Your suggested dummy equivalent circuitry for SMA is wrong - the series element leg shall be inductance and shunt leg capacitor. In your design it is reversed.
Your presentation of dummy antenna is a simplistic high pass filter with one section where the cutoff frequency is about the frequency of first parallel resonance of SMA. So, your frequency graphs should show attenuation between 0 and F0 ( resonance frequency ).
In actuality, the dummy antenna shall represent a low pass filter with same cutoff resonance frequency
Hi Raphael,
Actually, the low pass was the first topology I considered, if only for the reason it agrees with , which will then add legitimacy to my work. Unfortunately, the low pass dummy results in a modelled impedance (see the bottom right graph in ) that is totally incongruent with Ehrenfried's loop measurement.
Moreover, the low pass dummy exhibits decreasing sensitivity with frequency, which is the opposite of observed small loop behaviour. Link to modelled gain of low pass dummy with LZ1AQ preamp below:
/g/loopantennas/photo/297909/3835201?p=Name%2C%2C%2C20%2C1%2C0%2C0
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It is not hard to understand why a low pass network will have the opposite gain / sensitivity response from the real loop.
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There is a Guanella balun at the output of the proposed dummy aerial (L2 in fig. 5). Can that address your concerns?
Since you did not respond, I will assume that your concern has been addressed by the above statement.
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Placing the transmission line transformer on the input or output makes no difference to the balance. All it does is act as a common mode choke. However on the input side the differential mode impedance is fixed at 50 ohms. On the output side it varies, and contributes to the impedance curve.
Hi Martin,
I just realized that I haven't answered this question. I agree with the statement. I have added a paragraph before fig. 5 to explain the balun placement trade-off. :-) Moving on, there will be a side-by-side performance comparison in version 2, either by me or someone else!
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Thanks again to all reviewers who have unstintingly given their time.
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73, Chin-leong Lim, 9W2LC
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