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Re: Mobius Shielded Loop Antenna

Jack Smith All Messages By This Member #9883 开云体育 John and Andrew are both correct. If modeled as a voltage source in series with inductance, you will find the output voltage into a resistive load is independent of frequency above a certain threshold, just as with the parallel current source model. This is because the loop voltage source EMF increases linearly with frequency at 6 dB/octave (induced voltage is proportional to rate of change of the magnetic flux, so when you differentiate the sin(wt) the flux rate of change becomes -w*cos(wt)) and voltage divider formed by the loop's inductive reactance (which doubles per octave) in series with the amplifier input resistance decreases the signal at the amplifier input at the same 6 dB/octave if the frequency is sufficiently high such that the amplifier input impedance is much less than the inductive reactance of the loop.? In other words, the 6 dB/octave rising voltage output is canceled by the -6 dB/octave voltage divider effect and the net voltage input into the loop amplifier is constant with frequency. This series model predicts the same behavior as a parallel current source, so either may be used provided you take care to get the maths correct. The simplistic -6 dB/octave LR voltage divider assumes, as mentioned earlier,? that the loop's inductive reactance is large compared with the input impedance of the amplifier. Jack K8ZOA On 8/20/2013 6:49 AM, Andrew Ikin wrote: toggle quoted message Show quoted text ? John wrote on August 19, ? Your comment that the loop is a current source with a series reactance is interesting. My understanding, is that a small loop can be considered as a voltage source in series with the inductance of the loop, the ohmic losses, and the negligle radiation resistance.? For a given field strength, the voltage output is proportional to frequency.? The equivalent current source has an output which is proportional to field strength only, and has a shunt, not series, inductance. What am I missing? Tnx and 73 John? KC0G ? ? ?Hi John, ? ? What I believe is happening; the H Field induces a current into loop, this current is not?frequency related. However, as the loop has a rising? series impedance with frequency the loops terminal voltage is the product the induce current x the impedance. Hence we see that the Vout is proportional to frequency. ? This issue of the loops series reactance impeding the current is discussed in a GB patent for the Liniplex loop manufactured by Phase Track in the early nineties. I can't find my copy of this patent. A search for patents by Charles Edward Forster my find it. The Liniplex loop used multiple loops in parallel to?reduce the?series reactance from impeding the current to the amplifier. ? Getting back to the real issue here, we have a loop with output z that is frequency dependant, therefore optimum power transfer to the amplifier will only happen when the amplifier input z matches the loop. ? ? Kind regards ? Andrew _

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