Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. Above is a sweep of the uncompensated prototype with a 3220+50 load. The transformer fits sideways in the box with a few millimeters to spare. 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). PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. EFHW 80m extension - MI0KXX After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. (LogOut/ Research salary, company info, career paths, and top skills for Software Engineer - EDI Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. After some internet research, I settled on making the former from a paint roller. 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. 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. nanoVNA-H can firmware be updated if it has a broken USB socket? The final turns ratio turned out to be 3:29. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? They will be adjusted for resonance at or close to the CW portion of the bands. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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. EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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 antennas are set up as a sloper as in my SOTA outings. Efhw Compensation Coil Experiment - Local Search Denver Post Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. 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. This article will not address that antenna type. Simulating the end-fed half-wave (EFHW) dipole antenna This is not an optimal value, benefit may be obtained by exploring small changes to that value. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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. . RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Frank VK1VK. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Above 7MHz, there is very little temperature dependence at all. Proudly created withWix.com. The real power limit will be core heating. 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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. 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. 2. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. Change), You are commenting using your Twitter account. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube Apply for the Job in Software Engineer - EDI at St. Louis, MO. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. 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. 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. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 5) It is very hard to avoid stray capacitance on the output. Some website features may not function optimally without cookies. 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. 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 transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. of the wavelength. 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. Most informative and appreciated. 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 . I was curious why this capacitor was added to the transformer. In theory, the examination is supposed to be used to help clarify your medical condition and . This reveals we only need to compensate for the reactive component. 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 was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com If not a lightning strike, I will write an article about the experience as well. 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. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. One point of my small-core, compact winding design was to be able to cool the core. Transmitting on 15 meters was impossible because of RF into the radio. application of Kirchhoff's current Law on a typical EFHW antenna configuration. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. 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). inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. One end is about 5 meters high on an extended fishing pole. <> 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. Low SSN Why do most Hams find HF Radio so difficult? We also need to know what are the frequencies or bands for which we plant to use this antenna. MyAntennas.com Group | When I'm measuring the half way point on my EFHW Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. 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. I installed a QRP SWR meter into the tuner that makes tuning very handy. Impressive article and so well done that I may give it a try. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. You cant really see the antenna wire, but the red line shows the antenna path. Be cautious, such voltages may cause a quite painful skin scorch. 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. Hence, we need to move along and start to include the antenna with our testing. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. That will be the missing resistor in the resistor bridge of the below circuit. 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. A short 80m antenna for my lot - KB6NU's Ham Radio Blog Graphed with a log scale, it makes a nice straight line. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Make sure the first wire is wrapped evenly around the whole toroid. 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. More designs can be found by Googling "80m loaded dipole.". 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil It may be one or even five kilo-ohms. This will yield the maximum capacity of the variable capacitor. Subscribe to our newsletter and receive regular updates on new posts and articles. 2 0 obj It depends on the selection of the inductance and the capacitor values. I will go back and have the article corrected. 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. I ran WSPR at 10mW for about 2 hours and got the results below. PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). It requires a set distance to hang both ends of the antenna, and that is not always given. 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? From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? The combination of the transformer with the end-fed dipole results in a positive reactance. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. The previous table already contains these measurements. 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. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Even at 15W the voltage at the ends may reach 100-200V. EFHW Antenna Frequency Compensation Lead - YouTube Generally a loading coil has far more inductance and shortens the length of the antenna significantly. The overall lenght is only 15m. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. Instead, this shifts everything down and makes it very easy to tune 10m. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The model results show the need for a not entirely insignificant counterpoise. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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'. . The final turns ratio turned out to be 3:29. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Trapped five band EFHW SOTA antenna. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 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. end fed half wave antenna - awsh.org With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. 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. Be aware counterpoise or ground radials are required for all hf antennas for better performance. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. Could it be something to do with the new vertical aerial I had recently installed? 100W on a Wire Antenna - Is it good enough for DX? 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. The negative effects of local QRM on an, How does antenna radiation occur? 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. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. I decided to push for best efficiency with a 5-turn primary. Hi Ajai, The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. One possible explanation is that the core losses drop with temperature. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. (LogOut/ High self-resonant frequency. 100W on a Wire antenna! = 1/30.e6 = 33 nS. There is much more that can be written about this antenna and its matching, but that was not my aim. This suggests an inductive reactance. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. I wish you lots of productive experimentations and successful portable operations. It is worth experimenting with its length also. A week or two later I started to notice an occasional knocking sound inside the house.
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