1 files changed, 8 insertions, 2 deletions

diff --git a/3.-Direction-Finding-Background-Theory.md b/3.-Direction-Finding-Background-Theory.md
index 6dd7bac..6edc5f9 100644
--- a/3.-Direction-Finding-Background-Theory.md
+++ b/3.-Direction-Finding-Background-Theory.md
@@ -10,7 +10,11 @@ However, radio direction finding bearings will always have inaccuracies of sever
 
 **Directional Antenna Based:** These methods use a directional antenna like a Yagi and have a user sweep the antenna around searching for the direction of the highest power. This direction is then recorded. These steps are then recorded at other locations until triangulation is achieved.
 
-**Pseudo-Doppler:** Pseudo Doppler methods make use of a fixed antenna array where each element is rapidly activated for a brief period of time in a rotating fashion. This simulates a single antenna actually rotating on a horizontal wheel rapidly. With this doppler data about a signal can be extracted, hence finding a bearing towards it. This is the method used by LoJack, Opera Cake.
+More automated methods may make use of an array of directional antennas in a circle.
+
+**Pseudo-Doppler:** Pseudo Doppler methods make use of a fixed antenna array where each element is rapidly activated for a brief period of time in a rotating fashion. This simulates a single antenna actually rotating on a horizontal wheel rapidly. When the rotation is moving towards the signal, the received frequency should increase. When the rotation is moving away, the frequency will decrease. With this information we can determine a bearing towards a signal. Pseudo-doppler is the (older) method used by LoJack, which allowed Police to track stolen vehicles.
+
+There are several amateur radio pseudo-doppler devices that use a standard scanner radio, for example the RDF42 and the DDF2020T. An open source implementation of Pseudo-Doppler is Opera Cake for the HackRF. 
 
 **TDoA:** Time Difference of Arrival (TDoA) methods require multiple time synchronized radio units to be separated over some distance. Differences in the time a signal is received are collected by each unit, and this information can be used to calculate hyperbolic curves between receivers. This is the method KiwiSDR uses.
 
@@ -27,5 +31,7 @@ So, if we take a singular reading at a location where the multipath effect is st
 ## Mobile Vehicular Operation Theory
 
 Many simple radio direction finding systems will have the user drive to different locations, take a manual reading and plot that bearing on a map. 
-With the KrakenSDR system we make use of modern smart phone technologies such as mapping, GPS and compass sensors. We take hundreds of readings by automatically logging bearings generated by the KrakenSDR against the current location and heading determined by the smartphone sensors as the vehicle moves. The system over time generates an average intersection of these bearings, pinpointing the location of the transmitter. We make use of the smartphone mapping service MapBox to plot this data on a map for easy human visualization.
+
+With the KrakenSDR system we make use of modern smart phone technologies such as mapping, GPS and compass sensors. We take hundreds of readings by automatically logging bearings generated by the KrakenSDR against the current location and heading determined by the smartphone sensors as the vehicle moves. The system over time generates an average intersection of these bearings, pinpointing the location of the transmitter. We make use of the smartphone mapping service MapBox to plot this data on a map for easy human visualization, and even have a turn-by-turn navigation feature to help take you directly to the transmitter without needing to consult a map.
+
 Advanced Feature: The KrakenSDR app actually does something cleverer than calculating simple intersections of bearing lines. It uses the full 360 degrees of data given by the correlative interferometry algorithm. This 360 degrees of data includes multipath direction data too. It then overlays this data on a grid, activating each cell that the 360 degrees of data lies on by some scaled amount. Over time, the cell with the most activations is deemed to be the one containing the transmitter location.