efhw compensation coil

I will go back and have the article corrected. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. But I would caution its usage for higher power than 10-15W. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The toroid with its many taps may be soldered directly on a multi-position switch. This will yield the maximum capacity of the variable capacitor. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. 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 band compensating inductor placed on the wire is another story. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different 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. Simulating the end-fed half-wave (EFHW) 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" Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite Be aware counterpoise or ground radials are required for all hf antennas for better performance. 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. Consequently, this is how the capacitance values are determined. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. This will also be handling 100W. Jim, do you mind if I add your email and my answer as a comment to the article? 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. Some hams swear by them, yet some completely demean it. 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.

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