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Basically, the loading coil is operating as a trap. The model results show the need for a not entirely insignificant counterpoise. stream The band compensating inductor placed on the wire is another story. The latest news about Efhw Compensation Coil Experiment. Highest frequency = 14.350 MHz. (LogOut/ 3) Total losses are approximately independent of core volume. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. And now I am planning to build one for 160/80m. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. The real power limit will be core heating. Looking at several builds and discussions, such as commercial antennas (e.g. 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 . I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. I installed a QRP SWR meter into the tuner that makes tuning very handy. 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. I particularly want to know how counterpoise affects the common mode currents on the coax. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. After some internet research, I settled on making the former from a paint roller. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. 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. 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The highest frequency could be14.350MHz. I first mounted the SO239 connector to the box. 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. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. You can start with the links below. Best regards and thanks again for your comment. 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. The bridge than will measure zero voltage across the bridge, and the LED will turn off. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Hence, there is no optimum single-fit solution. One end is about 5 meters high on an extended fishing pole. The final turns ratio turned out to be 3:29. 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 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. 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. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. How does this SWR meter works? It does not need any special components; in fact, most of us may have them in our shack drawers already. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Start by wrapping the wire around the toroid. 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. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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 parasitic reactances near the feed-point also vary between installations. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. Graphed with a log scale, it makes a nice straight line. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Elnzst krnk, de elsikkadt az zenete. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. 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 found it very useful to label the tuner with switch and capacitance positions. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. One possible explanation is that the core losses drop with temperature. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Well, in ham radio, everything works. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. The worse SWR was 1:1.7 at the top end of 20 meters. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 2015. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. Hello, a wonderful approach for the problems.. Of course, you will need to find your tuning positions and apply your own position scale. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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 The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 2006. Im very pleased with that indeed. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. The antenna is up. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Thirty turns #28 are wound on the two FT114-43 cores. It performed well on both the 2m and 70cm bands. 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. 5) It is very hard to avoid stray capacitance on the output. Very interesting design. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The antennas are set up as a sloper as in my SOTA outings. 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. This can then, fed with coaxial cable, in many cases be . They will be adjusted for resonance at or close to the CW portion of the bands. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Wrap the first wire around the toroid 27 times (I used a black wire for this).

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