One possible explanation is that the core losses drop with temperature. The Counterpoise is a short, typically one twentieth (0.05 *. ) 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. The transformer fits sideways in the box with a few millimeters to spare. Cmzett: Weince joseph How can we help? 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. 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. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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. And not all hf antenna installation are same, with most requiring bit of tinkering. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. I can give a link if you need. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. The biggest uncertainty in these measurements was the actual power level used. More designs can be found by Googling "80m loaded dipole.". 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 conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. i liked it a lot, you give good ideas, many thanks. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Lets do a quick calculation to see how much an issue is this output capacitance. 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. 100W on a Wire antenna! One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. The toroid with its many taps may be soldered directly on a multi-position switch. Can I get away with no capacitor in my design? The previous table already contains these measurements. Above, 3t on the primary delivers Gcore<0.002S. 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. Above is a sweep of the roughly compensated transformer. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. Frank VK1VK. Above 7MHz, there is very little temperature dependence at all. It performed well on both the 2m and 70cm bands. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. Wow, Gary! PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC Small efficient matching transformer for an EFHW - owenduffy.net 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. It is best to make the impedance matching adjustable, using switched transformation ratio. (LogOut/ I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. Above is a thermograph of the transformer at 20W input at 3.6MHz. Some website features may not function optimally without cookies. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. I assume you know the GNARC source for EFHW antennas. It should be no surprise that 80pF is close to optimal. A short 80m antenna for my lot - KB6NU's Ham Radio Blog Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Taking the time derivative of the above equation you get the power dissipation. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. Hence, there is no optimum single-fit solution. 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. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. The original coil is designed for low power portable applications. If you stare at the above frequency sweeps you will discover a few things. What kind of balun is this? 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. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH For the last step, I put together a RF choke to use between the radio and the feedline. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. The EFHW transformer box from outside. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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. See the table above. 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. My End-Fed Half-Wave (EFHW) AmateurRadio.com Jim, do you mind if I add your email and my answer as a comment to the article? Could it be something to do with the new vertical aerial I had recently installed? A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I then added two 220pf capacitors in series between the center conductor and ground. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. 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. It uses a coil as a compensation unit, and no counterpoise. 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. In his article, I will try to bust some of the myths associated with Inverted. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. % y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. 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" EFHW Compensation Coil Experiment - YouTube A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. One end is about 5 meters high on an extended fishing pole. Let me review the salient observations from the previous work. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. A 100pF silvered mica was connected in shunt with the transformer primary. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The highest frequency could be14.350MHz. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? The 2 coils are 35uh and 90uh. 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. . Thanks again Jim. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The Truth, ,and Nothing But The Truth (as I've experienced it) I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. 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. I dont have an amplifier, so only need to be able to handle 100W. Thank you for an interesting and informative read. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. There is lot of controversy around the EFHW antennas. P.S. PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. stream The SWR was measured for each of the three antennas across the CW portion of the bands. 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. Although it is simple to build and is a multiband antenna, it has several attributes that . The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Elnzst krnk, de elsikkadt az zenete. Even at 15W the voltage at the ends may reach 100-200V. VK1OD.net (offline). A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out!