The equation should have a 10^6 and not 10^-6 in the nominator. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. 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 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. 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 tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 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 . 100W on a Wire Antenna - Is it good enough for DX? The overlaid VSWR plots are shown below. 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 antenna wire could also be tuned for the lower end of 80 meters without the coil but the . A 100pF silvered mica was connected in shunt with the transformer primary. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. If not a lightning strike, I will write an article about the experience as well. I decided to play with this to see what I could accomplish. Some hams swear by them, yet some completely demean it. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. i liked it a lot, you give good ideas, many thanks. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. I am planning to use this latest one at the Field Day next year. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. First, note that the transformer has low transmission loss up to nearly 50MHz. One end is about 5 meters high on an extended fishing pole. Z8Vq9_@x C\Agv#. 2 0 obj Thirty turns #28 are wound on the two FT114-43 cores. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 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. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. 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??). The impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. To be safe, better not get much above 120 C. Lowest frequency = 7.000 MHz. 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. For a quarter wave that is about 8 nS. I am currently working on measurements of an EFHW antenna. More designs can be found by Googling "80m loaded dipole.". 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. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. I am building an EFHW antenna for my new. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Firstly, bandwidth on 80m is restricted to about 80 kHz at . The next important parameter is the parallel resonant circuits resonant frequency. Apply for the Job in Software Engineer - EDI at St. Louis, MO. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Looking at several builds and discussions, such as commercial antennas (e.g. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Which begs the question what happens when you attach the antenna? 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. One point of my small-core, compact winding design was to be able to cool the core. Be aware counterpoise or ground radials are required for all hf antennas for better performance. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 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. 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. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The SWR figures were as follows: FT240-43 132ft/100pF capacitor On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. 73! Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The original coil is designed for low power portable applications. Show more. Csatlakozz csapatunkhoz! I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! High self-resonant frequency. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. This will yield the maximum capacity of the variable capacitor. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. We need to measure the inductances of the toroid with the tapped coil. Compensation. It will present its parameters, so anybody with basic home-brew skills will be able to build it. You cant really see the antenna wire, but the red line shows the antenna path. 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. 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. Im very happy with the result. If you stare at the above frequency sweeps you will discover a few things. I was curious why this capacitor was added to the transformer. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. . Look at the compensation coil slide. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. A week or two later I started to notice an occasional knocking sound inside the house. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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. 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. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. For the last step, I put together a RF choke to use between the radio and the feedline. The difference here is that the target bands are low frequency. Low SSN Why do most Hams find HF Radio so difficult? The SWR was measured for each of the three antennas across the CW portion of the bands. 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. 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. The worse SWR was 1:1.7 at the top end of 20 meters. This is typically a weak spot. Be sure to take a look for additional analysis and conclusions. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. You can see the coil in the picture below (red arrow). The transformer fits sideways in the box with a few millimeters to spare. Also find news related to Efhw Compensation Coil Experiment which is trending today. I mounted the transformer on a tree for testing. Frank VK1VK. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Current Balun 1. However, a key restriction is its 25W power rating, due to the small matching transformer. The final turns ratio turned out to be 3:29. 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. It not a loading coil. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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. Why had I not noticed this before? How far could it possibly reach? Consequently, this is how the capacitance values are determined. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. A 100pF silvered mica was connected in shunt with the transformer . 100W on a Wire antenna! See the second completed tuner depicted below. 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. Your posting put it all together for meTHANK YOU!!!! 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. nanoVNA-H can firmware be updated if it has a broken USB socket? Let me review the salient observations from the previous work. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. I can give a link if you need. 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. With no counterpoise wire it will be the coaxs shield providing it. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. This reveals we only need to compensate for the reactive component. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The original coil is designed for low power portable applications. Thanks in advance, good health for you in these times, 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. The computation method is also touched on. Hence, we need to move along and start to include the antenna with our testing. 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. The overall lenght is only 15m. . It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. One possible explanation is that the core losses drop with temperature. 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. 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. 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. And not all hf antenna installation are same, with most requiring bit of tinkering. 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. Thanks again Jim. View the job description, responsibilities and qualifications for this position. 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. Next, I started winding the transformer. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. There is much more that can be written about this antenna and its matching, but that was not my aim. Do I count the six loops around the pvc in the measurement? 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 dont have an amplifier, so only need to be able to handle 100W. 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. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. Why had I not noticed this before? IIRC they call it a "compensator". With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. 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. coil inductance calculator at 66pacific.com. Research salary, company info, career paths, and top skills for Software Engineer - EDI Start by wrapping the wire around the toroid. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The cooling curve I measured is shown below. The toroid with its many taps may be soldered directly on a multi-position switch. = 258 * 10^-12. 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. The SWR for the 20 meter EFHW antenna was < 1.2:1 Check your inbox or spam folder to confirm your subscription. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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. (LogOut/ I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. I decided to push for best efficiency with a 5-turn primary. 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. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 1. It uses a coil as a compensation unit, and no counterpoise. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. We do not know what the actual impedance will be at the end of the antenna radiator. 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. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. I tossed the line as far up as I could in a tree. All Rights Reserved. The combination of the transformer with the end-fed dipole results in a positive reactance. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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. 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. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. 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. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. This provides proper insulation from the relatively high voltages on the seconder winding. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. 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. What are the advantages and disadvantages of the end-fed half wave antenna? 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. stream 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 came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. 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.
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