efhw compensation coil

I wish I had a simple answer, but really this is where some experimentation can pay off. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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 Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. We use cookies to optimize our website and our service. Cmzett: Weince joseph How can we help? Thanks for your comments. I am building an EFHW antenna for my new. It may be one or even five kilo-ohms. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. 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%. Compensation. Below is the schematic of the final build. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. I will publish my findings, but I cannot not promise to complete it until early fall. 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. 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. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Thank you for an interesting and informative read. 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. Not the ideal antenna, but convenient! 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. Your article was well written and very informative, thanks. The latest news about Efhw Compensation Coil Experiment. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. i liked it a lot, you give good ideas, many thanks. 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. Then I covered the coil in kapton tape to hold it together. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. It is worth experimenting with its length also. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. You can start with the links below. The wire as I strung it up seemed to resist having a good SWR for the 20m band. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. I checked the wall brackets and mast, but all the fixings were nice and tight. We also need to know what are the frequencies or bands for which we plant to use this antenna. In this case, it looks important. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Next, I started winding the transformer. In theory, the examination is supposed to be used to help clarify your medical condition and . The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering The cooling curve I measured is shown below. I use shock cord to connect the insulator at the end of the wire to my fence. 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. The real power limit will be core heating. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Interpretation of S-Meter Noise Floor in HF Radio Receivers. 100W on a Wire Antenna - How far would it reach? 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.) The 2 coils are 35uh and 90uh. 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. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. A Smith chart view of EFHW transformer compensation End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. A 100pF silvered mica was connected in shunt with the transformer . This is typically a weak spot. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. For the last step, I put together a RF choke to use between the radio and the feedline. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Z8Vq9_@x C\Agv#. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. end fed half wave antenna - awsh.org The EFHW transformer box from outside. 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). 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 also will ask, why didnt it work for you. uBITX HF Transceiver Build - My Adventures in Engineering From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Highest frequency = 14.350 MHz. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I can give a link if you need. At this point, I'm leaning towards the EFHW, but any of these antennas seem . I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. It is important to consider the voltages on this tank circuit. Nagyon j ez a cikk. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. 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. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. The original coil is designed for low power portable applications. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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" Thirty turns #28 are wound on the two FT114-43 cores. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. To be safe, better not get much above 120 C. clear. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. A week or two later I started to notice an occasional knocking sound inside the house. |k"^N>F.AnJkJsq'PV}o0I. Graphed with a log scale, it makes a nice straight line. (Tvir s tvbeszl gpek s kszlkek) Ksznm. 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. = 258 * 10^-12. 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. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. 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. This reveals we only need to compensate for the reactive component. Thanks again Jim. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. 73 Regards VE9HAM. For a quarter wave that is about 8 nS. The highest voltages as well as radiation are also at the end of the antenna wire. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net Efhw Compensation Coil Experiment - Local Search Denver Post After some internet research, I settled on making the former from a paint roller. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. 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. Isn't it? EFHW 80m extension - MI0KXX 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 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. PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m 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. 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. % The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. It performed well on both the 2m and 70cm bands. of the wavelength. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The highest frequency could be14.350MHz. 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. 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. One possible explanation is that the core losses drop with temperature. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Do I count the six loops around the pvc in the measurement? The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Hence, there is no optimum single-fit solution. 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 negative effects of local QRM on an, How does antenna radiation occur? Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. 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. And not all hf antenna installation are same, with most requiring bit of tinkering. 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. 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. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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'. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. The overlaid VSWR plots are shown below. If you stare at the above frequency sweeps you will discover a few things. The 40-10m EFHW camping antenna is late but done. More info in - reddit I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. One way or another there is always a counterpoise involved if the antenna is tuned correctly. It not a loading coil. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. How big and where to place it is likely best determined empirically. Is it any good? 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. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. Be sure to take a look for additional analysis and conclusions. First, note that the transformer has low transmission loss up to nearly 50MHz. Proudly created withWix.com. There are many good descriptions on the net about this type of antenna. The difference here is that the target bands are low frequency. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. Change). Make sure the first wire is wrapped evenly around the whole toroid. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. Two layers of 1mil Kapton tape are placed over the winding. Let's find out! I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Apply for the Job in Software Engineer - EDI at St. Louis, MO. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Subscribe to our newsletter and receive regular updates on new posts and articles. 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. Lowest frequency = 7.000 MHz. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The computation method is also touched on. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 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. 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. This will yield the minimal capacitance of the variable capacitor. Lets do a quick calculation to see how much an issue is this output capacitance. Independent Medical Evaluation - IME | Cynthia Hennessey Contact Commercial Coils P.S. I particularly want to know how counterpoise affects the common mode currents on the coax. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Pocket-tenna core is finally done! Wire and compensation coil being Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. Thank you for your comment and feedback on the article about the EFHW antenna. Look at the compensation coil slide. 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. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. I am currently working on measurements of an EFHW antenna. 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. 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. High self-resonant frequency. But I would caution its usage for higher power than 10-15W. Above, 3t on the primary delivers Gcore<0.002S. 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. With no counterpoise wire it will be the coaxs shield providing it. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance.

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