efhw compensation coil efhw compensation coil

Let us touch on some necessary theory to begin with. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. Nagyon j ez a cikk. This can then, fed with coaxial cable, in many cases be . 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Consequently, this is how the capacitance values are determined. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. . Thank you for an interesting and informative read. VSWR<1.8 over all of HF. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. The overlaid VSWR plots are shown below. 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. This will yield the minimal capacitance of the variable capacitor. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. The band compensating inductor placed on the wire is another story. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Be cautious, such voltages may cause a quite painful skin scorch. 1. The SWR was measured for each of the three antennas across the CW portion of the bands. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. ROB@COMCOIL.COM 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 also will ask, why didnt it work for you. Subscribe to our newsletter and receive regular updates on new posts and articles. This gave me an effective coil diameter of 40.5mm. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. 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. I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. 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. Let's find out! The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. Lets call this element the LoadAttenuator. I look at the end-fed as just an extreme example of an off-center-fed antenna. 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. 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. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. 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. I first mounted the SO239 connector to the box. It performed well on both the 2m and 70cm bands. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. The final turns ratio turned out to be 3:29. 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. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! What kind of balun is this? Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. No capacitor was installed. Understanding Antennas The Good, the Bad, and the Ugly. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. This is perhaps one of the most hotly debated rookie topics in. %PDF-1.4 Frank VK1VK. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Graphed with a log scale, it makes a nice straight line. 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. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Elnzst krnk, de elsikkadt az zenete. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. And not all hf antenna installation are same, with most requiring bit of tinkering. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Basu Bhattacharya (VU2NSB). 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. 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. I decided to play with this to see what I could accomplish. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. Z8Vq9_@x C\Agv#. By using traps, the antenna works on all three bands with no operator interaction. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The technical storage or access that is used exclusively for statistical purposes. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 100W on a Wire Antenna How far would it reach? 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The cooling curve I measured is shown below. Workers' Comp. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. I added some Christmas colored zip ties to hold everything in place. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. I used the 14g enameled wire and wound it on the FT240-43. 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 . In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. This will yield the maximum capacity of the variable capacitor. My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? However, a key restriction is its 25W power rating, due to the small matching transformer. I checked the wall brackets and mast, but all the fixings were nice and tight. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. One end is about 5 meters high on an extended fishing pole. 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. = 1/30.e6 = 33 nS. 100W on a Wire Antenna - How far would it reach? If you really want to get the heat out, add some fins to the aluminum box. 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Thanks for your comments. Above, 3t on the primary delivers Gcore<0.002S. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. (LogOut/ Lets do a quick calculation to see how much an issue is this output capacitance. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. How far could it possibly reach? I was curious why this capacitor was added to the transformer. I checked the wall brackets and mast, but all the fixings were nice and tight. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Is FT8 popularity growing at the cost of SSB Phone and CW? In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. 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. 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? At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. 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. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. = 258 * 10^-12. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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 finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching 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. Show more. 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. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none.