efhw compensation coil10 marca 2023
How big and where to place it is likely best determined empirically. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. And now I am planning to build one for 160/80m. Trapped five band EFHW SOTA antenna. The basic question before us is how does an antenna work? 2. (LogOut/ (LogOut/ However, a key restriction is its 25W power rating, due to the small matching transformer. I checked the wall brackets and mast, but all the fixings were nice and tight. 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 will publish my findings, but I cannot not promise to complete it until early fall. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. So far so good. The SWR was measured for each of the three antennas across the CW portion of the bands. 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. Start by wrapping the wire around the toroid. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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). % The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. 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. There are two aspects, however that we need to consider: Lets begin with the transformer. We use cookies to optimize our website and our service. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. I wish you lots of productive experimentations and successful portable operations. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. It will present its parameters, so anybody with basic home-brew skills will be able to build it. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 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. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Above is a sweep of the roughly compensated transformer. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. The technical storage or access that is used exclusively for statistical purposes. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. This antenna is working for 80,40,20,10 and 6m bands. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. of the wavelength. 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. High Q, hence low loss. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. The final turns ratio turned out to be 3:29. Highest frequency = 14.350 MHz. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? Thank you for an interesting and informative read. The SWR figures were as follows: FT240-43 132ft/100pF capacitor One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. 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 2 coils are 35uh and 90uh. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Lets do a quick calculation to see how much an issue is this output capacitance. Lowest measured inductivity = 2.0 H. 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. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Be sure to take a look for additional analysis and conclusions. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Most informative and appreciated. 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. I am currently working on measurements of an EFHW antenna. The band compensating inductor placed on the wire is another story. The parasitic reactances near the feed-point also vary between installations. I wish I had a simple answer, but really this is where some experimentation can pay off. |k"^N>F.AnJkJsq'PV}o0I. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). However, it has its idiosyncrasies. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. Transmitting on 15 meters was impossible because of RF into the radio. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. View the job description, responsibilities and qualifications for this position. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 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'. Csatlakozz csapatunkhoz! IIRC they call it a "compensator". I used four parallel #28 wires (not twisted) for the primary. = .00 00 00 00 0 258 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Workers' Comp. 73! ROB@COMCOIL.COM 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. Can I get away with no capacitor in my design? Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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. 73 Firstly, bandwidth on 80m is restricted to about 80 kHz at . 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. How to get started on ISS Cross band Repeater? Nagyon j ez a cikk. 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. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. I decided to play with this to see what I could accomplish. 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. If you stare at the above frequency sweeps you will discover a few things. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. 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. 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 mounted the transformer on a tree for testing. It not a loading coil. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Could it be something to do with the new vertical aerial I had recently installed? Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 100W on a Wire Antenna - How far would it reach? Note: If we change the primary number of turns, the impedance ratios will considerable change also. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. A 100pF silvered mica was connected in shunt with the transformer . 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. 2015. It is worth experimenting with its length also. The toroid with its many taps may be soldered directly on a multi-position switch. 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. I am planning to use this latest one at the Field Day next year. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! No capacitor was installed. Above is a thermograph of the transformer at 20W input at 3.6MHz. = 1/30.e6 = 33 nS. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Klubunknl folyamatos a tagfelvtel. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Interpretation of S-Meter Noise Floor in HF Radio Receivers. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. The worse SWR was 1:1.7 at the top end of 20 meters. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. A ktelez mezket * karakterrel jelltk. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. Apply for the Job in Software Engineer - EDI at St. Louis, MO. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! The negative effects of local QRM on an, How does antenna radiation occur? The original coil is designed for low power portable applications. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Not the ideal antenna, but convenient! The equation in the article is corrected now. The previous table already contains these measurements. For a quarter wave that is about 8 nS. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. The results are presented below. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Impressive article and so well done that I may give it a try. 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. It is not necessary to calculate the above; the results are sown in the following table. 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. %PDF-1.4 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. More designs can be found by Googling "80m loaded dipole.". 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 overall lenght is only 15m. . 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. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. I assume you know the GNARC source for EFHW antennas. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 1. Some say you do not need a counterpoise, but that is false. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Taking the time derivative of the above equation you get the power dissipation. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Low SSN Why do most Hams find HF Radio so difficult? 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. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Looking at several builds and discussions, such as commercial antennas (e.g. 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. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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. I needed to add an additional coil (approx 12.5 uH) about . To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. To further improve the flux linkage, I wound the primary on top of the secondary. But systems that work better increase the prospects of contacts. Frank VK1VK. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. This antenna is only 15m long using 2 loading coils. The cooling curve I measured is shown below. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. It is important to consider the voltages on this tank circuit. We need to measure the inductances of the toroid with the tapped coil. Change), You are commenting using your Facebook account. . So, I embarked on testing it for myself. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. I found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. 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 real power limit will be core heating. 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. How does this SWR meter works? The latest news about Efhw Compensation Coil Experiment. This suggests an inductive reactance. It should be no surprise that 80pF is close to optimal. nanoVNA-H can firmware be updated if it has a broken USB socket? The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. One point of my small-core, compact winding design was to be able to cool the core. From that we can find Mismatch Loss. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). This can then, fed with coaxial cable, in many cases be . 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. VK1OD.net (offline). After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. See the table above. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line.
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