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. My End-Fed Half-Wave (EFHW) AmateurRadio.com 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. EFHW Compensation Coil Experiment - YouTube Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 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. Next, I started winding the transformer. Hi Ajai, 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. You can start with the links below. That will be the missing resistor in the resistor bridge of the below circuit. 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. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. Some website features may not function optimally without cookies. 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. The overlaid VSWR plots are shown below. The wire as I strung it up seemed to resist having a good SWR for the 20m band. Elnzst krnk, de elsikkadt az zenete. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. The equation should have a 10^6 and not 10^-6 in the nominator. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. My question is what is 'higher frequency' specifically? Finally the tank circuits specification is complete, which is sown below. 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. Cmzett: Weince joseph How can we help? The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. 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. So, how to construct an end-fed half wave antenna? EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com If not a lightning strike, I will write an article about the experience as well. Thank you for an interesting and informative read. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. I tossed the line as far up as I could in a tree. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The parasitic reactances near the feed-point also vary between installations. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. 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. I then added two 220pf capacitors in series between the center conductor and ground. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Hence, there is no optimum single-fit solution. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. What are its disadvantages? There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Be sure to take a look for additional analysis and conclusions. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency The technical storage or access that is used exclusively for statistical purposes. However, a key restriction is its 25W power rating, due to the small matching transformer. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. It is important to consider the voltages on this tank circuit. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. In this case, it looks important. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. To further improve the flux linkage, I wound the primary on top of the secondary. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Even at 15W the voltage at the ends may reach 100-200V. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. Why does antenna radiation occur? Current Balun 1. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. The original coil is designed for low power portable applications. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF (LogOut/ 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube Krem, rja le, mi a krdse. Below is the schematic of the final build. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. The End-Fed Half Wave Antenna a bit Differently However, it has its idiosyncrasies. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. 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. Thanks! Which begs the question what happens when you attach the antenna? Trapped five band EFHW SOTA antenna. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. 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. 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. 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 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'. 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 strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. Highest frequency = 14.350 MHz. 5) It is very hard to avoid stray capacitance on the output. If you stare at the above frequency sweeps you will discover a few things. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Check your inbox or spam folder to confirm your subscription. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Above 7MHz, there is very little temperature dependence at all. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. Basically, the loading coil is operating as a trap. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. 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. 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. The resistance (real) component of the impedance is right where we want it near 50 ohms. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. 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). 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. I am building an EFHW antenna for my new. This gave me an effective coil diameter of 40.5mm. Hello, a wonderful approach for the problems.. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex There are many good descriptions on the net about this type of antenna. How does this SWR meter works? A Smith chart view of EFHW transformer compensation Start by wrapping the wire around the toroid. 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. 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. 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. The band compensating inductor placed on the wire is another story. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. In an urban area we are much more restricted, especially if we need to be stealth about it. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. One way or another there is always a counterpoise involved if the antenna is tuned correctly. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. It performed well on both the 2m and 70cm bands. 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. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Most of the time 5 to 20W will be adequate for activation anyway. VK1OD.net (offline). I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. 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. They will be adjusted for resonance at or close to the CW portion of the bands. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. This is typically a weak spot. I was curious why this capacitor was added to the transformer. 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. Contact Commercial Coils Jim, do you mind if I add your email and my answer as a comment to the article? The computation method is also touched on. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. Very interesting design. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Show more. Lets do a quick calculation to see how much an issue is this output capacitance. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. : I see you were able to post your comment now, so I just copied my email answer here for others to see. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. No capacitor was installed. 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. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. It is best to make the impedance matching adjustable, using switched transformation ratio. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. uBITX HF Transceiver Build - My Adventures in Engineering Frank VK1VK. Looking at several builds and discussions, such as commercial antennas (e.g. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. One possible explanation is that the core losses drop with temperature. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Above, 3t on the primary delivers Gcore<0.002S. This article will not address that antenna type. The difference here is that the target bands are low frequency. 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. 1. If you really want to get the heat out, add some fins to the aluminum box. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. We do not know what the actual impedance will be at the end of the antenna radiator. The antenna is effective and the materials and construction are of a very high quality. (LogOut/ Hence, we need to move along and start to include the antenna with our testing. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. 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. Lets call this element the LoadAttenuator. 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. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. So far so good. Thirty turns #28 are wound on the two FT114-43 cores. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 2 0 obj Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The combination of the transformer with the end-fed dipole results in a positive reactance. I dont have an amplifier, so only need to be able to handle 100W. A short 80m antenna for my lot - KB6NU's Ham Radio Blog <> The transformer fits sideways in the box with a few millimeters to spare. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Most informative and appreciated. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Low SSN Why do most Hams find HF Radio so difficult? So, I embarked on testing it for myself. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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. Be cautious, such voltages may cause a quite painful skin scorch. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Why had I not noticed this before? 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. This will yield the maximum capacity of the variable capacitor. Pocket-tenna core is finally done! Wire and compensation coil being . There is lot of controversy around the EFHW antennas. Can you give me an idea for your 100 W version, you built for 80/60/40 m. There is much more that can be written about this antenna and its matching, but that was not my aim. It is recommended to use at least 2W non-inductive resistors for this purpose. The worse SWR was 1:1.7 at the top end of 20 meters. View the job description, responsibilities and qualifications for this position. VSWR<1.8 over all of HF. 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. = 258 * 10^-12. It is all about getting the heat out. % The highest voltages as well as radiation are also at the end of the antenna wire. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. |k"^N>F.AnJkJsq'PV}o0I. More designs can be found by Googling "80m loaded dipole.". Csatlakozz csapatunkhoz! That is an end-fed, but very different then the half wave construction. This is perhaps one of the most hotly debated rookie topics in. Refurbishing aluminium antenna parts affected by weather / corrosion. Make sure the first wire is wrapped evenly around the whole toroid. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The highest frequency could be14.350MHz. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. This reveals we only need to compensate for the reactive component. . As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 73 It may be one or even five kilo-ohms. 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. 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. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. Is FT8 popularity growing at the cost of SSB Phone and CW? 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 decided to push for best efficiency with a 5-turn primary. 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. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. I found it very useful to label the tuner with switch and capacitance positions. 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. I decided to play with this to see what I could accomplish. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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.) I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. The antenna is up. Trapped five band EFHW SOTA antenna | VK3IL Blog
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