The efficiency of small transmitting loops, and other parameters, can be had at the following URL:
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It is quite instructive in playing the various trade-offs against each other.?
The big disadvantage of these loops, once you make them large enough to show reasonable efficiency, is the extremely high-Q which results in extremely narrow bandwidth, high circulating currents, and high voltage at the tuning capacitor location.? But they do work.
On Thu, Sep 29, 2022 at 6:31 PM Raphael Wasserman <wassermanr46@...> wrote:
Martin,
The misconseption with Duffy's concept cleared up when I re-wrote his quation differently as:
SND= 10log S / N ext. - 10 log S/ ( Nint + N ext) instead of his final convertion as? SND = 10 log ( N int / N ext + 1 ).
Both equation are mathematically right but the first equation is a better presentation of his concept to understand the logical meaning of SND, likewise we in our business using SINAD knowing we can compare betwen SNR without distortion vs. SNR with a signal distortion and that will?present SNR degradation as difference between both values expressed in dB.
Now I am breaking my brains to find a solution by creating a matching compensation network between Airspy Loop and mine 50 ohms LNA.? My amplifier uses MMIC Darlington amplifier GALI 39 where his input is not designed to see low source impedance/resistance from an antenna. Probably I will use a simplystic T-match LPF like Levko, LZ1AQ did between loop antenna and his balanced common base amplifier. In my case it will be an unbalanced design but using balun between antenna and LPF.The downside in this method it uses one frequency of interest in the calculations of elements vs. more sofisticated matching circuits that use BPF with more L and C elements based on few frequencies.
