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From: Stefano Ik5IIR
Date: 13 Apr 2003
Time: 18:57:02
Remote Name: 213.45.101.138
Hi Alan, I report here your interesting post about some indirect ways to measure the efficiency of the EH antenna (any antenna) ..you said: Hakon - I agree with your idea and the efficiency is equal to the ratio of the lossless bandwidth to the actual bandwidth because it is the same ratio as the radiation resistance to the total resistance. The lossless bandwidth equals F0/Q which is equal to F0.Rrad/X, and the actual bandwidth equals F0(Rrad+Rloss)/X. So the efficiency, which equals Rrad/(Rrad+Rloss), equals the lossless bandwidth divided by the actual bandwidth. That is a good approximation provided Q is 10 or more, as it often is for small antennas. It is a good way of estimating efficiency when the loss resistance cannot be measured directly . . . 73s Alan OK..so: the EH antenna Rick (Dj0ip)is using has about 400 khz of BW @-3db or about 200 khz of BW at 2:1 SWR.The antenna is 1%wavelenght at 7 mhz. hence the antenna Q is about 17.5, the lossless BW is about 400 khz at 7 mhz. we measured the loss of 1 db on the radiated signal when the antenna is at his 2:1 SWR range limit. anyway please provide me another definition for the actual BW, because using the Rrad and X the data can be questioned as usual. In fact we affirm to have about 35-J2000 at 7 mhz of impedance for the 40 meters EH antenna when working on the EH mode.Being the EH a dipole installed on the air with no any ground needed , is easy to see how low the Rloss can be.You can calculate the efficiency with the Rrad and X for a low Rloss and the efficiency will be very high too. the above data for the BW @-3db and for 2:1 SWR can be easily measured on any antenna.Thanks for the attention Alan. Stefano Ik5IIR