Jtdylktuy

I have this tikzpicture/pgfplot (see below). I have a few questions about it.

1. How do you put the x-labels (10¹, 10² and so on) on top of the x-axis?


2. How do you point the y-axis downwards (the arrow below)?


3. How do you place an x-label at the green vertical (at 1591Hz)?


4. How can you put extra ticks on the y-axis without a label (eg. every unit a tick, only every third unit a label)?


5. With those extra ticks from former question, how do you place gridlines alongside of them?


6. Is it posssible to put a dot or a cross on the intersection red-green?


7. Can I also put an arrow pointing to that intersection point with a text label?


8. When I start the domain at 10 instead of 1, or when I use xmin=10, I get a white region between the y-axis and the plot/grid. How can you avoid this. I would like this plot starting with 10¹ at the y-axis.

Thanks very much in advance!

documentclass{article}

usepackage{pgf,tikz}

usepackage{pgfplots}

begin{document}

usetikzlibrary{circuits.ee.IEC,graphs,patterns,calc,positioning,intersections,quotes,decorations.markings,angles,bending,arrows.meta,shapes}

defdBmax{0}

defdBmin{-12}

defpi{3.14159}

defR{1000}

defC{0.0000001}

defFc{1/(2*pi*R*C)}

pgfplotsset{width=14.5cm,height=6cm}

begin{tikzpicture}[scale=0.8]

  begin{axis}[title=$Laagdoorlaatfilter-verzwakking$,

      axis lines=middle,

      ymin=dBmin,ymax=dBmax,

      ylabel={$A_v(dB)$},

      ylabel style={at={(ticklabel* cs:1)},anchor=east},

      ytick={-21,-18,...,0},

      xmode=log,

      domain=1:100000,

      xlabel={$f(Hz)$},

      xlabel style={at={(ticklabel* cs:1)},anchor=south},

      xtick style={above=1cm},

      xminorticks=true,

      xmajorticks=true,

      xminorgrids,

      xmajorgrids,

      grid=both,

      samples=100]

    addplot[no marks, blue] {20*log10(1/sqrt(1+(2*pi*R*C*x)^2))};

%    addplot+[no marks, green] {20*log10(1/sqrt(1+1/((2*pi*R*C*x)^2)))};

    addplot+[no marks, red] {-3};

    addplot+[no marks,green!50!black] coordinates{(Fc,dBmax) (Fc,dBmin)};

  end{axis}

end{tikzpicture}

end{document}

edit:
like this (solved almost all your questions ... )?

(red lines indicate text borders)

documentclass{article}

usepackage{siunitx}

usepackage{pgfplots}

pgfplotsset{compat=1.16}

usetikzlibrary{arrows.meta}



begin{document}

    begin{tikzpicture}[pin edge={Latex-,black}]

defdBmax{0}

defdBmin{-12}

defpi{3.14159}

defR{1000}

defC{0.0000001}

defFc{1/(2*pi*R*C)}

begin{semilogxaxis}[                             % <---

    width=linewidth,height=6cm,                  % <---

    title=Laagdoorlaatfilter-verzwakking,

    title style = {at={(0.5,1.2)},font=itshape}, % <---

    axis x line=top,                              % <---

    axis y line=left,                             % <---

    ymin=dBmin, ymax=dBmax,

    ylabel={$A_v$ (si{decibel})},               % <--- 

    ylabel style={at={(-0.07,0.5)}},              % <---

    ytick={dBmin,dBmin+3,...,dBmax},           % <===

%   ytick={dBmin,numexprdBmin+3relax,...,dBmax}, % alternatively, 

    xlabel={$f$ (si{hertz})},

    xlabel style={at={(0.5,1.1)}},

%

    extra x tick style={% changes for x extra ticks % <===

        tick label style={font=footnotesize,text=green!50!black}, % <===

        grid style={semithick,green},               % <===

                    },

    extra x ticks={1591},                           % <=== 

    extra x tick labels={1591},                     % <===

%

    grid=both,                                       

    minor y tick num=2,                             % <===

    domain=10:100000,                                  

    samples=100,

    no marks]

    addplot[blue] {20*log10(1/sqrt(1+(2*pi*R*C*x)^2))};

    addplot[red]  {-3};

    node[circle,fill, inner sep=1pt,

          pin=45:$f_c$] at (1591,-3) {};            % <===

  end{semilogxaxis}

end{tikzpicture}

end{document}

note:

• 
  tikz libraries should always be loaded in document preamble


• 
  pgfplots load tikz, so it is not necessary to load it (/again)


• better than scaling diagram is to prescribe its width, for example to be equal to text width