You cant really see the antenna wire, but the red line shows the antenna path. . Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. 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 results are presented below. It is not necessary to calculate the above; the results are sown in the following table. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-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. One end is about 5 meters high on an extended fishing pole. Basu Bhattacharya (VU2NSB). Let us touch on some necessary theory to begin with. The band compensating inductor placed on the wire is another story. Is FT8 popularity growing at the cost of SSB Phone and CW? I fashioned an antenna connector with washers made from some acrylic rod I had on hand. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. The next important parameter is the parallel resonant circuits resonant frequency. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. The SWR was measured for each of the three antennas across the CW portion of the bands. Change), You are commenting using your Facebook account. 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. = 1/30.e6 = 33 nS. 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. There is lot of controversy around the EFHW antennas. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. I mounted the transformer on a tree for testing. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. Could it be something to do with the new vertical aerial I had recently installed? is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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. Frank VK1VK. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? They will be adjusted for resonance at or close to the CW portion of the bands. I added some Christmas colored zip ties to hold everything in place. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. I am planning to use this latest one at the Field Day next year. 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. These dimensions were derived from modelling the antenna in EZNEC. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Highest frequency = 14.350 MHz. I assume you know the GNARC source for EFHW antennas. 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. application of Kirchhoff's current Law on a typical EFHW antenna configuration. How big and where to place it is likely best determined empirically. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. The final turns ratio turned out to be 3:29. It performed well on both the 2m and 70cm bands. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Let me review the salient observations from the previous work. My question is what is 'higher frequency' specifically? I particularly want to know how counterpoise affects the common mode currents on the coax. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. There are two aspects, however that we need to consider: Lets begin with the transformer. The results are shown below. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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 . A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF 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. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. Above is a thermograph of the transformer at 20W input at 3.6MHz. 2 0 obj Why had I not noticed this before? Does your station desperately need a good RF ground to behave properly? 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 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Finally the tank circuits specification is complete, which is sown below. blue: 250pF, to much compensation. The antenna is effective and the materials and construction are of a very high quality. 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. A 100pF silvered mica was connected in shunt with the transformer primary. You can see the coil in the picture below (red arrow). 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. Basically, the loading coil is operating as a trap. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Some website features may not function optimally without cookies. A 100pF silvered mica was connected in shunt with the transformer . I used the 14g enameled wire and wound it on the FT240-43. Instead, this shifts everything down and makes it very easy to tune 10m. 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. 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. This article will not address that antenna type. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Subscribe to our newsletter and receive regular updates on new posts and articles. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. The worse SWR was 1:1.7 at the top end of 20 meters. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 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. The highest frequency could be14.350MHz. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. This is perhaps one of the most hotly debated rookie topics in. 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. Change), You are commenting using your Twitter account. Can a diode be used to rectify signals smaller than its threshold voltage? Trapped five band EFHW SOTA antenna. So I built myself an improved replacement matching transformer. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. It is worth experimenting with its length also. 100W on a Wire Antenna - Is it good enough for DX? 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. The real power limit will be core heating. : I see you were able to post your comment now, so I just copied my email answer here for others to see. The technical storage or access that is used exclusively for anonymous statistical purposes. I wish you lots of productive experimentations and successful portable operations. Even at 15W the voltage at the ends may reach 100-200V. 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. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. 100W on a Wire Antenna - How far would it reach? I tossed the line as far up as I could in a tree. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Also find news related to Efhw Compensation Coil Experiment which is trending today. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Of course, you will need to find your tuning positions and apply your own position scale. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. . 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. How far could it possibly reach? In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. The wire as I strung it up seemed to resist having a good SWR for the 20m band. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. The impedance matching circuit is essentially a simple parallel resonant LC circuit. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 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 highest voltages as well as radiation are also at the end of the antenna wire. Wrap the first wire around the toroid 27 times (I used a black wire for this). The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. End-Fed antennas are useful in many ways, includes easier mounting of cable at one end (freeing the antenna from unnecessary weight of cable) & antenna maintenance in future. nanoVNA-H can firmware be updated if it has a broken USB socket? Refurbishing aluminium antenna parts affected by weather / corrosion. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Thirty turns #28 are wound on the two FT114-43 cores. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The photos above show a method that works fairly well. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Compensation. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. How does this SWR meter works? 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 antenna is effective and the materials and construction are of a very high quality. See the table above. . The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet.
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