The SWR figures were as follows: FT240-43 132ft/100pF capacitor Apply for the Job in Software Engineer - EDI at St. Louis, MO. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube You cant really see the antenna wire, but the red line shows the antenna path. I look at the end-fed as just an extreme example of an off-center-fed antenna. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. 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. 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'. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. Impressive article and so well done that I may give it a try. The coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 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. Im very happy with the result. How big and where to place it is likely best determined empirically. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. The Truth, ,and Nothing But The Truth (as I've experienced it) The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The radiation pattern of this antenna on most bands produces multiple lobes. The antenna is effective and the materials and construction are of a very high quality. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Let us touch on some necessary theory to begin with. Consequently, this is how the capacitance values are determined. And of course, a counterpoise with various lengths. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. We do not know what the actual impedance will be at the end of the antenna radiator. Thanks in advance, good health for you in these times, 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??). The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). How to get started on ISS Cross band Repeater? % This antenna is working for 80,40,20,10 and 6m bands. 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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). 2006. 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. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. ON7EQ EFHW Antenna - qsl.net So the differences I see in the data sheets hysteresis curves are not the correct explanation. I installed a QRP SWR meter into the tuner that makes tuning very handy. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. 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. This is typically a weak spot. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Lets call this element the LoadAttenuator. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. EFHW Compensation Coil Experiment - YouTube 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. The overlaid VSWR plots are shown below. Hence, we need to move along and start to include the antenna with our testing. As is often the case, packaging was determined by what boxes I had laying around. 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. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. P.S. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. 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. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. 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. clear. And not all hf antenna installation are same, with most requiring bit of tinkering. Even at 15W the voltage at the ends may reach 100-200V. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Efhw Compensation Coil Experiment - Local Search Denver Post 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. 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 End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I added some Christmas colored zip ties to hold everything in place. I am planning to use this latest one at the Field Day next year. 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. That is an end-fed, but very different then the half wave construction. Thanks for your comments. 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. See the table above. Thanks again Jim. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. 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. The EFHW transformer box from outside. It performed well on both the 2m and 70cm bands. One end is about 5 meters high on an extended fishing pole. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. The SWR results are as follows: Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. The transformer fits sideways in the box with a few millimeters to spare. i liked it a lot, you give good ideas, many thanks. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. The Counterpoise is a short, typically one twentieth (0.05 *. ) It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. (LogOut/ So, I embarked on testing it for myself. = 258 * 10^-12. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. This article will not address that antenna type. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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. Show more. Does your station desperately need a good RF ground to behave properly? The latest news about Efhw Compensation Coil Experiment. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. I first mounted the SO239 connector to the box. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Now I just need to build or acquire a decent radio to utilize this new antenna. The technical storage or access that is used exclusively for anonymous statistical purposes. It is important to consider the voltages on this tank circuit. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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 was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The worse SWR was 1:1.7 at the top end of 20 meters. It is recommended to use at least 2W non-inductive resistors for this purpose. Taking the time derivative of the above equation you get the power dissipation. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? They will be adjusted for resonance at or close to the CW portion of the bands. It should be no surprise that 80pF is close to optimal. It is not necessary to calculate the above; the results are sown in the following table. Looking at several builds and discussions, such as commercial antennas (e.g. Change). If you stare at the above frequency sweeps you will discover a few things. This will yield the minimal capacitance of the variable capacitor. Z8Vq9_@x C\Agv#. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. However, a key restriction is its 25W power rating, due to the small matching transformer. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 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. The technical storage or access that is used exclusively for statistical purposes. Just the bare 80m wire is shown in red. 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. 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. Software Engineer - EDI - salary.com Transmitting on 15 meters was impossible because of RF into the radio. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It is important that resonance may be achieved at each tap of the inductance. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. By using traps, the antenna works on all three bands with no operator interaction. Wrap the first wire around the toroid 27 times (I used a black wire for this). I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. 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. 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. Below is the schematic of the final build. Hi Ajai, The SWR was measured for each of the three antennas across the CW portion of the bands. Look at the compensation coil slide. I settled on a compact secondary using #28 wire. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 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. 100W on a Wire Antenna How far would it reach? The next important parameter is the parallel resonant circuits resonant frequency. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Elnzst krnk, de elsikkadt az zenete. Low SSN Why do most Hams find HF Radio so difficult? However, I think I made a good choice with a Hammond 1590A diecast aluminum box. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. After some internet research, I settled on making the former from a paint roller. Can I get away with no capacitor in my design? How-To: Make a Multiband EFHWA for Amateur Ham Radio It uses a coil as a compensation unit, and no counterpoise. I am currently working on measurements of an EFHW antenna. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. More designs can be found by Googling "80m loaded dipole.". Above is a thermograph of the transformer at 20W input at 3.6MHz. Do I count the six loops around the pvc in the measurement? Most informative and appreciated. 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. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Research salary, company info, career paths, and top skills for Software Engineer - EDI The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Engineering the EFHW 49:1 Transformer and Antenna I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). My End-Fed Half-Wave (EFHW) AmateurRadio.com Some hams swear by them, yet some completely demean it. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. This is perhaps one of the most hotly debated rookie topics in. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. I dont have an amplifier, so only need to be able to handle 100W. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Why had I not noticed this before? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. This gave me an effective coil diameter of 40.5mm. Change), You are commenting using your Twitter account. Thirty turns #28 are wound on the two FT114-43 cores. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Csatlakozz csapatunkhoz! I tossed the line as far up as I could in a tree. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. (LogOut/ 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. Thank you for your comment and feedback on the article about the EFHW antenna. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands.
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