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 End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. With such a switch, it is impossible to forget to switch back to operational mode. 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. I am planning to use this latest one at the Field Day next year. Although it is simple to build and is a multiband antenna, it has several attributes that . I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. It performed well on both the 2m and 70cm bands. How badly can high Local Ambient QRM affect HF Radio? 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. Above is a thermograph of the transformer at 20W input at 3.6MHz. 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. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. I checked the wall brackets and mast, but all the fixings were nice and tight. The cooling curve I measured is shown below. Thank you for an interesting and informative read. 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. Some say you do not need a counterpoise, but that is false. This will yield the minimal capacitance of the variable capacitor. I then added two 220pf capacitors in series between the center conductor and ground. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. The SWR was measured for each of the three antennas across the CW portion of the bands. I assume you know the GNARC source for EFHW antennas. The results are shown below. The highest voltages as well as radiation are also at the end of the antenna wire. 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. It performed well on both the 2m and 70cm bands. 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). But systems that work better increase the prospects of contacts. 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Best regards and thanks again for your comment. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. 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. Do I count the six loops around the pvc in the measurement? The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 73! In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. We need to measure the inductances of the toroid with the tapped coil. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Your posting put it all together for meTHANK YOU!!!! The highest frequency could be14.350MHz. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. You cant really see the antenna wire, but the red line shows the antenna path. Let us touch on some necessary theory to begin with. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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. 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. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. How does this SWR meter works? It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. It is important to consider the voltages on this tank circuit. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. The previous table already contains these measurements. |k"^N>F.AnJkJsq'PV}o0I. 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 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. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. If you really want to get the heat out, add some fins to the aluminum box. All Rights Reserved. Im very pleased with that indeed. The resistance (real) component of the impedance is right where we want it near 50 ohms. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Why had I not noticed this before? It not a loading coil. The model results show the need for a not entirely insignificant counterpoise. The SWR results are as follows: 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. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. 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. Instead, this shifts everything down and makes it very easy to tune 10m. 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. nanoVNA-H can firmware be updated if it has a broken USB socket? Thirty turns #28 are wound on the two FT114-43 cores. 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. coil inductance calculator at 66pacific.com. 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. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. So, how to construct an end-fed half wave antenna? The antennas are set up as a sloper as in my SOTA outings. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. It does not need any special components; in fact, most of us may have them in our shack drawers already. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. blue: 250pF, to much compensation. The band compensating inductor placed on the wire is another story. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. My question is what is 'higher frequency' specifically? A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. 2006. A ktelez mezket * karakterrel jelltk. 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. How far could it possibly reach? This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. 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. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. I will go back and have the article corrected. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Basically, the loading coil is operating as a trap. Make sure the first wire is wrapped evenly around the whole toroid. Taking the time derivative of the above equation you get the power dissipation. Many people use an inductor placed at the near end to make things level out on the higher bands. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. <> 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. I found it very useful to label the tuner with switch and capacitance positions. Nagyon j ez a cikk. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. 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 did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH The equation should have a 10^6 and not 10^-6 in the nominator. Isn't it? 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. 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. And of course, a counterpoise with various lengths. This will also be handling 100W. = .00 00 00 00 0 258 Impressive article and so well done that I may give it a try. (LogOut/ 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. You can start with the links below. Above 7MHz, there is very little temperature dependence at all. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Hence, there is no optimum single-fit solution. The equation in the article is corrected now. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. P.S. application of Kirchhoff's current Law on a typical EFHW antenna configuration. More designs can be found by Googling "80m loaded dipole.". In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. 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. Understanding Antennas The Good, the Bad, and the Ugly. With no counterpoise wire it will be the coaxs shield providing it. After some internet research, I settled on making the former from a paint roller. 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 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 was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. The wire as I strung it up seemed to resist having a good SWR for the 20m band. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. This will yield the maximum capacity of the variable capacitor. This antenna is working for 80,40,20,10 and 6m bands. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I decided to play with this to see what I could accomplish. To be safe, better not get much above 120 C. 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. 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. That is an end-fed, but very different then the half wave construction. 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 coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. Csatlakozz csapatunkhoz! 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. Two layers of 1mil Kapton tape are placed over the winding. Low SSN Why do most Hams find HF Radio so difficult? The final turns ratio turned out to be 3:29. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! Does your station desperately need a good RF ground to behave properly? The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Basu Bhattacharya (VU2NSB). The antenna is up. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. Let me review the salient observations from the previous work. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. To further improve the flux linkage, I wound the primary on top of the secondary. 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? 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. 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. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 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. Krem, rja le, mi a krdse. The final turns ratio turned out to be 3:29. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. The computation method is also touched on. Of course, you will need to find your tuning positions and apply your own position scale. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. And not all hf antenna installation are same, with most requiring bit of tinkering. It is not necessary to calculate the above; the results are sown in the following table. The antenna is effective and the materials and construction are of a very high quality. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. VSWR<1.8 over all of HF. The latest news about Efhw Compensation Coil Experiment. Looking at several builds and discussions, such as commercial antennas (e.g. The technical storage or access that is used exclusively for anonymous statistical purposes. 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. 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). I will publish my findings, but I cannot not promise to complete it until early fall. Lowest frequency = 7.000 MHz. This can then, fed with coaxial cable, in many cases be .

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