Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . Lowest measured inductivity = 2.0 H. The technical storage or access that is used exclusively for statistical purposes. Basu Bhattacharya (VU2NSB). Some say you do not need a counterpoise, but that is false. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. The next important parameter is the parallel resonant circuits resonant frequency. Impressive article and so well done that I may give it a try. So I built myself an improved replacement matching transformer. But systems that work better increase the prospects of contacts. 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. 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. So, I embarked on testing it for myself. Highest frequency = 14.350 MHz. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. Basically, the loading coil is operating as a trap. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. Instead, this shifts everything down and makes it very easy to tune 10m. Thank you for your comment and feedback on the article about the EFHW antenna. Above is a sweep of the roughly compensated transformer. Lets do a quick calculation to see how much an issue is this output capacitance. 73 In his article, I will try to bust some of the myths associated with Inverted. It should be no surprise that 80pF is close to optimal. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. Compensation. 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. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. A radio station is as good or as bad as the antenna it has. The toroid with its many taps may be soldered directly on a multi-position switch. 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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'. A ktelez mezket * karakterrel jelltk. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 2006. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. This will yield the maximum capacity of the variable capacitor. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. Interpretation of S-Meter Noise Floor in HF Radio Receivers. After some internet research, I settled on making the former from a paint roller. I installed a QRP SWR meter into the tuner that makes tuning very handy. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. = 1/30.e6 = 33 nS. 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. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Wow, Gary! Let's find out! I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Even at 15W the voltage at the ends may reach 100-200V. That is an end-fed, but very different then the half wave construction. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. Thirty turns #28 are wound on the two FT114-43 cores. Isn't it? Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. 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. I will go back and have the article corrected. 100W on a Wire Antenna - How far would it reach? Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. Current Balun 1. 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. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. However, a key restriction is its 25W power rating, due to the small matching transformer. On the transformer, I added a few wingnuts to tighten down the antenna wire. This provides proper insulation from the relatively high voltages on the seconder winding. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The computation method is also touched on. So far so good. 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. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. The resistance (real) component of the impedance is right where we want it near 50 ohms. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. coil inductance calculator at 66pacific.com. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 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. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. : I see you were able to post your comment now, so I just copied my email answer here for others to see. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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? View the job description, responsibilities and qualifications for this position. 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. Which begs the question what happens when you attach the antenna? 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. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. The combination of the transformer with the end-fed dipole results in a positive reactance. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. 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. 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. As is often the case, packaging was determined by what boxes I had laying around. This reveals we only need to compensate for the reactive component. Could it be something to do with the new vertical aerial I had recently installed? Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. This is not an optimal value, benefit may be obtained by exploring small changes to that value. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. This will also be handling 100W. Nagyon j ez a cikk. 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. I particularly want to know how counterpoise affects the common mode currents on the coax. Thanks for your comments. Refurbishing aluminium antenna parts affected by weather / corrosion. Copyright 2014-2023. <> 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. They will be adjusted for resonance at or close to the CW portion of the bands. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. Thanks in advance, good health for you in these times, And now I am planning to build one for 160/80m. Some hams swear by them, yet some completely demean it. Be cautious, such voltages may cause a quite painful skin scorch. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. The results are shown below. Z8Vq9_@x C\Agv#. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Do I count the six loops around the pvc in the measurement? 1. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. With no counterpoise wire it will be the coaxs shield providing it. 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. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands.