We use cookies to optimize our website and our service. The original coil is designed for low power portable applications. This can then, fed with coaxial cable, in many cases be . = 258 * 10^-12. Trapped five band EFHW SOTA antenna. = .000001 / 3868.88 The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. The parasitic reactances near the feed-point also vary between installations. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 2 0 obj Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. Transmitting on 15 meters was impossible because of RF into the radio. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. For . 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. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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. I found it very useful to label the tuner with switch and capacitance positions. blue: 250pF, to much compensation. If you stare at the above frequency sweeps you will discover a few things. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. This will yield the maximum capacity of the variable capacitor. To further improve the flux linkage, I wound the primary on top of the secondary. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. Proudly created withWix.com. Thanks in advance, good health for you in these times, It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. 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. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. Above is a sweep of the uncompensated prototype with a 3220+50 load. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. I used four parallel #28 wires (not twisted) for the primary. 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. Isn't it? 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. I checked the wall brackets and mast, but all the fixings were nice and tight. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. 2015. See the second completed tuner depicted below. 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. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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(The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I will go back and have the article corrected. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Even at 15W the voltage at the ends may reach 100-200V. We do not know what the actual impedance will be at the end of the antenna radiator. Check your inbox or spam folder to confirm your subscription. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. If not a lightning strike, I will write an article about the experience as well. Im very pleased with that indeed. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . Let's find out! We also need to know what are the frequencies or bands for which we plant to use this antenna. In this case, it looks important. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. <> Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. It performed well on both the 2m and 70cm bands. i liked it a lot, you give good ideas, many thanks. There is much more that can be written about this antenna and its matching, but that was not my aim. Nagyon j ez a cikk. % The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Very interesting design. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. I then used a piece of heat shrink on the outside to hold everything in place. I assume you know the GNARC source for EFHW antennas. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. 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. Jim, do you mind if I add your email and my answer as a comment to the article? With such a switch, it is impossible to forget to switch back to operational mode. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Below is the schematic of the final build. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. Im very happy with the result. 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. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. 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. My question is what is 'higher frequency' specifically? The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. If you really want to get the heat out, add some fins to the aluminum box. I will publish my findings, but I cannot not promise to complete it until early fall. Will there be the same performance for single band EFHWs? I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. Does your station desperately need a good RF ground to behave properly? How big and where to place it is likely best determined empirically. 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 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. : I see you were able to post your comment now, so I just copied my email answer here for others to see. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" What are its disadvantages? 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. 100W on a Wire Antenna - Is it good enough for DX? A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 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. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. The difference here is that the target bands are low frequency. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. At this point, I'm leaning towards the EFHW, but any of these antennas seem . The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). It depends on the selection of the inductance and the capacitor values. 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. Elnzst krnk, de elsikkadt az zenete. The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. 5) It is very hard to avoid stray capacitance on the output. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. Hence, there is no optimum single-fit solution. So the differences I see in the data sheets hysteresis curves are not the correct explanation. I then added two 220pf capacitors in series between the center conductor and ground. Frank VK1VK. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. The transformer fits sideways in the box with a few millimeters to spare. Be cautious, such voltages may cause a quite painful skin scorch. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 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 will present its parameters, so anybody with basic home-brew skills will be able to build it. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. How to get started on ISS Cross band Repeater? Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The SWR for the 20 meter EFHW antenna was < 1.2:1 See the table above. This will yield the minimal capacitance of the variable capacitor. 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. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. 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. 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). If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Regards VE9HAM. Look at the compensation coil slide. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. There are two aspects, however that we need to consider: Lets begin with the transformer. . 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. 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 technical storage or access that is used exclusively for anonymous statistical purposes. It uses a coil as a compensation unit, and no counterpoise. Could it be something to do with the new vertical aerial I had recently installed? 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. There are many good descriptions on the net about this type of antenna. It is important to consider the voltages on this tank circuit. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. I added some Christmas colored zip ties to hold everything in place. Note: If we change the primary number of turns, the impedance ratios will considerable change also. However, it has its idiosyncrasies. 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.) 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. The SWR figures were as follows: FT240-43 132ft/100pF capacitor (LogOut/ 73! 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. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. The bridge than will measure zero voltage across the bridge, and the LED will turn off. 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. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Above, 3t on the primary delivers Gcore<0.002S. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Well, in ham radio, everything works. The equation should have a 10^6 and not 10^-6 in the nominator. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. 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. The overlaid VSWR plots are shown below. Klubunknl folyamatos a tagfelvtel. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. Of course, you will need to find your tuning positions and apply your own position scale. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. 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. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. The previous table already contains these measurements. Is it any good? No wire counterpoise is used to reproduce the SOTA setup. And not all hf antenna installation are same, with most requiring bit of tinkering. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. I decided to play with this to see what I could accomplish. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). . I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. 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. Some website features may not function optimally without cookies. 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. 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. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. That will be the missing resistor in the resistor bridge of the below circuit. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. 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. It does not need any special components; in fact, most of us may have them in our shack drawers already. The combination of the transformer with the end-fed dipole results in a positive reactance. And now I am planning to build one for 160/80m. 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. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. Most of the time 5 to 20W will be adequate for activation anyway.