'Capacitor flattens SWR at higher frequencies' - WA7ARK. 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. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. What kind of balun is this? Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Can you give me an idea for your 100 W version, you built for 80/60/40 m. How big and where to place it is likely best determined empirically. <> 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. Above, 3t on the primary delivers Gcore<0.002S. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. AC Coil Replacement Cost 2023 - Forbes Home The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). stream One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. I settled on a compact secondary using #28 wire. 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. One possible explanation is that the core losses drop with temperature. 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 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. The overlaid VSWR plots are shown below. 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. 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%. Instead, this shifts everything down and makes it very easy to tune 10m. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Below about 7 MHz, transmission losses increase as the core temperature increases. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Check your inbox or spam folder to confirm your subscription. 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 antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The combination of the transformer with the end-fed dipole results in a positive reactance. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. We do not know what the actual impedance will be at the end of the antenna radiator. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The parasitic reactances near the feed-point also vary between installations. 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. Low SSN Why do most Hams find HF Radio so difficult? 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? Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Thanks again Jim. It is worth experimenting with its length also. 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. My favorite SOTA antenna is the End-Fed Half Wave Antenna. I particularly want to know how counterpoise affects the common mode currents on the coax. Just the bare 80m wire is shown in red. With such a switch, it is impossible to forget to switch back to operational mode. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I was curious why this capacitor was added to the transformer. It will present its parameters, so anybody with basic home-brew skills will be able to build it. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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 in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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'. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Im very happy with the result. The 40-10m EFHW camping antenna is late but done. More info in - reddit In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. To be safe, better not get much above 120 C. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. 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. A 100pF silvered mica was connected in shunt with the transformer primary. These dimensions were derived from modelling the antenna in EZNEC. 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. 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. How to get started on ISS Cross band Repeater? Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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. My End-Fed Half-Wave (EFHW) AmateurRadio.com I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. EFHW 80m extension - MI0KXX application of Kirchhoff's current Law on a typical EFHW antenna configuration. 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 decided to play with this to see what I could accomplish. The final turns ratio turned out to be 3:29. Now I just need to build or acquire a decent radio to utilize this new antenna. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. The overall lenght is only 15m. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The model results show the need for a not entirely insignificant counterpoise. Most of the time 5 to 20W will be adequate for activation anyway. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. With no counterpoise wire it will be the coaxs shield providing it. What are the advantages and disadvantages of the end-fed half wave antenna? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Look at the compensation coil slide. It is not necessary to calculate the above; the results are sown in the following table. This is typically a weak spot. 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. Elnzst krnk, de elsikkadt az zenete. 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. See the second completed tuner depicted below. We need to measure the inductances of the toroid with the tapped coil. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. Thank you for an interesting and informative read. Basu Bhattacharya (VU2NSB). I decided to push for best efficiency with a 5-turn primary. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. We use cookies to optimize our website and our service. The transformer fits sideways in the box with a few millimeters to spare. 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. Why had I not noticed this before? High Q, hence low loss. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en.