From 56534c204145e56bd3edef8b3d6770cfb88c2bdd Mon Sep 17 00:00:00 2001 From: Eric Teunis de Boone Date: Mon, 25 Sep 2023 16:12:26 +0200 Subject: [PATCH] Thesis: Filterchain: WuotD --- .../chapters/grand_characterisation.tex | 127 ++++++++++++++++++ 1 file changed, 127 insertions(+) diff --git a/documents/thesis/chapters/grand_characterisation.tex b/documents/thesis/chapters/grand_characterisation.tex index 3c23c23..2d77497 100644 --- a/documents/thesis/chapters/grand_characterisation.tex +++ b/documents/thesis/chapters/grand_characterisation.tex @@ -1,3 +1,4 @@ +% vim: fdm=marker fmr=<<<,>>> \documentclass[../thesis.tex]{subfiles} \graphicspath{ @@ -10,6 +11,131 @@ \chapter{GRAND characterisation} \label{sec:gnss_accuracy} +% systematic delays important to obtain the best synchronisation +The beacon synchronisation strategy hinges on the ability to measure the beacon signal with sufficient timing accuracy. +In the previous chapters, the overall performance of this strategy has been explored by using simulated waveforms. +\\ +% ADC and filtering setup most important component. +As mentioned in Chapter~\ref{sec:waveform}, the measured waveforms of a true detector will be influenced by characteristics of the antenna, the filter and the \gls{ADC}. +Especially the filter and \gls{ADC} are important components to be characterised to compensate for possible systematic (relative) delays. +This Chapter starts an investigation into these systematic delays within \gls{GRAND}'s \gls{DU} V2.0\cite{GRAND:DU2}. +\\ + +%\section{GRAND DU}% <<< +\begin{figure} + \begin{subfigure}{0.47\textwidth} + \includegraphics[width=\textwidth]{grand/DU_board_encased} + \end{subfigure} + \hfill + \begin{subfigure}{0.47\textwidth} + \includegraphics[width=\textwidth]{grand/DU_board_nocase} + \end{subfigure} + \caption{ + \gls{GRAND}'s \acrlong{DU} V2.0 inside (\textit{left}) and outside (\textit{right}) its protective encasing. + } + \label{fig:grand_du} +\end{figure} + +% ADC +The \gls{DU} (see Figure~\ref{fig:grand_du}), at the base of every single antenna, is the workhorse of \gls{GRAND}.\Todo{rephrase} +Its protective encasing has three inputs to which the different polarisations of the antenna are connected. +Inside, these inputs are connected to their respective filterchains, leaving a fourth filterchain as spare. +Finally, the signals are digitised by a 4-channel \Todo{n-bit} \gls{ADC} sampling at $500\MHz$. +\Todo{filterchain, ADC properties} +\\ +% timestamp = GPS + local oscillator +The waveforms are timestamped using a local oscillator ($\MHz$\Todo{oscillator}) and the 1\gls{PPS} of a Trimble ICM 360 \gls{GNSS} chip\Todo{ref?}. +\Todo{more timing, oscillator} +\\ + +\hrule +Test GRAND setup $\mapsto$ two channel filter delay measurement +\\ +Outlook: +\\ +\quad Local oscillator (multiple sine waveforms within one second), +\\ +\quad GPS-measurement (pulse + sine per DU) + + +% >>> +\section{Filterchain Relative time delays}% <<< +Both the \gls{ADC} and the filterchains introduce systematic delays. +Since each channel corresponds to a polarisation, it is important that relative systematic delays between the channels can be accounted for. +Otherwise, \Todo{rephrase p} +\\ + +Figure~\ref{fig:channel-delay-setup} illustrates a setup to measure the relative time delays of the filterchain and \gls{ADC}. +Two \gls{DU}-channels receive the same signal from a signal generator where one of the channels takes an extra time delay due to extra cable length. +A second measurement is taken after interchanging the cables. +\\ +The difference between the time delay of the first and second measurements gives twice the relative time delay without needing to measure the time delays due to cable lengths. +\\ +%One of the two channels takes an extra (relative) time delay by extending one of the cables. +%It relies on sending the same signal to two \gls{DU} channels with an extra (relative) time delay for one of the channels. +%After measuring the time delay this way, the channels are interchanged so the other channel receives the extra time delay, and a second time delay is measured. +%This way, the time delay due to different cable lengths can be accounted for without needing to measure their lengths. +%Since the difference between the time delay of the first and second measurements gives twice the relative time delay without this additional time delay. +%\\ + + +% signal +We used a \Todo{name} signal generator to emit a single sine wave at frequencies $30 -- 150 \MHz$.\Todo{check} +With the tools explained in Chapter~\ref{sec:waveform}, the phase of the sine wave in each channel is measured using a \gls{DTFT}\eqref{eq:dtft}. +The phase difference then gives a time delay between the channels. +\\ + +% trigger? + +% cable time delays +In Figure~\ref{fig:split-cable-timings}, the difference between the measurements is approximately $10\ns$. +With cables length of $3.17\metre$ and $2.01\metre$, this is in accordance with the estimated extra time delay of roughly $4\ns$. + +\begin{figure}% <<<< + \begin{subfigure}{0.47\textwidth} + \includegraphics[width=\textwidth]{grand/setup/channel-delay-setup.pdf} + \end{subfigure} + \begin{subfigure}{0.47\textwidth} + \includegraphics[width=\textwidth]{grand/channel-delay-setup-picture} + \end{subfigure} + \caption{ + Relative time delay experiment by sending the same signal to two channels of the \gls{DU}. + The loop in the upper cable incurs a large relative time delay. + A second measurement then interchanges the \gls{DU} channels, moving this time delay to the other channel. + } + \label{fig:channel-delay-setup} +\end{figure}% >>>> + +\begin{figure} + \includegraphics[width=\textwidth]{grand/split-cable/split-cable-delay-ch1ch2-50mhz-200mVpp.pdf} + \caption{} + \label{fig:split-cable-timings} +\end{figure} + +\begin{figure} + \includegraphics[width=\textwidth]{grand/split-cable/split-cable-delays-ch1ch4.pdf} + \caption{ + \protect \Todo{only sine} + } + \label{fig:split-cable-delays} +\end{figure} + +% >>> +\section{Outlook}% <<< + +\begin{figure} + \includgraphics[width=\textwidth]{grand/setup/grand-gps-setup.pdf} + \caption{} + \label{fig:gps-delay-setup} +\end{figure} + + + + + +% >>> +\chapter{Old GRAND} % <<< + Trimble ICM 360 Wanted to use WR, but did not work out. @@ -34,4 +160,5 @@ $\sigma_t \sim 20 \ns$ \subsection{Local Oscillator} Should be $f_\mathrm{osc} = 500 \MHz$ +% >>> \end{document}