efhw compensation coil efhw compensation coil

Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Thank you for your comment and feedback on the article about the EFHW antenna. How to get started on ISS Cross band Repeater? This is typically a weak spot. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. The basic question before us is how does an antenna work? 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. Thanks for your comments. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. 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. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. Lets call this element the LoadAttenuator. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . ROB@COMCOIL.COM Instead, this shifts everything down and makes it very easy to tune 10m. Check your inbox or spam folder to confirm your subscription. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. 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. 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. 100W on a Wire Antenna - Is it good enough for DX? Below is the schematic of the final build. These dimensions were derived from modelling the antenna in EZNEC. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Is it any good? The transformer fits sideways in the box with a few millimeters to spare. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. We also need to know what are the frequencies or bands for which we plant to use this antenna. Why does antenna radiation occur? It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Which begs the question what happens when you attach the antenna? Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The SWR results are as follows: 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. It uses a coil as a compensation unit, and no counterpoise. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. 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'. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Im very pleased with that indeed. 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. Isn't it? Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. 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. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. This reveals we only need to compensate for the reactive component. 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. 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. 100W on a Wire Antenna - How far would it reach? Can a diode be used to rectify signals smaller than its threshold voltage? 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. Regards VE9HAM. This antenna is only 15m long using 2 loading coils. Workers' Comp. 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. 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). A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Yes, indeed EFHW antennas are very useful for SOTA or other field operation. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. It does not need any special components; in fact, most of us may have them in our shack drawers already. First, note that the transformer has low transmission loss up to nearly 50MHz. However, a key restriction is its 25W power rating, due to the small matching transformer. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). It performed well on both the 2m and 70cm bands. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 73 At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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. How badly can high Local Ambient QRM affect HF Radio? One end is about 5 meters high on an extended fishing pole. Start by wrapping the wire around the toroid. The equation in the article is corrected now. I was curious why this capacitor was added to the transformer. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. I installed a QRP SWR meter into the tuner that makes tuning very handy. 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. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. 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. The photos above show a method that works fairly well. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Best regards and thanks again for your comment. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. A 100pF silvered mica was connected in shunt with the transformer primary. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. I am planning to use this latest one at the Field Day next year. 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. The wire as I strung it up seemed to resist having a good SWR for the 20m band. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). View the job description, responsibilities and qualifications for this position. The antenna is up. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Highest frequency = 14.350 MHz. Also find news related to Efhw Compensation Coil Experiment which is trending today. Look at the compensation coil slide. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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. 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. High Q, hence low loss. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Let us touch on some necessary theory to begin with. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. 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. I tossed the line as far up as I could in a tree. 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. 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. Change), You are commenting using your Facebook account. I also will ask, why didnt it work for you. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Cmzett: Weince joseph How can we help? You can start with the links below. Most informative and appreciated. The overlaid VSWR plots are shown below. 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. 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 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Proudly created withWix.com. We do not know what the actual impedance will be at the end of the antenna radiator. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Hence, we need to move along and start to include the antenna with our testing. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Very interesting design. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. I wish you lots of productive experimentations and successful portable operations. On the transformer, I added a few wingnuts to tighten down the antenna wire. Thanks! I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! 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. See the table above. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. In theory, the examination is supposed to be used to help clarify your medical condition and . 2006. %PDF-1.4 High self-resonant frequency. 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 A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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 SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Hello, a wonderful approach for the problems.. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Could it be something to do with the new vertical aerial I had recently installed? I used four parallel #28 wires (not twisted) for the primary. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 3) Total losses are approximately independent of core volume. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. There is much more that can be written about this antenna and its matching, but that was not my aim. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! This gave me an effective coil diameter of 40.5mm. The highest voltages as well as radiation are also at the end of the antenna wire. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. What are its disadvantages? Refurbishing aluminium antenna parts affected by weather / corrosion. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Krem, rja le, mi a krdse. 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. Even at 15W the voltage at the ends may reach 100-200V. 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%. nanoVNA-H can firmware be updated if it has a broken USB socket?