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The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I mounted the transformer on a tree for testing. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. However, the insertion loss of the packaged transformer would be intolerable on the 10 meter band if it appeared the same way with an antenna wire connected. It performed well on both the 2m and 70cm bands. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. So I built myself an improved replacement matching transformer. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Looking at several builds and discussions, such as commercial antennas (e.g. 100W on a Wire Antenna How far would it reach? I decided to play with this to see what I could accomplish. 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. (LogOut/ The original coil is designed for low power portable applications. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Graphed with a log scale, it makes a nice straight line. Zin=46.52+j6.72. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Show more. Change), You are commenting using your Facebook account. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Check your inbox or spam folder to confirm your subscription. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. With such a switch, it is impossible to forget to switch back to operational mode. 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. A short 80m antenna for my lot - KB6NU's Ham Radio Blog The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . The biggest uncertainty in these measurements was the actual power level used. %PDF-1.4 From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. Some website features may not function optimally without cookies. 100W on a Wire Antenna - Is it good enough for DX? Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Im very pleased with that indeed. 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. 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. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. For a quarter wave that is about 8 nS. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. The resistance (real) component of the impedance is right where we want it near 50 ohms. Why had I not noticed this before? 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??). 73! 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. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. 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. 2 0 obj Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. Highest frequency = 14.350 MHz. The End-Fed Half Wave Antenna a bit Differently A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Independent Medical Evaluation - IME | Cynthia Hennessey Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. 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. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. Nagyon j ez a cikk. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. 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. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. The real power limit will be core heating. The results are presented below. 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 is important to consider the voltages on this tank circuit. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. Start by wrapping the wire around the toroid. 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. Is FT8 popularity growing at the cost of SSB Phone and CW? It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Just the bare 80m wire is shown in red. <> 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. That will be the missing resistor in the resistor bridge of the below circuit. I decided to play with this to see what I could accomplish. 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A 100pF silvered mica was connected in shunt with the transformer . It is not necessary to calculate the above; the results are sown in the following table. Does your station desperately need a good RF ground to behave properly? I also will ask, why didnt it work for you. stream Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. 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'. Be cautious, such voltages may cause a quite painful skin scorch. 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. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. 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. 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. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. 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. See the second completed tuner depicted below. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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 final turns ratio turned out to be 3:29. (LogOut/ Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Finally the tank circuits specification is complete, which is sown below. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. The overall lenght is only 15m. Above 7MHz, there is very little temperature dependence at all. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. : I see you were able to post your comment now, so I just copied my email answer here for others to see. I am planning to use this latest one at the Field Day next year. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. I can give a link if you need. With no counterpoise wire it will be the coaxs shield providing it. Very interesting design. Make sure the first wire is wrapped evenly around the whole toroid. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Taking the time derivative of the above equation you get the power dissipation. 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. I wish you lots of productive experimentations and successful portable operations. 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). Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer You cant really see the antenna wire, but the red line shows the antenna path. 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. Krem, rja le, mi a krdse. One possible explanation is that the core losses drop with temperature. I would mention first its ease of installation. One end is about 5 meters high on an extended fishing pole. The EFHW transformer box from outside. 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. 5) It is very hard to avoid stray capacitance on the output. Even at 15W the voltage at the ends may reach 100-200V. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Why had I not noticed this before? In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Trapped five band EFHW SOTA antenna | VK3IL Blog There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. 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. 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. 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. Can a diode be used to rectify signals smaller than its threshold voltage? The impedance matching circuit is essentially a simple parallel resonant LC circuit. 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. Thank you for your comment and feedback on the article about the EFHW antenna. However, it has its idiosyncrasies. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former.