The antenna is effective and the materials and construction are of a very high quality. Trapped five band EFHW SOTA antenna. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. I wish I had a simple answer, but really this is where some experimentation can pay off. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Workers' Comp. 100W on a Wire antenna! This will yield the minimal capacitance of the variable capacitor. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. Be aware counterpoise or ground radials are required for all hf antennas for better performance. The technical storage or access that is used exclusively for statistical purposes. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Lowest frequency = 7.000 MHz. Transmitting on 15 meters was impossible because of RF into the radio. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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.) There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. The SWR figures were as follows: FT240-43 132ft/100pF capacitor A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. Efhw Compensation Coil Experiment - Local Search Denver Post I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. The latest news about Efhw Compensation Coil Experiment. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. 2006. = .00 00 00 00 0 258 The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Looking at several builds and discussions, such as commercial antennas (e.g. From that we can find Mismatch Loss. VSWR<1.8 over all of HF. 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. This suggests an inductive reactance. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Hence, there is no optimum single-fit solution. 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. I installed a QRP SWR meter into the tuner that makes tuning very handy. Your posting put it all together for meTHANK YOU!!!! 100W on a Wire Antenna How far would it reach? Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. High self-resonant frequency. I found it very useful to label the tuner with switch and capacitance positions. Well, in ham radio, everything works. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Thanks for your comments. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. 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). 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. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The resistance (real) component of the impedance is right where we want it near 50 ohms. Thank you for an interesting and informative read. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. The parasitic reactances near the feed-point also vary between installations. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. = .000001 / 3868.88 The EFHW transformer box from outside. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Could it be something to do with the new vertical aerial I had recently installed? 73 Research salary, company info, career paths, and top skills for Software Engineer - EDI If you stare at the above frequency sweeps you will discover a few things. Looking at several builds and discussions, such as commercial antennas (e.g. The negative effects of local QRM on an, How does antenna radiation occur? Highest frequency = 14.350 MHz. Ismerje meg a hozzszls adatainak feldolgozst . 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. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? The SWR for the 20 meter EFHW antenna was < 1.2:1 Experiments with 160m antennas | VK3IL Blog A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 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. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Many people use an inductor placed at the near end to make things level out on the higher bands. The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. It depends on the selection of the inductance and the capacitor values. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . The patterns fro the horizontal wire is compared with those of an inverted-V configuration. You cant really see the antenna wire, but the red line shows the antenna path. Understanding Antennas The Good, the Bad, and the Ugly. My End-Fed Half-Wave (EFHW) AmateurRadio.com 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. Below about 7 MHz, transmission losses increase as the core temperature increases. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. The biggest uncertainty in these measurements was the actual power level used. Taking the time derivative of the above equation you get the power dissipation. View the job description, responsibilities and qualifications for this position. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. 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). For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. The results are presented below. 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. Current Balun 1. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Two layers of 1mil Kapton tape are placed over the winding. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite The equation should have a 10^6 and not 10^-6 in the nominator. 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. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. 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. I am building an EFHW antenna for my new. Pocket-tenna core is finally done! Wire and compensation coil being After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. This can then, fed with coaxial cable, in many cases be . Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Make sure the first wire is wrapped evenly around the whole toroid. 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. Isn't it? I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. . However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. I am planning to use this latest one at the Field Day next year. EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com Wrap the first wire around the toroid 27 times (I used a black wire for this). You can see the coil in the picture below (red arrow). For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. I used the 14g enameled wire and wound it on the FT240-43. So I built myself an improved replacement matching 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. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . . I would mention first its ease of installation. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. 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. coil inductance calculator at 66pacific.com. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Most of the time 5 to 20W will be adequate for activation anyway. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. Nagyon j ez a cikk. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Is FT8 popularity growing at the cost of SSB Phone and CW? I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. I used four parallel #28 wires (not twisted) for the primary. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. I ran WSPR at 10mW for about 2 hours and got the results below. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. Not the ideal antenna, but convenient! The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Copyright 2014-2023. Jim, do you mind if I add your email and my answer as a comment to the article? 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. 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. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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 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. Will there be the same performance for single band EFHWs? The SWR results are as follows: The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. 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. blue: 250pF, to much compensation. There are two aspects, however that we need to consider: Lets begin with the transformer. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The overlaid VSWR plots are shown below. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. As is often the case, packaging was determined by what boxes I had laying around. That is an end-fed, but very different then the half wave construction. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency Lets call this element the LoadAttenuator. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. I added some Christmas colored zip ties to hold everything in place. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. They will be adjusted for resonance at or close to the CW portion of the bands. A short 80m antenna for my lot - KB6NU's Ham Radio Blog I mounted the transformer on a tree for testing. I checked the wall brackets and mast, but all the fixings were nice and tight. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. It performed well on both the 2m and 70cm bands. 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. 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. A week or two later I started to notice an occasional knocking sound inside the house. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube 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. What are the advantages and disadvantages of the end-fed half wave antenna? However, a key restriction is its 25W power rating, due to the small matching transformer. 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. 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. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. I decided to push for best efficiency with a 5-turn primary. 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. Zin=46.52+j6.72. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. I assume you know the GNARC source for EFHW antennas. 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. = 1/30.e6 = 33 nS. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. Can I get away with no capacitor in my design? Now I just need to build or acquire a decent radio to utilize this new antenna. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The basic question before us is how does an antenna work? 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio The worse SWR was 1:1.7 at the top end of 20 meters. With such a switch, it is impossible to forget to switch back to operational mode. application of Kirchhoff's current Law on a typical EFHW antenna configuration.