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Posted by: Steve / AA5TB Posted On: 06/23/04 Subject: Re: Magnetic Loop Antenna Experiments (Question) Message Posted: In Reply to: Re: Magnetic Loop Antenna Experiments (Question) posted by ak0b on 06/17/04 The radiation resistance of any small antenna will be very low and thus the efficiency will be low too unless the loss resistance is kept much smaller then the radiation resistance. A typical receive only loop is made from small gauge wire, etc., which makes their efficiency low. For a sensitive receiver this is no issue but for transmit its bad as you have alluded to. However, a small loop antenna can be an efficient transmitting antenna as long as the loss resistance is kept to a minimum. This means using a very large conductor, ensure that all connections are electrically sound (no mechanical only joints), brushless capacitors (ex. butterfly), and only air as a capacitor dielectric. There is no limit to how small an efficient transmitting antenna can be in theory. The loss resistance just needs to remain less then the radiation resistance, which quickly drops to very low values as the antenna gets smaller in terms of wavelength. 73, |
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