I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. coil inductance calculator at 66pacific.com. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. So, I embarked on testing it for myself. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Jos van den Helm's (PA1ZP) article published in Radcom: 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. The antenna is effective and the materials and construction are of a very high quality. 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. . 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 . It is important to consider the voltages on this tank circuit. Current Balun 1. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. The final turns ratio turned out to be 3:29. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. I am currently working on measurements of an EFHW antenna. So, how to construct an end-fed half wave antenna? Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. I used the 14g enameled wire and wound it on the FT240-43. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Can a diode be used to rectify signals smaller than its threshold voltage? End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer How far could it possibly reach? 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. Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. ON7EQ EFHW Antenna - qsl.net The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Software Engineer - EDI - salary.com The computation method is also touched on. 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. |k"^N>F.AnJkJsq'PV}o0I. The photos above show a method that works fairly well. How to get started on ISS Cross band Repeater? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. %PDF-1.4 I needed to add an additional coil (approx 12.5 uH) about . 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. We use cookies to optimize our website and our service. Thanks! Simulating the end-fed half-wave (EFHW) dipole antenna To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 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. Next, I started winding the transformer. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. Thank you Gary. The original coil is designed for low power portable applications. EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com Zin=46.52+j6.72. These dimensions were derived from modelling the antenna in EZNEC. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. 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. We do not know what the actual impedance will be at the end of the antenna radiator. With no counterpoise wire it will be the coaxs shield providing it. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Trapped five band EFHW SOTA antenna. A short 80m antenna for my lot - KB6NU's Ham Radio Blog I ran WSPR at 10mW for about 2 hours and got the results below. 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. The previous table already contains these measurements. (LogOut/ You cant really see the antenna wire, but the red line shows the antenna path. Start by wrapping the wire around the toroid. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Consequently, this is how the capacitance values are determined. The 40-10m EFHW camping antenna is late but done. More info in - reddit I first mounted the SO239 connector to the box. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. EFHW Compensation Coil Experiment - YouTube The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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.) http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. However, a key restriction is its 25W power rating, due to the small matching transformer. Krem, rja le, mi a krdse. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). This graphical depiction makes it easier to visualize the current and impedance correlation between bands. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. For a quarter wave that is about 8 nS. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Nagyon j ez a cikk. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. See the table above. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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 are the advantages and disadvantages of the end-fed half wave antenna? 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. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. Graphed with a log scale, it makes a nice straight line. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. 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. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" Many people use an inductor placed at the near end to make things level out on the higher bands. Thank you for an interesting and informative read. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? = .000001 / 3868.88 Regards VE9HAM. My design objectives were: 1. Do I count the six loops around the pvc in the measurement? It depends on the selection of the inductance and the capacitor values. From that we can find Mismatch Loss. Also find news related to Efhw Compensation Coil Experiment which is trending today. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. 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). 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. We also need to know what are the frequencies or bands for which we plant to use this antenna. I am planning to use this latest one at the Field Day next year. Best regards and thanks again for your comment. Jim, do you mind if I add your email and my answer as a comment to the article? I wish you lots of productive experimentations and successful portable operations.

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