From 92056d706e4395d699efa82c07565df09a9f6510 Mon Sep 17 00:00:00 2001 From: krakenrf <78108016+krakenrf@users.noreply.github.com> Date: Sun, 29 May 2022 22:15:58 +1200 Subject: Updated 3. Direction Finding Background Theory (markdown) --- 3.-Direction-Finding-Background-Theory.md | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/3.-Direction-Finding-Background-Theory.md b/3.-Direction-Finding-Background-Theory.md index 6edc5f9..22a563e 100644 --- a/3.-Direction-Finding-Background-Theory.md +++ b/3.-Direction-Finding-Background-Theory.md @@ -22,12 +22,14 @@ There are several amateur radio pseudo-doppler devices that use a standard scann ## Multipath -Multipath is when the signal to be located may be reflecting off some objects such as terrain, buildings or vehicles, and the radio direction finding system may ‘see’ that reflection as the source. This can either skew the bearing away from the actual source, or simply provide a totally incorrect reading. The worst case is when the receiving antenna array does not have line of sight to the signal source, so only the reflections can be seen. +Multipath is when the signal to be located may be reflecting or refracting through some objects such as terrain, buildings or vehicles, and the radio direction finding system may ‘see’ that reflection as the source. This can either skew the bearing away from the actual source, or simply provide a totally incorrect reading. The worst case is when the receiving antenna array does not have line of sight to the signal source, so only the reflections can be seen. An analogous example, you may be indoors looking at sunlight on the wall. If you couldn’t see the sun directly, and didn’t know any better, you might conclude that the source of light is the wall, a mirror or the window instead of the sun. So, if we take a singular reading at a location where the multipath effect is strong due to a lack of line-of-sight radio path, we may come to the wrong conclusion about the signal source bearing. Therefore, to obtain an accurate location, we need to take multiple readings at multiple locations to average out the incorrect or skewed readings we get from multipath. This can be achieved by either having multiple distributed sites with a KrakenSDR and an antenna array at each site, or by moving a single KrakenSDR around by driving a vehicle and taking many readings. +Using a larger antenna array (while still keeping under the half wavelength interelement spacing limit) also helps reduce the effects of multipath. Small arrays have less resolution, so they will absorb multipath corruption into the main lobe, skewing the result. Larger arrays will provide greater resolution, meaning that the multipath signal will appear as a separate and hopefully weaker lobe that can be ignored. + ## 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. -- cgit v1.2.3