It is worth experimenting with its length also. Lets do a quick calculation to see how much an issue is this output capacitance. Some website features may not function optimally without cookies. This will also be handling 100W. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. I also will ask, why didnt it work for you. We use cookies to optimize our website and our service. 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. By using traps, the antenna works on all three bands with no operator interaction. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Very interesting design. I decided to play with this to see what I could accomplish. I can give a link if you need. What are its disadvantages? For . Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. 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. I ran WSPR at 10mW for about 2 hours and got the results below. A Smith chart view of EFHW transformer compensation Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. The final turns ratio turned out to be 3:29. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube 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. How badly can high Local Ambient QRM affect HF Radio? Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. I decided to push for best efficiency with a 5-turn primary. Above is a sweep of the uncompensated prototype with a 3220+50 load. Pocket-tenna core is finally done! Wire and compensation coil being Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. What kind of balun is this? Change). 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. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. Understanding Antennas The Good, the Bad, and the Ugly. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. A short 80m antenna for my lot - KB6NU's Ham Radio Blog For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. Isn't it? MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Low SSN Why do most Hams find HF Radio so difficult? End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 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. 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. Thirty turns #28 are wound on the two FT114-43 cores. Can I get away with no capacitor in my design? The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. It may be one or even five kilo-ohms. The parasitic reactances near the feed-point also vary between installations. My End-Fed Half-Wave (EFHW) AmateurRadio.com Wrap the first wire around the toroid 27 times (I used a black wire for this). It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. = .000001 / 3868.88 This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. With no counterpoise wire it will be the coaxs shield providing it. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. This will yield the minimal capacitance of the variable capacitor. One end is about 5 meters high on an extended fishing pole. 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. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. stream Zin=46.52+j6.72. 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. (LogOut/ Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Trapped five band EFHW SOTA antenna. P.S. One possible explanation is that the core losses drop with temperature. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Frank VK1VK. 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! You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Csatlakozz csapatunkhoz! From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. I will go back and have the article corrected. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. I decided to play with this to see what I could accomplish. 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). It is quite possible that designing more than three or four bands into a tuner will lead to a failure. = .00 00 00 00 0 258 Looking at several builds and discussions, such as commercial antennas (e.g. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. Wow, Gary! This provides proper insulation from the relatively high voltages on the seconder winding. 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). Thank you for an interesting and informative read. 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. The End-Fed Half Wave Antenna a bit Differently This is perhaps one of the most hotly debated rookie topics in. EFHW Antenna Frequency Compensation Lead - YouTube EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. 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.
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