I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Cmzett: Weince joseph How can we help? 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. Basu Bhattacharya (VU2NSB). On the transformer, I added a few wingnuts to tighten down the antenna wire. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Some website features may not function optimally without cookies. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. Be sure to take a look for additional analysis and conclusions. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. The original coil is designed for low power portable applications. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. You cant really see the antenna wire, but the red line shows the antenna path. It is worth experimenting with its length also. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Do I count the six loops around the pvc in the measurement? And now I am planning to build one for 160/80m. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. There are two aspects, however that we need to consider: Lets begin with the transformer. Copyright 2014-2023. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. However, it has its idiosyncrasies. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 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.) Klubunknl folyamatos a tagfelvtel. Interpretation of S-Meter Noise Floor in HF Radio Receivers. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Elnzst krnk, de elsikkadt az zenete. For . However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 5) It is very hard to avoid stray capacitance on the output. 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. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. How to get started on ISS Cross band Repeater? With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. The wire as I strung it up seemed to resist having a good SWR for the 20m band. Hence, we need to move along and start to include the antenna with our testing. 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. 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 permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. So I built myself an improved replacement matching transformer. 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. 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. The impedance matching circuit is essentially a simple parallel resonant LC circuit. 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. Contact Commercial Coils If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. The highest voltages as well as radiation are also at the end of the antenna wire. Frank VK1VK. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. Could it be something to do with the new vertical aerial I had recently installed? However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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. 2. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Lets call this element the LoadAttenuator. Lowest frequency = 7.000 MHz. Hello, a wonderful approach for the problems.. clear. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. How badly can high Local Ambient QRM affect HF Radio? . 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. The combination of the transformer with the end-fed dipole results in a positive reactance. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. Hence, there is no optimum single-fit solution. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. In theory, the examination is supposed to be used to help clarify your medical condition and . 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. 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Above is a sweep of the roughly compensated transformer. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. 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. This can then, fed with coaxial cable, in many cases be . It is quite possible that designing more than three or four bands into a tuner will lead to a failure. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. High self-resonant frequency. Highest frequency = 14.350 MHz. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite Look at the compensation coil slide. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. They will be adjusted for resonance at or close to the CW portion of the bands. But I would caution its usage for higher power than 10-15W. I tossed the line as far up as I could in a tree. The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. 100W on a Wire Antenna - How far would it reach? 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. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 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'. stream Zin=46.52+j6.72. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. The End-Fed Half Wave Antenna a bit Differently With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. : I see you were able to post your comment now, so I just copied my email answer here for others to see. This gave me an effective coil diameter of 40.5mm. Will there be the same performance for single band EFHWs? Most informative and appreciated. 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. 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. 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. How does this SWR meter works? The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. So, how to construct an end-fed half wave antenna? I assume you know the GNARC source for EFHW antennas. I decided to push for best efficiency with a 5-turn primary. Check your inbox or spam folder to confirm your subscription. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Compensation. No capacitor was installed. I used four parallel #28 wires (not twisted) for the primary. It requires a set distance to hang both ends of the antenna, and that is not always given. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. ON7EQ EFHW Antenna - qsl.net 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. Thank you for your comment and feedback on the article about the EFHW antenna. This is perhaps one of the most hotly debated rookie topics in. 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. (LogOut/ 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. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Isn't it? The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Could it be something to do with the new vertical aerial I had recently installed? In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. %PDF-1.4 That will be the missing resistor in the resistor bridge of the below circuit. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. Change). The antenna is up. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. I mounted the transformer on a tree for testing. This suggests an inductive reactance. The original coil is designed for low power portable applications. The EFHW transformer box from outside. EFHW Compensation Coil Experiment - YouTube 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. coil inductance calculator at 66pacific.com. 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. It performed well on both the 2m and 70cm bands. The real power limit will be core heating. A week or two later I started to notice an occasional knocking sound inside the house. 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. My favorite SOTA antenna is the End-Fed Half Wave Antenna. The SWR for the 20 meter EFHW antenna was < 1.2:1 One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? 100W on a Wire Antenna How far would it reach? The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. Can a diode be used to rectify signals smaller than its threshold voltage? Your posting put it all together for meTHANK YOU!!!! Which begs the question what happens when you attach the antenna? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. My End-Fed Half-Wave (EFHW) AmateurRadio.com 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. 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. I am building an EFHW antenna for my new. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. 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%. Graphed with a log scale, it makes a nice straight line. 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 100W on a Wire Antenna - Is it good enough for DX? This provides proper insulation from the relatively high voltages on the seconder winding. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties.