Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The technical storage or access that is used exclusively for statistical purposes. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. %PDF-1.4 The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. See the second completed tuner depicted below. 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. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. Why does antenna radiation occur? Finally the tank circuits specification is complete, which is sown below. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. A week or two later I started to notice an occasional knocking sound inside the house. As is often the case, packaging was determined by what boxes I had laying around. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. Basically, the loading coil is operating as a trap. It is important that resonance may be achieved at each tap of the inductance. 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. I also will ask, why didnt it work for you. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The antenna is effective and the materials and construction are of a very high quality. I then added two 220pf capacitors in series between the center conductor and ground. Zin=46.52+j6.72. |k"^N>F.AnJkJsq'PV}o0I. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Trapped five band EFHW SOTA antenna. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. 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 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. 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. 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. Graphed with a log scale, it makes a nice straight line. nanoVNA-H can firmware be updated if it has a broken USB socket? I checked the wall brackets and mast, but all the fixings were nice and tight. 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. = 1/30.e6 = 33 nS. Current Balun 1. As I reexamined my formula, you pointed it out correctly, there is an error in it. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. There are two aspects, however that we need to consider: Lets begin with the transformer. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. The equation should have a 10^6 and not 10^-6 in the nominator. Krem, rja le, mi a krdse. By using traps, the antenna works on all three bands with no operator interaction. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). The highest frequency could be14.350MHz. 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. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Could it be something to do with the new vertical aerial I had recently installed? Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. . 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. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. This is not an optimal value, benefit may be obtained by exploring small changes to that value. The original coil is designed for low power portable applications. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. There is lot of controversy around the EFHW antennas. No wire counterpoise is used to reproduce the SOTA setup. The EFHW transformer box from outside. I use shock cord to connect the insulator at the end of the wire to my fence. The coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. Above, 3t on the primary delivers Gcore<0.002S. The 2 coils are 35uh and 90uh. 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. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. It is recommended to use at least 2W non-inductive resistors for this purpose. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. 1. I found it very useful to label the tuner with switch and capacitance positions. What are the advantages and disadvantages of the end-fed half wave antenna? There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. Then I covered the coil in kapton tape to hold it together. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Start by wrapping the wire around the toroid. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. It is not necessary to calculate the above; the results are sown in the following table. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. This gave me an effective coil diameter of 40.5mm. Regards VE9HAM. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. The antennas are set up as a sloper as in my SOTA outings. Thanks in advance, good health for you in these times, Elnzst krnk, de elsikkadt az zenete. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The transformer fits sideways in the box with a few millimeters to spare. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. I particularly want to know how counterpoise affects the common mode currents on the coax. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. It does not need any special components; in fact, most of us may have them in our shack drawers already. What are its disadvantages? So I built myself an improved replacement matching transformer. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. To further improve the flux linkage, I wound the primary on top of the secondary. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. 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. I needed to add an additional coil (approx 12.5 uH) about . We do not know what the actual impedance will be at the end of the antenna radiator. 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. But I would caution its usage for higher power than 10-15W. Now I just need to build or acquire a decent radio to utilize this new antenna. 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. 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 a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. 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. Which begs the question what happens when you attach the antenna? This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. Note: If we change the primary number of turns, the impedance ratios will considerable change also. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. All Rights Reserved. Low SSN Why do most Hams find HF Radio so difficult? 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. For the last step, I put together a RF choke to use between the radio and the feedline. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. The biggest uncertainty in these measurements was the actual power level used. Refurbishing aluminium antenna parts affected by weather / corrosion. Why had I not noticed this before? However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings.