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. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. I ran WSPR at 10mW for about 2 hours and got the results below. The equation should have a 10^6 and not 10^-6 in the nominator. 100W on a Wire Antenna - How far would it reach? I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. Then I covered the coil in kapton tape to hold it together. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. Even at 15W the voltage at the ends may reach 100-200V. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. Ismerje meg a hozzszls adatainak feldolgozst . Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Cmzett: Weince joseph How can we help? However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! We use cookies to optimize our website and our service. Some hams swear by them, yet some completely demean it. 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. Let us touch on some necessary theory to begin with. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Lowest frequency = 7.000 MHz. 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 conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. This antenna is only 15m long using 2 loading coils. Note: If we change the primary number of turns, the impedance ratios will considerable change also. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I found it very useful to label the tuner with switch and capacitance positions. Zin=46.52+j6.72. Copyright 2014-2023. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. It will present its parameters, so anybody with basic home-brew skills will be able to build it. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. I used four parallel #28 wires (not twisted) for the primary. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. If you really want to get the heat out, add some fins to the aluminum box. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. 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. 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. Lets call this element the LoadAttenuator. These dimensions were derived from modelling the antenna in EZNEC. Look at the compensation coil slide. And not all hf antenna installation are same, with most requiring bit of tinkering. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. I needed to add an additional coil (approx 12.5 uH) about . I used the 14g enameled wire and wound it on the FT240-43. For . of the wavelength. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. This gave me an effective coil diameter of 40.5mm. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. It is not necessary to calculate the above; the results are sown in the following table. The technical storage or access that is used exclusively for anonymous statistical purposes. My design objectives were: 1. Which begs the question what happens when you attach the antenna? 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). document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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With such a switch, it is impossible to forget to switch back to operational mode. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 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. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. No wire counterpoise is used to reproduce the SOTA setup. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. 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. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. Two layers of 1mil Kapton tape are placed over the winding. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. Hello, a wonderful approach for the problems.. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Just the bare 80m wire is shown in red. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. How far could it possibly reach? Is it any good? It should be no surprise that 80pF is close to optimal. 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. This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. In theory, the examination is supposed to be used to help clarify your medical condition and . Also find news related to Efhw Compensation Coil Experiment which is trending today. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The biggest uncertainty in these measurements was the actual power level used. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. So far so good. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. It is important to consider the voltages on this tank circuit. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. In this case, it looks important. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. I decided to play with this to see what I could accomplish. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. 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 coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I particularly want to know how counterpoise affects the common mode currents on the coax. 3) Total losses are approximately independent of core volume. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. The photos above show a method that works fairly well. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. This is perhaps one of the most hotly debated rookie topics in. 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 antenna is effective and the materials and construction are of a very high quality. There is lot of controversy around the EFHW antennas. However, the insertion loss of the packaged transformer would be intolerable on the 10 meter band if it appeared the same way with an antenna wire connected. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. A radio station is as good or as bad as the antenna it has. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 100W on a Wire Antenna - Is it good enough for DX? 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. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Be cautious, such voltages may cause a quite painful skin scorch. The technical storage or access that is used exclusively for statistical purposes. Refurbishing aluminium antenna parts affected by weather / corrosion. For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. One end is about 5 meters high on an extended fishing pole. 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. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. . However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. Lowest measured inductivity = 2.0 H. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. I settled on a compact secondary using #28 wire. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. Change). The bridge than will measure zero voltage across the bridge, and the LED will turn off. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. See the second completed tuner depicted below. Consequently, this is how the capacitance values are determined. I also will ask, why didnt it work for you. That will be the missing resistor in the resistor bridge of the below circuit. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Make sure the first wire is wrapped evenly around the whole toroid. Although it is simple to build and is a multiband antenna, it has several attributes that . On the transformer, I added a few wingnuts to tighten down the antenna wire. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 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'.