I guess you designed this amplifier with recommended LCR equalization circuit in front of it. It is possible two capacitors in series 120 pF each together with the inductance of your transformer winding creates that parallel resonant
frequency. So your presented impedance plot is not for amplifier input but includes front end of your equalization network like your loop antenna would see it.Perhaps the inductance of your antenna is equal to the inductance of transformer winding. If you can estimate both nothing tragic has happened.
Raphael
toggle quoted message
Show quoted text
On Dec 6, 2022, at 1:12 AM, jinze peng <fei666888@...> wrote:
?On Mon, Dec 5, 2022 at 09:16 PM, Raphael Wasserman wrote:
mpedance matching for a broad band application can be discussed? when Ra + j Xa of? antenna impedance can transformed in R inp + j X inp in such way to achieve a maximum power transfer when?4 R a x R inp / | Z a + Z inp | ^ 2 = 1 - |Gamma|^2 for a specified bandwidth from f min to f max of design interest. Have you ascertained that ? That is the function of matching network between antenna and input of your amplifier.
I'm not a math expert, I think for enthusiasts, we just want to know the performance of the equipment, we can't really test the antenna's pattern in the standard electromagnetic shielding laboratory,
we can only try with simple equipment at hand learn.
For the impedance and matching of the common 1m diameter loop, I mainly obtained it by reading Martin's website. I think it is a very intuitive conclusion.
¡°Assuming a typical loop of 1m diameter with an inductance approximately 2 to 3uH, used over the frequency range of 20KHz to 30MHz.At low frequencies<1MHz? the loop behaves as a current source, and the loop needs to have a low value of DC resistance matched by an amplifier with a low value of input impedance.At mid frequencies, typically >1MHz and <10MHz the loop impedance is in the order of tens of ohms and nearly any amplifier with an input impedance in the range >10 Ohms & <200 Ohms will work to some degree. Many poor designs are judged on the basis of signals received in this frequency range, which can be misleading.At higher frequencies when connected to the amplifier, a 1m diameter circular loop, tends to have a resonance at around 30MHz (or just above it), and so it effectively becomes a high impedance voltage source, which requires an amplifier with a much higher value of input impedance, typically peaking to values of around 500 to >1000 Ohms at 30MHz.¡±
I guess the easiest thing is to make the input impedance of the amplifier conform to this conclusion
