The following is the most up-to-date information related to EFHW Compensation Coil Experiment. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. Many people use an inductor placed at the near end to make things level out on the higher bands. Transmitting on 15 meters was impossible because of RF into the radio. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. . 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Below about 7 MHz, transmission losses increase as the core temperature increases. Which begs the question what happens when you attach the antenna? 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. One point of my small-core, compact winding design was to be able to cool the core. Finally the tank circuits specification is complete, which is sown below. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Thanks! I will publish my findings, but I cannot not promise to complete it until early fall. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. But systems that work better increase the prospects of contacts. 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. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. A 100pF silvered mica was connected in shunt with the transformer . One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 2. This reveals we only need to compensate for the reactive component. The computation method is also touched on. 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. 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. There are many good descriptions on the net about this type of antenna. . 73 RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. 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. 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. EFHW Antenna Frequency Compensation Lead - YouTube Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. A radio station is as good or as bad as the antenna it has. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 2 0 obj Let me review the salient observations from the previous work. The results are shown below. PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. I dont have an amplifier, so only need to be able to handle 100W. The highest voltages as well as radiation are also at the end of the antenna wire. The SWR was measured for each of the three antennas across the CW portion of the bands. This provides proper insulation from the relatively high voltages on the seconder winding. 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. Thank you for an interesting and informative read. 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. Regards VE9HAM. So I built myself an improved replacement matching transformer. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 100W on a Wire Antenna How far would it reach? This will also be handling 100W. I wish I had a simple answer, but really this is where some experimentation can pay off. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Looking at several builds and discussions, such as commercial antennas (e.g. Let's find out! It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. 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. 1. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. 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. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Experiments with 160m antennas | VK3IL Blog From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Some hams swear by them, yet some completely demean it. 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 performed well on both the 2m and 70cm bands. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. You can see the coil in the picture below (red arrow). It is not necessary to calculate the above; the results are sown in the following table. For the last step, I put together a RF choke to use between the radio and the feedline. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. As is often the case, packaging was determined by what boxes I had laying around. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. nanoVNA-H can firmware be updated if it has a broken USB socket? 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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. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. If you stare at the above frequency sweeps you will discover a few things. 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. uBITX HF Transceiver Build - My Adventures in Engineering The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). 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. Consequently, this is how the capacitance values are determined. Low SSN Why do most Hams find HF Radio so difficult? End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Could it be something to do with the new vertical aerial I had recently installed? A week or two later I started to notice an occasional knocking sound inside the house. Of course, you will need to find your tuning positions and apply your own position scale. However, a key restriction is its 25W power rating, due to the small matching transformer. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. A 100pF silvered mica was connected in shunt with the transformer primary. This is not an optimal value, benefit may be obtained by exploring small changes to that value. The bridge than will measure zero voltage across the bridge, and the LED will turn off. Some say you do not need a counterpoise, but that is false. Frank VK1VK. 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. 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 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. Thanks in advance, good health for you in these times, Just the bare 80m wire is shown in red. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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. View the job description, responsibilities and qualifications for this position. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. i liked it a lot, you give good ideas, many thanks. This antenna is only 15m long using 2 loading coils. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Why had I not noticed this before? Wrap the first wire around the toroid 27 times (I used a black wire for this). Below is the schematic of the final build. The 40-10m EFHW camping antenna is late but done. More info in - reddit . With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. The final turns ratio turned out to be 3:29. By using traps, the antenna works on all three bands with no operator interaction. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. A week or two later I started to notice an occasional knocking sound inside the house. (LogOut/ Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. And of course, a counterpoise with various lengths. A ktelez mezket * karakterrel jelltk. 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. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. We need to measure the inductances of the toroid with the tapped coil. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. 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. I then added two 220pf capacitors in series between the center conductor and ground. Independent Medical Evaluation - IME | Cynthia Hennessey Isn't it? Consider the RC time for a source with 2500 impedance into a 1pF capacitor. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. 2006. The highest frequency could be14.350MHz. Even at 15W the voltage at the ends may reach 100-200V. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Proudly created withWix.com. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The previous table already contains these measurements. So far so good. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? The SWR figures were as follows: FT240-43 132ft/100pF capacitor My favorite SOTA antenna is the End-Fed Half Wave Antenna. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. 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" 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. The photos above show a method that works fairly well. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. Thanks again Jim. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Im very pleased with that indeed. 73! 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 needed to add an additional coil (approx 12.5 uH) about . And now I am planning to build one for 160/80m. Show more. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. The difference here is that the target bands are low frequency. It is worth experimenting with its length also. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Now I just need to build or acquire a decent radio to utilize this new antenna. Also find news related to Efhw Compensation Coil Experiment which is trending today. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. A Smith chart view of EFHW transformer compensation Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. application of Kirchhoff's current Law on a typical EFHW antenna configuration. 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. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. stream Lowest measured inductivity = 2.0 H. of the wavelength. The band compensating inductor placed on the wire is another story. 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. I was curious why this capacitor was added to the transformer. 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. In this case, it looks important. 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. The model results show the need for a not entirely insignificant counterpoise. 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. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. 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. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. Note: If we change the primary number of turns, the impedance ratios will considerable change also. The resistance (real) component of the impedance is right where we want it near 50 ohms. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. 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. 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. The equation in the article is corrected now. And not all hf antenna installation are same, with most requiring bit of tinkering. Let us touch on some necessary theory to begin with. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 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. The EFHW transformer box from outside. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. I would mention first its ease of installation. One end is about 5 meters high on an extended fishing pole. Lets call this element the LoadAttenuator. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. The technical storage or access that is used exclusively for anonymous statistical purposes. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Best regards and thanks again for your comment. If not a lightning strike, I will write an article about the experience as well. 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. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. I am currently working on measurements of an EFHW antenna. It is recommended to use at least 2W non-inductive resistors for this purpose. Lets do a quick calculation to see how much an issue is this output capacitance. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! IIRC they call it a "compensator". A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. You can start with the links below. In theory, the examination is supposed to be used to help clarify your medical condition and . The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. How big and where to place it is likely best determined empirically. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. I decided to push for best efficiency with a 5-turn primary. High Q, hence low loss. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Software Engineer - EDI - salary.com This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. I used four parallel #28 wires (not twisted) for the primary. It is important to consider the voltages on this tank circuit.

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