This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. The latest news about Efhw Compensation Coil Experiment. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. . Let us touch on some necessary theory to begin with. What are the advantages and disadvantages of the end-fed half wave antenna? 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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. 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. 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. Which begs the question what happens when you attach the 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. This is typically a weak spot. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Thank you for an interesting and informative read. I used the 14g enameled wire and wound it on the FT240-43. In theory, the examination is supposed to be used to help clarify your medical condition and . This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. This will also be handling 100W. . The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. And now I am planning to build one for 160/80m. This will yield the minimal capacitance of the variable capacitor. A 100pF silvered mica was connected in shunt with the transformer . I used four parallel #28 wires (not twisted) for the primary. I will publish my findings, but I cannot not promise to complete it until early fall. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. We need to measure the inductances of the toroid with the tapped coil. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. 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. These dimensions were derived from modelling the antenna in EZNEC. Could it be something to do with the new vertical aerial I had recently installed? Csatlakozz csapatunkhoz! Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. So, I embarked on testing it for myself. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. 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. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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. It should be no surprise that 80pF is close to optimal. The radiation pattern of this antenna on most bands produces multiple lobes. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. It requires a set distance to hang both ends of the antenna, and that is not always given. 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. The band compensating inductor placed on the wire is another story. 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. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Why had I not noticed this before? The worse SWR was 1:1.7 at the top end of 20 meters. We use cookies to optimize our website and our service. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF 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). First, note that the transformer has low transmission loss up to nearly 50MHz. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. It is not necessary to calculate the above; the results are sown in the following table. There are two aspects, however that we need to consider: Lets begin with the transformer. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. So the differences I see in the data sheets hysteresis curves are not the correct explanation. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Change), You are commenting using your Twitter account. The antenna is effective and the materials and construction are of a very high quality. [email protected] The SWR for the 20 meter EFHW antenna was < 1.2:1 The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. stream 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. 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. 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. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. I particularly want to know how counterpoise affects the common mode currents on the coax. Start by wrapping the wire around the toroid. Then I covered the coil in kapton tape to hold it together. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. It is recommended to use at least 2W non-inductive resistors for this purpose. Consequently, this is how the capacitance values are determined. It is all about getting the heat out. 2015. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. (LogOut/ Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. Some website features may not function optimally without cookies. 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??). 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. We also need to know what are the frequencies or bands for which we plant to use this antenna. A radio station is as good or as bad as the antenna it has. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. The final turns ratio turned out to be 3:29. As is often the case, packaging was determined by what boxes I had laying around. 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 . You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. The 2 coils are 35uh and 90uh. 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. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. The final turns ratio turned out to be 3:29. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Thanks again Jim. I will go back and have the article corrected. A week or two later I started to notice an occasional knocking sound inside the house. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. It may be one or even five kilo-ohms. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. 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. Some say you do not need a counterpoise, but that is false. 100W on a Wire Antenna - Is it good enough for DX? But I would caution its usage for higher power than 10-15W. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I decided to push for best efficiency with a 5-turn primary. 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? 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. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). A method for estimating the impedance of a ferrite cored toroidal inductor at RF. View the job description, responsibilities and qualifications for this position. How badly can high Local Ambient QRM affect HF Radio? 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. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. See the second completed tuner depicted below. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. How far could it possibly reach? 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. Is it any good? How does this SWR meter works? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Elnzst krnk, de elsikkadt az zenete. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. 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. Trapped five band EFHW SOTA antenna. 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. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Two layers of 1mil Kapton tape are placed over the winding. However, it has its idiosyncrasies. Be sure to take a look for additional analysis and conclusions. There is much more that can be written about this antenna and its matching, but that was not my aim. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. Below is the schematic of the final build. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The equation in the article is corrected now. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. 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. I am building an EFHW antenna for my new. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. I added some Christmas colored zip ties to hold everything in place. Will there be the same performance for single band EFHWs? It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Hence, we need to move along and start to include the antenna with our testing. Some hams swear by them, yet some completely demean it. 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. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 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. 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. 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. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Let me review the salient observations from the previous work. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Your posting put it all together for meTHANK YOU!!!! In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. From that we can find Mismatch Loss. The original coil is designed for low power portable applications. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Why had I not noticed this before? Select components with good insolating materials and properly chosen, relatively high voltage rated parts. Compensation. With no counterpoise wire it will be the coaxs shield providing it. Also find news related to Efhw Compensation Coil Experiment which is trending today. Looking at several builds and discussions, such as commercial antennas (e.g. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. You cant really see the antenna wire, but the red line shows the antenna path. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. 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. 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. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. By using traps, the antenna works on all three bands with no operator interaction. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. However, a key restriction is its 25W power rating, due to the small matching transformer. 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'. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Taking the time derivative of the above equation you get the power dissipation. Check your inbox or spam folder to confirm your subscription. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. 2. I checked the wall brackets and mast, but all the fixings were nice and tight. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Research salary, company info, career paths, and top skills for Software Engineer - EDI The antenna is effective and the materials and construction are of a very high quality. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. In his article, I will try to bust some of the myths associated with Inverted. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. Not the ideal antenna, but convenient!

Jackie Hill Perry Husband, Paul Skjodt Net Worth, Peanut Butter Whiskey And Dr Pepper, Scorpio Rising Woman Dressing Style, How Many Times Has John Michael Higgins Been Married, Articles E