After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The difference here is that the target bands are low frequency. . Lowest frequency = 7.000 MHz. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. And now I am planning to build one for 160/80m. Isn't it? 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. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. By using traps, the antenna works on all three bands with no operator interaction. The resistance (real) component of the impedance is right where we want it near 50 ohms. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Impressive article and so well done that I may give it a try. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Lowest measured inductivity = 2.0 H. 2015. A ktelez mezket * karakterrel jelltk. Change), You are commenting using your Twitter account. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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 . 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. If you stare at the above frequency sweeps you will discover a few things. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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. The antenna is up. This can then, fed with coaxial cable, in many cases be . 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. It requires a set distance to hang both ends of the antenna, and that is not always given. Proudly created withWix.com. Hi Ajai, It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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 low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap 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. 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. Thank you Gary. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. 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. The Counterpoise is a short, typically one twentieth (0.05 *. ) 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 checked the wall brackets and mast, but all the fixings were nice and tight. The equation in the article is corrected now. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. How badly can high Local Ambient QRM affect HF Radio? An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Also find news related to Efhw Compensation Coil Experiment which is trending today. Below is the schematic of the final build. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. For a quarter wave that is about 8 nS. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. 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. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. The highest frequency could be14.350MHz. It depends on the selection of the inductance and the capacitor values. I then added two 220pf capacitors in series between the center conductor and ground. 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. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. blue: 250pF, to much compensation. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. For . The previous table already contains these measurements. You can see the coil in the picture below (red arrow). 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. Lets call this element the LoadAttenuator. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. 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. 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 condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. In an urban area we are much more restricted, especially if we need to be stealth about it. This antenna is working for 80,40,20,10 and 6m bands. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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). The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 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. 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. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. Research salary, company info, career paths, and top skills for Software Engineer - EDI A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Above is a sweep of the roughly compensated transformer. 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. Trapped five band EFHW SOTA antenna. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. It performed well on both the 2m and 70cm bands. This article will not address that antenna type. I then used a piece of heat shrink on the outside to hold everything in place. 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. 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. There is lot of controversy around the EFHW antennas. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Wow, Gary! With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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. 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%. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. 2. Klubunknl folyamatos a tagfelvtel. The overlaid VSWR plots are shown below. There is much more that can be written about this antenna and its matching, but that was not my aim. The results are presented below. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Frank VK1VK. Above is a thermograph of the transformer at 20W input at 3.6MHz. Not the ideal antenna, but convenient! However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. I installed a QRP SWR meter into the tuner that makes tuning very handy. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none.
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