter into the tuner that makes tuning very handy. Im very pleased with that indeed. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Thirty turns #28 are wound on the two FT114-43 cores. This gave me an effective coil diameter of 40.5mm. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! This can then, fed with coaxial cable, in many cases be . This will yield the maximum capacity of the variable capacitor. This will also be handling 100W. Thanks in advance, good health for you in these times, Looking at several builds and discussions, such as commercial antennas (e.g. Klubunknl folyamatos a tagfelvtel. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. In an urban area we are much more restricted, especially if we need to be stealth about it. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. 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. The SWR for the 20 meter EFHW antenna was < 1.2:1 Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. The toroid with its many taps may be soldered directly on a multi-position switch. The basic question before us is how does an antenna work? A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It not a loading coil. 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. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. For a quarter wave that is about 8 nS. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. Below is the schematic of the final build. Also find news related to Efhw Compensation Coil Experiment which is trending today. Let me review the salient observations from the previous work. I mounted the transformer on a tree for testing. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. No wire counterpoise is used to reproduce the SOTA setup. Zin=46.52+j6.72. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. 100W on a Wire antenna! It is all about getting the heat out. 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. 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. A week or two later I started to notice an occasional knocking sound inside the house. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Some say you do not need a counterpoise, but that is false. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Refurbishing aluminium antenna parts affected by weather / corrosion. The resistance (real) component of the impedance is right where we want it near 50 ohms. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. By using traps, the antenna works on all three bands with no operator interaction. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. A 100pF silvered mica was connected in shunt with the transformer primary. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. They will be adjusted for resonance at or close to the CW portion of the bands. It is worth experimenting with its length also. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. It is not necessary to calculate the above; the results are sown in the following table. 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Frank VK1VK. I can give a link if you need. We do not know what the actual impedance will be at the end of the antenna radiator. Many people use an inductor placed at the near end to make things level out on the higher bands. The band compensating inductor placed on the wire is another story. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Basically, the loading coil is operating as a trap. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. I then used a piece of heat shrink on the outside to hold everything in place. This will yield the minimal capacitance of the variable capacitor. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. Current Balun 1. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. The worse SWR was 1:1.7 at the top end of 20 meters. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. The next important parameter is the parallel resonant circuits resonant frequency. Below about 7 MHz, transmission losses increase as the core temperature increases. It performed well on both the 2m and 70cm bands. 73 When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. It is worth experimenting with its length also. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. blue: 250pF, to much compensation. There is much more that can be written about this antenna and its matching, but that was not my aim. See the table above. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. Impressive article and so well done that I may give it a try. Csatlakozz csapatunkhoz! From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. 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. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Change), You are commenting using your Facebook account. Is FT8 popularity growing at the cost of SSB Phone and CW? It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. The combination of the transformer with the end-fed dipole results in a positive reactance. 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. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Start by wrapping the wire around the toroid. Im very happy with the result. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The final turns ratio turned out to be 3:29. How big and where to place it is likely best determined empirically. 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. Cmzett: Weince joseph How can we help? The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Z8Vq9_@x C\Agv#. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Can a diode be used to rectify signals smaller than its threshold voltage? However, I think I made a good choice with a Hammond 1590A diecast aluminum box. stream = .000001 / 3868.88 Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. So the differences I see in the data sheets hysteresis curves are not the correct explanation. It is recommended to use at least 2W non-inductive resistors for this purpose. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. This provides proper insulation from the relatively high voltages on the seconder winding. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. Research salary, company info, career paths, and top skills for Software Engineer - EDI This graphical depiction makes it easier to visualize the current and impedance correlation between bands. But systems that work better increase the prospects of contacts. Hello, a wonderful approach for the problems.. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I found it very useful to label the tuner with switch and capacitance positions. The parasitic reactances near the feed-point also vary between installations. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. On the transformer, I added a few wingnuts to tighten down the antenna wire. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 5) It is very hard to avoid stray capacitance on the output. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. The original coil is designed for low power portable applications. I assume you know the GNARC source for EFHW antennas. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. 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. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). The overlaid VSWR plots are shown below. And of course, a counterpoise with various lengths. VK1OD.net (offline). Trapped five band EFHW SOTA antenna. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Thank you for your comment and feedback on the article about the EFHW antenna. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. I decided to play with this to see what I could accomplish. Lets call this element the LoadAttenuator. That will be the missing resistor in the resistor bridge of the below circuit. This is typically a weak spot. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look.
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