The Micro Mouse
Tri-M introduced the Micro Mouse GPS antenna at the end of 2000. It's a member of the 'Mighty Mouse' family of antennas, but substantially smaller. The key data are given in the antenna table, the figure below shows the Micro Mouse together with the Lowe Active antenna and the Mighty Mouse II.
The electrical specifications differ not much from the Mighty Mouse, so I decided to compare the Micro Mouse with the Mighty Mouse in the following experiment.
The antenna was placed on the rooftop of my house with a free view over the
sky above the horizon. The antenna was connected to my BAE Systems 'Superstar'
GPS receiver. The raw data output of the receiver (for each sat in view once
per second pseudorange, carrier phase, signal strength) was logged on a PC.
On four consecutive days (19 to 22 December 2000) I recorded from about 7 PM to 11 PM with the following antenna configurations:
19 Dec: Mighty Mouse, no ground plane
20 Dec: Mighty Mouse on a circular (40 cm dia) groundplane
21 Dec: Micro Mouse on the ground plane
22 Dec: Micro Mouse, no ground plane.
I compared signal strength (CNO) for each satellite by shifting the time of day by 4 minutes per day (the satellite constellation repeats itself after 23 hours 56 minutes). and came to the conclusion, that the performance of the Micro Mouse differs very little from the Mighty Mouse, both for the configuration without ground plane, and with ground plane. The figures below for PRN 03 are typical for all sats in view. The first figure compares the data of 20 Dec (Mighty Mouse on ground plane, purple trace) with the data of 21 December (Micro Mouse on ground plane, green trace).
The second figure compare 19 Dec (Mighty Mouse, no ground plane, black trace) with 22 Dec (Micro Mouse, no ground plane, blue trace).
It is very obvious from the figures, that the effect of the ground plane is dramatically. To amplify this statement I also plotted the Micro Mouse with ground plane (21 Dec, green trace) together with the Micro Mouse without ground plane (22 Dec, blue trace), see the figure below.
The large variations between 67000 and 69000 sec time of day are due to multipath reception. The ground plane reduces multipath reception quite heavily, and keeps the signal strength almost constant during the interval from 67000 to 79000 seconds of day (the elevation of PRN 03 in this interval started at 20 deg, went up to 87 deg at 73400 sec and went down to 45 deg).
Again I emphasize that the above described behavior of PRN 03 is typical for all sats recorded in the interval. And again I stress the importance of any ground plane, even if your application forbids the use of a ground plane with appreciable size.
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