On 16 July 2015 at 23:23, Bob Camp <[email protected]> wrote: > Hi > > Quick and simple: > > 1) Signal power is proportional to the area of the loop. Bigger is better. > 2) Inductance is proportional to the turns squared. Turns do not directly > affect signal to noise. > 3) Inductance may be resonated with a capacitor. This gives a bandpass > function. > 4) The coil shapes are very common. The many inductance calculators on the > web will give you an inductance estimate. > 5) If the inductance is resonated, the system Q (and thus bandwidth) is a > function of the coil losses and the amplifier’s input impedance. > 6) More turns gives a power match into a higher impedance ( more voltage). > 7) *Practical* matching of the amplifier to the antenna will give you an > reasonable target number of turns. > > Bob >
It's interesting that http://www.vlf.it/feletti2/idealloop.html says that sensitivity is set by the mass of copper used. To quote "A single turn square loop, 1m side, made with 1kg copper has the same sensitivity of a 1000 turns square loop made with 1kg copper and same dimensions. In this context, the sensitivity limit is represented only by loop thermal noise: noise floor (nV/sqrt(Hz)) = 4 sqrt(R in kOhm)" It is not immediately obvious where that equation comes from, but re-arranging the equation for thermal noise power P=k T B (P in watts, k= Boltzmann contant, B is bandwidth in Hz) and assuming a temperature T of 300 Kelvin, k = 1.38 x 10^-23 J/K, one finds the constant is 4.06, so the 4 in that equation is fairly accurate at 300 Kelvin. I'd much rather wind a loop with a few turns than a few hundred turns! But obviously the voltage rises with the number of turns, so requires less gain. Dave _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
