For the last step, I put together a RF choke to use between the radio and the feedline. Just the bare 80m wire is shown in red. Thanks in advance, good health for you in these times, This is perhaps one of the most hotly debated rookie topics in. The antennas are set up as a sloper as in my SOTA outings. 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. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. The wire as I strung it up seemed to resist having a good SWR for the 20m band. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. 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. 2 0 obj 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. 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 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. 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. The cooling curve I measured is shown below. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 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 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. I checked the wall brackets and mast, but all the fixings were nice and tight. The antenna is effective and the materials and construction are of a very high quality. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. 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. As is often the case, packaging was determined by what boxes I had laying around. Why had I not noticed this before? 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. Jim, do you mind if I add your email and my answer as a comment to the article? The highest voltages as well as radiation are also at the end of the antenna wire. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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. Does your station desperately need a good RF ground to behave properly? 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. Above, 3t on the primary delivers Gcore<0.002S. 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 informative and appreciated. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I found it very useful to label the tuner with switch and capacitance positions. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Can a diode be used to rectify signals smaller than its threshold voltage? Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. = 258 * 10^-12. 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. Start by wrapping the wire around the toroid. It is worth experimenting with its length also. The EFHW transformer box from outside. 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. 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. It is not necessary to calculate the above; the results are sown in the following table. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Very interesting design. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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. Proudly created withWix.com. 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. Hence, we need to move along and start to include the antenna with our testing. 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. The bridge than will measure zero voltage across the bridge, and the LED will turn off. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. But systems that work better increase the prospects of contacts. And not all hf antenna installation are same, with most requiring bit of tinkering. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. Some hams swear by them, yet some completely demean it. 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. Hence, there is no optimum single-fit solution. So I built myself an improved replacement matching transformer. And of course, a counterpoise with various lengths. By using traps, the antenna works on all three bands with no operator interaction. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Could it be something to do with the new vertical aerial I had recently installed? Apply for the Job in Software Engineer - EDI at St. Louis, MO. 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. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. I will go back and have the article corrected. The final turns ratio turned out to be 3:29. To further improve the flux linkage, I wound the primary on top of the secondary. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Can I get away with no capacitor in my design? 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. %PDF-1.4 On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). As I reexamined my formula, you pointed it out correctly, there is an error in it. 100W on a Wire antenna! 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. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. No capacitor was installed. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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 decided to push for best efficiency with a 5-turn primary. The overall lenght is only 15m. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 3) Total losses are approximately independent of core volume. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. 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. If not a lightning strike, I will write an article about the experience as well. To be safe, better not get much above 120 C. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Regards VE9HAM. Krem, rja le, mi a krdse. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. The difference here is that the target bands are low frequency. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. It performed well on both the 2m and 70cm bands. 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). Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. It requires a set distance to hang both ends of the antenna, and that is not always given. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Change), You are commenting using your Twitter account. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. In theory, the examination is supposed to be used to help clarify your medical condition and . I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I also will ask, why didnt it work for you. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. High self-resonant frequency. 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. Let me review the salient observations from the previous work. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. How does this SWR meter works? This will yield the maximum capacity of the variable capacitor. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF.
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