I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. One point of my small-core, compact winding design was to be able to cool the core. There are two aspects, however that we need to consider: Lets begin with the transformer. 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. 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. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. Simulating the end-fed half-wave (EFHW) dipole antenna See the table above. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. This can then, fed with coaxial cable, in many cases be . 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. The worse SWR was 1:1.7 at the top end of 20 meters. 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 think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. It depends on the selection of the inductance and the capacitor values. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. Do I count the six loops around the pvc in the measurement? The End-Fed Half Wave Antenna a bit Differently I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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. The previous table already contains these measurements. Frank VK1VK. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. Check your inbox or spam folder to confirm your subscription. Thank you for an interesting and informative read. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Finally the tank circuits specification is complete, which is sown below. I use shock cord to connect the insulator at the end of the wire to my fence. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The 2 coils are 35uh and 90uh. Instead, this shifts everything down and makes it very easy to tune 10m. Why had I not noticed this before? 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 equation in the article is corrected now. 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" I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? How badly can high Local Ambient QRM affect HF Radio? Above, 3t on the primary delivers Gcore<0.002S. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. <> 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. application of Kirchhoff's current Law on a typical EFHW antenna configuration. 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. stream It is hard to wait an infinitely long time for the box to equilibrate to a given power level. It is important to consider the voltages on this tank circuit. 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. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. There is lot of controversy around the EFHW antennas. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. 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. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. In his article, I will try to bust some of the myths associated with Inverted. 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. How big and where to place it is likely best determined empirically. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. This antenna is only 15m long using 2 loading coils. With such a switch, it is impossible to forget to switch back to operational mode. The overlaid VSWR plots are shown below. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. The parasitic reactances near the feed-point also vary between installations. Below is the schematic of the final build. 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. end fed half wave antenna - awsh.org Efhw Compensation Coil Experiment - Local Search Denver Post A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF Zin=46.52+j6.72. The antenna is up. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! This provides proper insulation from the relatively high voltages on the seconder winding. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Thanks again Jim. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. coil inductance calculator at 66pacific.com. 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. Your article was well written and very informative, thanks. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. It is worth experimenting with its length also. 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 not necessary to calculate the above; the results are sown in the following table. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. . 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 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. It may be one or even five kilo-ohms. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. EFHW Antenna Frequency Compensation Lead - YouTube The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Z8Vq9_@x C\Agv#. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. I checked the wall brackets and mast, but all the fixings were nice and tight. 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 blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. IIRC they call it a "compensator". In theory, the examination is supposed to be used to help clarify your medical condition and . So the differences I see in the data sheets hysteresis curves are not the correct explanation. View the job description, responsibilities and qualifications for this position. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? Many people use an inductor placed at the near end to make things level out on the higher bands. % 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. 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. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Software Engineer - EDI - salary.com An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. And of course, a counterpoise with various lengths. Hello, a wonderful approach for the problems.. It is all about getting the heat out. 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. 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. 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'. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. For . 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. Note: If we change the primary number of turns, the impedance ratios will considerable change also. I decided to play with this to see what I could accomplish. MyAntennas.com Group | When I'm measuring the half way point on my EFHW Im very pleased with that indeed. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. 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. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. 2015. This gave me an effective coil diameter of 40.5mm. Contact Commercial Coils Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. This is typically a weak spot. . A Smith chart view of EFHW transformer compensation . Graphed with a log scale, it makes a nice straight line. %PDF-1.4 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! Does your station desperately need a good RF ground to behave properly? Can a diode be used to rectify signals smaller than its threshold voltage?

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