Hence, there is no optimum single-fit solution. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . The highest frequency could be14.350MHz. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. . I mounted the transformer on a tree for testing. Lets call this element the LoadAttenuator. With such a switch, it is impossible to forget to switch back to operational mode. P.S. ROB@COMCOIL.COM In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. We use cookies to optimize our website and our service. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. EFHW 80m extension - MI0KXX I wish I had a simple answer, but really this is where some experimentation can pay off. There is much more that can be written about this antenna and its matching, but that was not my aim. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. You cant really see the antenna wire, but the red line shows the antenna path. Small efficient matching transformer for an EFHW - owenduffy.net The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 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. 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). Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. 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. Basu Bhattacharya (VU2NSB). 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. 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. Taking the time derivative of the above equation you get the power dissipation. It is not necessary to calculate the above; the results are sown in the following table. I used the 14g enameled wire and wound it on the FT240-43. I look at the end-fed as just an extreme example of an off-center-fed antenna. It requires a set distance to hang both ends of the antenna, and that is not always given. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. Contact Commercial Coils These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. I am currently working on measurements of an EFHW antenna. The antenna is effective and the materials and construction are of a very high quality. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Best regards and thanks again for your comment. 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. 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. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. 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. 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 resistance (real) component of the impedance is right where we want it near 50 ohms. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. But systems that work better increase the prospects of contacts. <> Why had I not noticed this before? The 2 coils are 35uh and 90uh. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. 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. 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. Can a diode be used to rectify signals smaller than its threshold voltage? PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex . Do I count the six loops around the pvc in the measurement? Could it be something to do with the new vertical aerial I had recently installed? 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. Even at 15W the voltage at the ends may reach 100-200V. Copyright 2014-2023. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. Change), You are commenting using your Twitter account. The Truth, ,and Nothing But The Truth (as I've experienced it) A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? 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. A Smith chart view of EFHW transformer compensation Below is the schematic of the final build. 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. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. 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). It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. How big and where to place it is likely best determined empirically. We do not know what the actual impedance will be at the end of the antenna radiator. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. One way or another there is always a counterpoise involved if the antenna is tuned correctly. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. My question is what is 'higher frequency' specifically? Finally the tank circuits specification is complete, which is sown below. First, note that the transformer has low transmission loss up to nearly 50MHz. The technical storage or access that is used exclusively for anonymous statistical purposes. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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. Thank you for an interesting and informative read. I installed a QRP SWR meter into the tuner that makes tuning very handy. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite For the last step, I put together a RF choke to use between the radio and the feedline. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. 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. 100W on a Wire Antenna - How far would it reach? The 40-10m EFHW camping antenna is late but done. More info in - reddit 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 purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. Most of the time 5 to 20W will be adequate for activation anyway. Instead, this shifts everything down and makes it very easy to tune 10m. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 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. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. Above 7MHz, there is very little temperature dependence at all. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. This antenna is working for 80,40,20,10 and 6m bands. Research salary, company info, career paths, and top skills for Software Engineer - EDI Many people use an inductor placed at the near end to make things level out on the higher bands. 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. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. It uses a coil as a compensation unit, and no counterpoise. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. They will be adjusted for resonance at or close to the CW portion of the bands. The highest voltages as well as radiation are also at the end of the antenna wire. How to tune a multi-band EFHW antenna using a loading coil Some website features may not function optimally without cookies. Basically, the loading coil is operating as a trap. By using traps, the antenna works on all three bands with no operator interaction. 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. 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. To be safe, better not get much above 120 C. Regards VE9HAM. Z8Vq9_@x C\Agv#. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Trapped five band EFHW SOTA antenna | VK3IL Blog If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. 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. I then added two 220pf capacitors in series between the center conductor and ground. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. The bridge than will measure zero voltage across the bridge, and the LED will turn off. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 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. Above is a sweep of the roughly compensated transformer. I will go back and have the article corrected. EFHW Compensation Coil Experiment - YouTube I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD 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. 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 article will not address that antenna type. 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 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 Although it is simple to build and is a multiband antenna, it has several attributes that . 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. Low SSN Why do most Hams find HF Radio so difficult? This will yield the maximum capacity of the variable capacitor. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. There are two aspects, however that we need to consider: Lets begin with the transformer. The equation in the article is corrected now. 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. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. 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. High Q, hence low loss. Is FT8 popularity growing at the cost of SSB Phone and CW? Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. I added some Christmas colored zip ties to hold everything in place. 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.
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