Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! 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. In theory, the examination is supposed to be used to help clarify your medical condition and . The overall lenght is only 15m. 5) It is very hard to avoid stray capacitance on the output. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. Thanks in advance, good health for you in these times, IIRC they call it a "compensator". My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. 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. (LogOut/ Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Lowest frequency = 7.000 MHz. I particularly want to know how counterpoise affects the common mode currents on the coax. It depends on the selection of the inductance and the capacitor values. Thanks again Jim. stream 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). I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 100W on a Wire antenna! An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. This suggests an inductive reactance. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Be sure to take a look for additional analysis and conclusions. The antenna is up. 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. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. 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 transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Now I just need to build or acquire a decent radio to utilize this new antenna. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. Krem, rja le, mi a krdse. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. They will be adjusted for resonance at or close to the CW portion of the bands. 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. Consequently, this is how the capacitance values are determined. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. One end is about 5 meters high on an extended fishing pole. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). This will also be handling 100W. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Even at 15W the voltage at the ends may reach 100-200V. 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. Make sure the first wire is wrapped evenly around the whole toroid. It may be one or even five kilo-ohms. The overlaid VSWR plots are shown below. See the table above. The antennas are set up as a sloper as in my SOTA outings. However, a key restriction is its 25W power rating, due to the small matching transformer. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. We need to measure the inductances of the toroid with the tapped coil. 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. The SWR results are as follows: You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. The equation should have a 10^6 and not 10^-6 in the nominator. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Thanks! Yes, indeed EFHW antennas are very useful for SOTA or other field operation. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. It is important that resonance may be achieved at each tap of the inductance. I decided to play with this to see what I could accomplish. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Let us touch on some necessary theory to begin with. 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. Show more. The technical storage or access that is used exclusively for statistical purposes. Cmzett: Weince joseph How can we help? Hello, a wonderful approach for the problems.. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. The parasitic reactances near the feed-point also vary between installations. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. I checked the wall brackets and mast, but all the fixings were nice and tight. Be aware counterpoise or ground radials are required for all hf antennas for better performance. What are its disadvantages? Refurbishing aluminium antenna parts affected by weather / corrosion. (LogOut/ I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. I decided to play with this to see what I could accomplish. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. View the job description, responsibilities and qualifications for this position. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? The impedance per unit length of a lumped transmission line is where L and C are values per unit length. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. We do not know what the actual impedance will be at the end of the antenna radiator. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. The final turns ratio turned out to be 3:29. 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. = 258 * 10^-12. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). It is worth experimenting with its length also. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Im very happy with the result. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. Then I covered the coil in kapton tape to hold it together. All Rights Reserved. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 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. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. Some say you do not need a counterpoise, but that is false. 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. Transmitting on 15 meters was impossible because of RF into the radio. Highest frequency = 14.350 MHz. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. You can see the coil in the picture below (red arrow). Do I count the six loops around the pvc in the measurement? Change). CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. It uses a coil as a compensation unit, and no counterpoise. It is worth experimenting with its length also. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. 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. I use shock cord to connect the insulator at the end of the wire to my fence. So far so good. <> Well, in ham radio, everything works. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Trapped five band EFHW SOTA antenna. With no counterpoise wire it will be the coaxs shield providing it. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. What kind of balun is this? (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The results are shown below. These dimensions were derived from modelling the antenna in EZNEC. Can I get away with no capacitor in my design? And now I am planning to build one for 160/80m. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. . 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. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Let's find out! It does not need any special components; in fact, most of us may have them in our shack drawers already. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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. So, how to construct an end-fed half wave antenna? It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Check your inbox or spam folder to confirm your subscription. 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. Just the bare 80m wire is shown in red. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Frank VK1VK. Be cautious, such voltages may cause a quite painful skin scorch. Apply for the Job in Software Engineer - EDI at St. Louis, MO. Some hams swear by them, yet some completely demean it. I am building an EFHW antenna for my new. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. 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. It performed well on both the 2m and 70cm bands. 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 . 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. I wish I had a simple answer, but really this is where some experimentation can pay off. It should be no surprise that 80pF is close to optimal. 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'. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Can you give me an idea for your 100 W version, you built for 80/60/40 m. Ismerje meg a hozzszls adatainak feldolgozst . 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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. 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. coil inductance calculator at 66pacific.com. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. 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. Not the ideal antenna, but convenient! I will publish my findings, but I cannot not promise to complete it until early fall. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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. Copyright 2014-2023. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. And not all hf antenna installation are same, with most requiring bit of tinkering. This antenna is only 15m long using 2 loading coils. There are many good descriptions on the net about this type of antenna. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. This article will not address that antenna type. 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). I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. The technical storage or access that is used exclusively for anonymous statistical purposes. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. Could it be something to do with the new vertical aerial I had recently installed? I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. A 100pF silvered mica was connected in shunt with the transformer . 73! You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. How far could it possibly reach? As is often the case, packaging was determined by what boxes I had laying around. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. Nagyon j ez a cikk. You can start with the links below. The equation in the article is corrected now. It performed well on both the 2m and 70cm bands. 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. The EFHW transformer box from outside. I needed to add an additional coil (approx 12.5 uH) about .
Todos os Direitos Reservados à efhw compensation coil® 2015
