efhw compensation coil

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. Klubunknl folyamatos a tagfelvtel. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. 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. 73! So the differences I see in the data sheets hysteresis curves are not the correct explanation. In his article, I will try to bust some of the myths associated with Inverted. 73 In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. There are many good descriptions on the net about this type of antenna. It is best to make the impedance matching adjustable, using switched transformation ratio. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. Ismerje meg a hozzszls adatainak feldolgozst . I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. One possible explanation is that the core losses drop with temperature. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. More designs can be found by Googling "80m loaded dipole.". It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. I use shock cord to connect the insulator at the end of the wire to my fence. 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. Above 7MHz, there is very little temperature dependence at all. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. Which begs the question what happens when you attach the antenna? 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. And of course, a counterpoise with various lengths. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. I particularly want to know how counterpoise affects the common mode currents on the coax. It may be one or even five kilo-ohms. Can a diode be used to rectify signals smaller than its threshold voltage? In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Let me review the salient observations from the previous work. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Copyright 2014-2023. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. 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. Finally the tank circuits specification is complete, which is sown below. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. That is an end-fed, but very different then the half wave construction. Understanding Antennas The Good, the Bad, and the Ugly. The final turns ratio turned out to be 3:29. Cmzett: Weince joseph How can we help? One way or another there is always a counterpoise involved if the antenna is tuned correctly. VK1OD.net (offline). The final turns ratio turned out to be 3:29. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. % An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Best regards and thanks again for your comment. This will yield the maximum capacity of the variable capacitor. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. Jos van den Helm's (PA1ZP) article published in Radcom: Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. ROB@COMCOIL.COM Instead, this shifts everything down and makes it very easy to tune 10m. However, a key restriction is its 25W power rating, due to the small matching transformer. It performed well on both the 2m and 70cm bands. The equation in the article is corrected now. My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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 toroid with its many taps may be soldered directly on a multi-position switch. You cant really see the antenna wire, but the red line shows the antenna path. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I needed to add an additional coil (approx 12.5 uH) about . These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. This will also be handling 100W. High self-resonant frequency. Zin=46.52+j6.72. It uses a coil as a compensation unit, and no counterpoise. What are its disadvantages? Is it any good? I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. I decided to play with this to see what I could accomplish. All Rights Reserved. Will there be the same performance for single band EFHWs? This gave me an effective coil diameter of 40.5mm. Lowest frequency = 7.000 MHz. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Even at 15W the voltage at the ends may reach 100-200V. I ran WSPR at 10mW for about 2 hours and got the results below. Thanks for your comments. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. 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. I look at the end-fed as just an extreme example of an off-center-fed antenna. It should be no surprise that 80pF is close to optimal. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Hence, there is no optimum single-fit solution. I wish you lots of productive experimentations and successful portable operations. The worse SWR was 1:1.7 at the top end of 20 meters. of the wavelength. I checked the wall brackets and mast, but all the fixings were nice and tight. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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'. 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. Be cautious, such voltages may cause a quite painful skin scorch. Elnzst krnk, de elsikkadt az zenete. And not all hf antenna installation are same, with most requiring bit of tinkering. 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" You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. The wire as I strung it up seemed to resist having a good SWR for the 20m band. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Check your inbox or spam folder to confirm your subscription. Im very happy with the result. 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. Subscribe to our newsletter and receive regular updates on new posts and articles. It is all about getting the heat out. Z8Vq9_@x C\Agv#. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Above is a sweep of the roughly compensated transformer. 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 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. Make sure the first wire is wrapped evenly around the whole toroid. 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. 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). That will be the missing resistor in the resistor bridge of the below circuit. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Refurbishing aluminium antenna parts affected by weather / corrosion. stream I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. = .00 00 00 00 0 258 There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Many people use an inductor placed at the near end to make things level out on the higher bands. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 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. This is perhaps one of the most hotly debated rookie topics in. Look at the compensation coil slide. Well, in ham radio, everything works. 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. They will be adjusted for resonance at or close to the CW portion of the bands. See the second completed tuner depicted below. If you stare at the above frequency sweeps you will discover a few things. Basu Bhattacharya (VU2NSB). This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. 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. This provides proper insulation from the relatively high voltages on the seconder winding. Do I count the six loops around the pvc in the measurement? From that we can find Mismatch Loss. For a quarter wave that is about 8 nS. A radio station is as good or as bad as the antenna it has. You can see the coil in the picture below (red arrow). Im very pleased with that indeed. = 258 * 10^-12. 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. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. The parasitic reactances near the feed-point also vary between installations. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? It does not need any special components; in fact, most of us may have them in our shack drawers already. It will present its parameters, so anybody with basic home-brew skills will be able to build it. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. It requires a set distance to hang both ends of the antenna, and that is not always given. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. The previous table already contains these measurements. This is typically a weak spot. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. I then used a piece of heat shrink on the outside to hold everything in place. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. How far could it possibly reach? Regards VE9HAM. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. The impedance matching circuit is essentially a simple parallel resonant LC circuit. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. We need to measure the inductances of the toroid with the tapped coil. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. And now I am planning to build one for 160/80m. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Research salary, company info, career paths, and top skills for Software Engineer - EDI It not a loading coil. This is not an optimal value, benefit may be obtained by exploring small changes to that value. nanoVNA-H can firmware be updated if it has a broken USB socket? See the table above. 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. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. The combination of the transformer with the end-fed dipole results in a positive reactance. 1. I used four parallel #28 wires (not twisted) for the primary. 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. I found it very useful to label the tuner with switch and capacitance positions. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. We use cookies to optimize our website and our service. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Could it be something to do with the new vertical aerial I had recently installed? The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 2 0 obj . Basically, the loading coil is operating as a trap. Krem, rja le, mi a krdse. I would mention first its ease of installation. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. VSWR<1.8 over all of HF. Your article was well written and very informative, thanks. Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. 2. Can you give me an idea for your 100 W version, you built for 80/60/40 m. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Let us touch on some necessary theory to begin with. What kind of balun is this? High Q, hence low loss. Impressive article and so well done that I may give it a try. How does this SWR meter works? I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. However, a key restriction is its 25W power rating, due to the small matching transformer. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The antenna is up. Compensation. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. No capacitor was installed. 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. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. The antenna is effective and the materials and construction are of a very high quality. To further improve the flux linkage, I wound the primary on top of the secondary. The SWR results are as follows: The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Not the ideal antenna, but convenient! Trapped five band EFHW SOTA antenna. Consequently, this is how the capacitance values are determined. 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. It is worth experimenting with its length also. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. 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 record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. As is often the case, packaging was determined by what boxes I had laying around. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. The highest voltages as well as radiation are also at the end of the antenna wire. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Why had I not noticed this before? Why does antenna radiation occur? Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. The highest frequency could be14.350MHz. The Counterpoise is a short, typically one twentieth (0.05 *. ) 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. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. 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. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 100W on a Wire Antenna - Is it good enough for DX? The technical storage or access that is used exclusively for anonymous statistical purposes. Note: If we change the primary number of turns, the impedance ratios will considerable change also. The basic question before us is how does an antenna work? 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. Also find news related to Efhw Compensation Coil Experiment which is trending today. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces.

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