efhw compensation coil
High self-resonant frequency. 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 thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. One possible explanation is that the core losses drop with temperature. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. My design objectives were: 1. This gave me an effective coil diameter of 40.5mm. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. P.S. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. 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. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. 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 will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Lowest measured inductivity = 2.0 H. 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. So, how to construct an end-fed half wave antenna? Show more. That is an end-fed, but very different then the half wave construction. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. Zin=46.52+j6.72. Just the bare 80m wire is shown in red. 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 technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. I added some Christmas colored zip ties to hold everything in place. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. The basic question before us is how does an antenna work? It will present its parameters, so anybody with basic home-brew skills will be able to build it. 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. Transmitting on 15 meters was impossible because of RF into the radio. In his article, I will try to bust some of the myths associated with Inverted. It depends on the selection of the inductance and the capacitor values. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. I look at the end-fed as just an extreme example of an off-center-fed antenna. Impressive article and so well done that I may give it a try. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. The results are presented below. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. I also will ask, why didnt it work for you. 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. What kind of balun is this? Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. So far so good. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. In theory, the examination is supposed to be used to help clarify your medical condition and . Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. The latest news about Efhw Compensation Coil Experiment. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. After some internet research, I settled on making the former from a paint roller. The overlaid VSWR plots are shown below. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. I will publish my findings, but I cannot not promise to complete it until early fall. It is recommended to use at least 2W non-inductive resistors for this purpose. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. nanoVNA-H can firmware be updated if it has a broken USB socket? This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. 100W on a Wire antenna! This reveals we only need to compensate for the reactive component. Klubunknl folyamatos a tagfelvtel. To be safe, better not get much above 120 C. At this point, I'm leaning towards the EFHW, but any of these antennas seem . How badly can high Local Ambient QRM affect HF Radio? This will also be handling 100W. However, a key restriction is its 25W power rating, due to the small matching transformer. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. I was curious why this capacitor was added to the transformer. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. I wish I had a simple answer, but really this is where some experimentation can pay off. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The real power limit will be core heating. 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. Lets call this element the LoadAttenuator. That will be the missing resistor in the resistor bridge of the below circuit. Lowest frequency = 7.000 MHz. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The difference here is that the target bands are low frequency. 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. i liked it a lot, you give good ideas, many thanks. 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. It may be one or even five kilo-ohms. Check your inbox or spam folder to confirm your subscription. Workers' Comp. 5) It is very hard to avoid stray capacitance on the output. 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. You can start with the links below. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The SWR figures were as follows: FT240-43 132ft/100pF capacitor 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. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. 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 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The SWR for the 20 meter EFHW antenna was < 1.2:1 All Rights Reserved. You cant really see the antenna wire, but the red line shows the antenna path. I mounted the transformer on a tree for testing. Next, I started winding the transformer. Could it be something to do with the new vertical aerial I had recently installed? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. The next important parameter is the parallel resonant circuits resonant frequency. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. 2015. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. 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. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! The combination of the transformer with the end-fed dipole results in a positive reactance. 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. More designs can be found by Googling "80m loaded dipole.". The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Is it any good? Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. A week or two later I started to notice an occasional knocking sound inside the house. 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. (LogOut/ Refurbishing aluminium antenna parts affected by weather / corrosion. For the last step, I put together a RF choke to use between the radio and the feedline. Wow, Gary! Compensation. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. 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. I decided to play with this to see what I could accomplish. By using traps, the antenna works on all three bands with no operator interaction. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Change), You are commenting using your Twitter account. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. In an urban area we are much more restricted, especially if we need to be stealth about it. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. What are its disadvantages? There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. . = 1/30.e6 = 33 nS. I would mention first its ease of installation. Be aware counterpoise or ground radials are required for all hf antennas for better performance. The model results show the need for a not entirely insignificant counterpoise. This will yield the maximum capacity of the variable capacitor. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. Research salary, company info, career paths, and top skills for Software Engineer - EDI But systems that work better increase the prospects of contacts. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. . IIRC they call it a "compensator". 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. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. 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). Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Although it is simple to build and is a multiband antenna, it has several attributes that . It not a loading coil. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 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%. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en.