The transformer fits sideways in the box with a few millimeters to spare. 2015. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. You can see the coil in the picture below (red arrow). To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Taking the time derivative of the above equation you get the power dissipation. 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. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. It uses a coil as a compensation unit, and no counterpoise. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. By using traps, the antenna works on all three bands with no operator interaction. Most of the time 5 to 20W will be adequate for activation anyway. I checked the wall brackets and mast, but all the fixings were nice and tight. Zin=46.52+j6.72. It is not necessary to calculate the above; the results are sown in the following table. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Above, 3t on the primary delivers Gcore<0.002S. . This antenna is only 15m long using 2 loading coils. <> 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. The SWR results are as follows: Change), You are commenting using your Twitter account. It requires a set distance to hang both ends of the antenna, and that is not always given. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Start by wrapping the wire around the toroid. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Hi Ajai, If you stare at the above frequency sweeps you will discover a few things. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The toroid with its many taps may be soldered directly on a multi-position switch. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. However, a key restriction is its 25W power rating, due to the small matching transformer. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Thanks for your comments. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. This will also be handling 100W. From that we can find Mismatch Loss. How badly can high Local Ambient QRM affect HF Radio? Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? 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. A week or two later I started to notice an occasional knocking sound inside the house. . And not all hf antenna installation are same, with most requiring bit of tinkering. One possible explanation is that the core losses drop with temperature. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Basically, the loading coil is operating as a trap. 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 . It not a loading coil. Hence, there is no optimum single-fit solution. I will go back and have the article corrected. Klubunknl folyamatos a tagfelvtel. What kind of balun is this? The equation in the article is corrected now. 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. Thank you for your comment and feedback on the article about the EFHW antenna. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Understanding Antennas The Good, the Bad, and the Ugly. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I wish I had a simple answer, but really this is where some experimentation can pay off. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. However, it has its idiosyncrasies. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. 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 computation method is also touched on. This antenna is working for 80,40,20,10 and 6m bands. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. View the job description, responsibilities and qualifications for this position. 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 mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. The photos above show a method that works fairly well. Wrap the first wire around the toroid 27 times (I used a black wire for this). Below is the schematic of the final build. The antenna is effective and the materials and construction are of a very high quality. I first mounted the SO239 connector to the box. Be sure to take a look for additional analysis and conclusions. So, how to construct an end-fed half wave antenna? Some hams swear by them, yet some completely demean it. Do I count the six loops around the pvc in the measurement? Looking at several builds and discussions, such as commercial antennas (e.g. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. Thirty turns #28 are wound on the two FT114-43 cores. It may be one or even five kilo-ohms. More designs can be found by Googling "80m loaded dipole.". The SWR was measured for each of the three antennas across the CW portion of the bands. The Counterpoise is a short, typically one twentieth (0.05 *. ) The SWR figures were as follows: FT240-43 132ft/100pF capacitor 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. 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. PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. 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. 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. of the wavelength. Could it be something to do with the new vertical aerial I had recently installed? 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. Lowest measured inductivity = 2.0 H. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. = .00 00 00 00 0 258 It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. Z8Vq9_@x C\Agv#. The bridge than will measure zero voltage across the bridge, and the LED will turn off. Be cautious, such voltages may cause a quite painful skin scorch. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Can a diode be used to rectify signals smaller than its threshold voltage? 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 2 0 obj 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. This reveals we only need to compensate for the reactive component. 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. Let us touch on some necessary theory to begin with. 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. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. The results are shown below. I assume you know the GNARC source for EFHW antennas. 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. Workers' Comp. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! It depends on the selection of the inductance and the capacitor values. 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. 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). I used the 14g enameled wire and wound it on the FT240-43. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. This suggests an inductive reactance. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Thank you for an interesting and informative read. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. My design objectives were: 1. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. Looking at several builds and discussions, such as commercial antennas (e.g. I will publish my findings, but I cannot not promise to complete it until early fall. There are many good descriptions on the net about this type of antenna. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Is FT8 popularity growing at the cost of SSB Phone and CW? : I see you were able to post your comment now, so I just copied my email answer here for others to see. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. My favorite SOTA antenna is the End-Fed Half Wave Antenna. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. All Rights Reserved. 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. 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. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 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. 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. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. The antenna is effective and the materials and construction are of a very high quality. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. Hello, a wonderful approach for the problems.. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The technical storage or access that is used exclusively for anonymous statistical purposes. 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. 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. 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 cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure.
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