Hence, there is no optimum single-fit solution. See the table above. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. (LogOut/ 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. Can I get away with no capacitor in my design? Can a diode be used to rectify signals smaller than its threshold voltage? High self-resonant frequency. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Regards VE9HAM. ROB@COMCOIL.COM Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. That is an end-fed, but very different then the half wave construction. Very interesting design. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. By using traps, the antenna works on all three bands with no operator interaction. 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? 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. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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). Most of the time 5 to 20W will be adequate for activation anyway. I tossed the line as far up as I could in a tree. 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. Refurbishing aluminium antenna parts affected by weather / corrosion. 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. So, how to construct an end-fed half wave antenna? There is lot of controversy around the EFHW antennas. Above, 3t on the primary delivers Gcore<0.002S. 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. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. IIRC they call it a "compensator". It is recommended to use at least 2W non-inductive resistors for this purpose. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. 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 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. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. I particularly want to know how counterpoise affects the common mode currents on the coax. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. 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. 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. If you stare at the above frequency sweeps you will discover a few things. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. These dimensions were derived from modelling the antenna in EZNEC. Research salary, company info, career paths, and top skills for Software Engineer - EDI 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. It is all about getting the heat out. 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. So, I embarked on testing it for myself. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. 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. Make sure the first wire is wrapped evenly around the whole toroid. 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Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. VSWR<1.8 over all of HF. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Looking at several builds and discussions, such as commercial antennas (e.g. Hello, a wonderful approach for the problems.. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. First, note that the transformer has low transmission loss up to nearly 50MHz. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. You can start with the links below. Im very happy with the result. Could it be something to do with the new vertical aerial I had recently installed? My question is what is 'higher frequency' specifically? For . Now I just need to build or acquire a decent radio to utilize this new antenna. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. Why had I not noticed this before? Thank you for your comment and feedback on the article about the EFHW antenna. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 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. Understanding Antennas The Good, the Bad, and the Ugly. In this case, it looks important. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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 was curious why this capacitor was added to the transformer. If not a lightning strike, I will write an article about the experience as well. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. stream Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. The overall lenght is only 15m. I decided to play with this to see what I could accomplish. I will publish my findings, but I cannot not promise to complete it until early fall. It performed well on both the 2m and 70cm bands. Does your station desperately need a good RF ground to behave properly? 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. 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. 100W on a Wire Antenna - How far would it reach? I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. 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. Lowest frequency = 7.000 MHz. 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 finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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. As I reexamined my formula, you pointed it out correctly, there is an error in it. My design objectives were: 1. I will go back and have the article corrected. Most informative and appreciated. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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 model results show the need for a not entirely insignificant counterpoise. 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 mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Im very pleased with that indeed. The SWR for the 20 meter EFHW antenna was < 1.2:1 Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Look at the compensation coil slide. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 2006. This will also be handling 100W. Thank you for an interesting and informative read. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. = 1/30.e6 = 33 nS. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Check your inbox or spam folder to confirm your subscription. 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. P.S. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Jim, do you mind if I add your email and my answer as a comment to the article? This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. of the wavelength. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. 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??). coil inductance calculator at 66pacific.com. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. This can then, fed with coaxial cable, in many cases be . In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. The technical storage or access that is used exclusively for statistical purposes. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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'. There are two aspects, however that we need to consider: Lets begin with the transformer. 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. The latest news about Efhw Compensation Coil Experiment. 100W on a Wire antenna! This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. 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. 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. 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. . Above 7MHz, there is very little temperature dependence at all. This antenna is working for 80,40,20,10 and 6m bands. Zin=46.52+j6.72. Frank VK1VK. Hi Ajai, After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. A radio station is as good or as bad as the antenna it has. 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. It is important to consider the voltages on this tank circuit. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. The highest frequency could be14.350MHz. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. And of course, a counterpoise with various lengths. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Z8Vq9_@x C\Agv#. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. The Counterpoise is a short, typically one twentieth (0.05 *. ) Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. That will be the missing resistor in the resistor bridge of the below circuit. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. The basic question before us is how does an antenna work? The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The results are presented below. I mounted the transformer on a tree for testing. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. I then added two 220pf capacitors in series between the center conductor and ground. 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. On the transformer, I added a few wingnuts to tighten down the antenna wire. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Can you give me an idea for your 100 W version, you built for 80/60/40 m. The 2 coils are 35uh and 90uh. 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. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. This provides proper insulation from the relatively high voltages on the seconder winding.
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