I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. 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. 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. This provides proper insulation from the relatively high voltages on the seconder winding. 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'. = .000001 / 3868.88 This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 2006. 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 matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. 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. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Well, in ham radio, everything works. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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. 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. The negative effects of local QRM on an, How does antenna radiation occur? The technical storage or access that is used exclusively for anonymous statistical purposes. However, it has its idiosyncrasies. Graphed with a log scale, it makes a nice straight line. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Wrap the first wire around the toroid 27 times (I used a black wire for this). Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. IIRC they call it a "compensator". Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. I tossed the line as far up as I could in a tree. 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. 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). 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. Some website features may not function optimally without cookies. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. The equation in the article is corrected now. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. And not all hf antenna installation are same, with most requiring bit of tinkering. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Check your inbox or spam folder to confirm your subscription. Krem, rja le, mi a krdse. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Change), You are commenting using your Facebook account. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. I decided to push for best efficiency with a 5-turn primary. It uses a coil as a compensation unit, and no counterpoise. The previous table already contains these measurements. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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. 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. The impedance matching circuit is essentially a simple parallel resonant LC circuit. So, how to construct an end-fed half wave antenna? The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 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. Research salary, company info, career paths, and top skills for Software Engineer - EDI Elnzst krnk, de elsikkadt az zenete. 2 0 obj The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. And now I am planning to build one for 160/80m. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Be sure to take a look for additional analysis and conclusions. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The final turns ratio turned out to be 3:29. I was curious why this capacitor was added to the transformer. Basu Bhattacharya (VU2NSB). Could it be something to do with the new vertical aerial I had recently installed? The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. 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. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Hence, we need to move along and start to include the antenna with our testing. nanoVNA-H can firmware be updated if it has a broken USB socket? 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. 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. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. i liked it a lot, you give good ideas, many thanks. Lowest measured inductivity = 2.0 H. I also will ask, why didnt it work for you. For the last step, I put together a RF choke to use between the radio and the feedline. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. . I installed a QRP SWR meter into the tuner that makes tuning very handy. 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. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. 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. It is recommended to use at least 2W non-inductive resistors for this purpose. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. 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. Thank you for your comment and feedback on the article about the EFHW antenna. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. It not a loading coil. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. I am planning to use this latest one at the Field Day next year. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. 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. 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). PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. The basic question before us is how does an antenna work? Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! 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. = .00 00 00 00 0 258 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. 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. Above is a sweep of the roughly compensated transformer. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 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. The transformer fits sideways in the box with a few millimeters to spare. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. ROB@COMCOIL.COM 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. Be aware counterpoise or ground radials are required for all hf antennas for better performance. This reveals we only need to compensate for the reactive component. This is not an optimal value, benefit may be obtained by exploring small changes to that value. How big and where to place it is likely best determined empirically. Cmzett: Weince joseph How can we help? Most of the time 5 to 20W will be adequate for activation anyway. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Understanding Antennas The Good, the Bad, and the Ugly. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. From that we can find Mismatch Loss. The radiation pattern of this antenna on most bands produces multiple lobes. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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. Zin=46.52+j6.72. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. No wire counterpoise is used to reproduce the SOTA setup. 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 graphical depiction makes it easier to visualize the current and impedance correlation between bands. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. That is an end-fed, but very different then the half wave construction. We also need to know what are the frequencies or bands for which we plant to use this antenna. The highest voltages as well as radiation are also at the end of the antenna wire. VSWR<1.8 over all of HF. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. 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. Proudly created withWix.com. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. A week or two later I started to notice an occasional knocking sound inside the house. Consequently, this is how the capacitance values are determined. On the transformer, I added a few wingnuts to tighten down the antenna wire. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. So, I embarked on testing it for myself. (LogOut/ The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Can a diode be used to rectify signals smaller than its threshold voltage? The technical storage or access that is used exclusively for statistical purposes. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. 1. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 5) It is very hard to avoid stray capacitance on the output. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Could it be something to do with the new vertical aerial I had recently installed? 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). 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. This is perhaps one of the most hotly debated rookie topics in. Instead, this shifts everything down and makes it very easy to tune 10m. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. The parasitic reactances near the feed-point also vary between installations. Ismerje meg a hozzszls adatainak feldolgozst . I used four parallel #28 wires (not twisted) for the primary. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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.) 100W on a Wire Antenna - How far would it reach? This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. In an urban area we are much more restricted, especially if we need to be stealth about it. It performed well on both the 2m and 70cm bands. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. 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. A 100pF silvered mica was connected in shunt with the transformer primary. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. To further improve the flux linkage, I wound the primary on top of the secondary. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. blue: 250pF, to much compensation. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. The difference here is that the target bands are low frequency. See the table above. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. I decided to play with this to see what I could accomplish. Subscribe to our newsletter and receive regular updates on new posts and articles. The band compensating inductor placed on the wire is another story. I decided to play with this to see what I could accomplish. Current Balun 1. Best regards and thanks again for your comment. Many people use an inductor placed at the near end to make things level out on the higher bands. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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.
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