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Diffstat (limited to '4.-Antenna-Array-Setup.md')
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diff --git a/4.-Antenna-Array-Setup.md b/4.-Antenna-Array-Setup.md index 5b0e05d..b156d01 100644 --- a/4.-Antenna-Array-Setup.md +++ b/4.-Antenna-Array-Setup.md @@ -72,16 +72,17 @@ The other way to set up an array is to use a uniform linear array (ULA), which i The advantage of ULA is greater accuracy resolution due to a larger possible aperture. But this greater accuracy only applies to signals that arrive at angles near to orthogonal to the array. The effective aperture will appear to be much smaller near the 0- and 180-degree edges of the array. +Think of how much array surface area a signal 'sees' from the edge of the array, compared to when orthogonal to the array. Therefore, linear arrays are only recommended for certain situations where you know the general direction of a signal, and know that it will not stray too far to the sides. + The interelement spacing calculation is the same formula as for UCA. `I_e = sλ` # Antenna and Coax Precision -The KrakenSDR will not compensate for phase distortion in the external antenna system. -Therefore, you must use identical antennas, and lay out your antenna array as precisely as possible, so we recommend using our templates. A tip is to measure the interelement spacing between elements after placement and confirm that all measurements are identical. +The KrakenSDR will not compensate for phase distortion in the external antenna system. Therefore, you must use identical antennas, identical coax cables, and lay out your antenna array as precisely as possible. We recommend using our array spacing templates to help with this. One tip is to measure the interelement spacing between elements after placement and confirm that all measurements are identical. -All the coax cables connecting the antennas to KrakenSDR must be identical lengths to a tolerance within a centimeter or less. If cables have different lengths, then direction finding will not be possible. +Up until about 900 MHz, all the coax cables connecting the antennas to KrakenSDR must be identical lengths to a tolerance within a centimeter. If cables have different lengths, then direction finding will not be possible. The higher your frequency of interest, the more precise you need to be with your antenna position layout and coax length tolerances. For example, at 800 MHz a 1 cm difference between coax cable lengths in the array could result in a phase distortion between elements of up to 14 degrees. At 400 MHz the same 1 cm difference results in 7 degrees distortion. |