Mighty Mouse 2 compared to Mighty Mouse 1

Tri-M sent me two of their Mighty Mouse 2 (in short: MM2) low cost GPS antennas. I added the factory specification to my antenna table, you can compare the specs with some other popular antennas.

According to the factory spec the MM2 is 'different' in the following areas:

  1. It operates down to 2.0 VDC
  2. It consumes only 5 mA
  3. It has an integral 2MHz bandpass filter to mitigate interference effects.

Because 'seeing is believing', I did some tests to verify the factory specs. The results of my tests are given below.

1. Supply current test

I connected the antenna's to a variable power supply and measured supply current as function of supply voltage:

5.0-2.5 VDC 2.0 VDC 1.7 VDC
Antenna1 5.5 mA 4.0 mA 3.0 mA
Antenna 2 5.3 mA 3.9 mA 2.9 mA

Supply current is slightly higher than spec'ed (5 mA), but drops to an all time low of  about 3 mA at 1.7 VDC. And the surprise is that the antenna's still operate reasonably well at this low voltage (see 2 below).

2. Supply voltage test

The antenna's were succesively connected to my u-blox PS-1 receiver. Power was supplied by the variable power supply, connected via a splitter between antenna and receiver. I noted carrier-to-noise (cno) ratio of all sats (8) tracked by the receiver. At supply voltages between 5.0 and 2.5 VDC the values remained CONSTANT. The table below shows the decrease in cno at lower supply voltages, compared to the constant value.

2.0 VDC 1.7 VDC
Antenna 1 -2 dB -4 dB
Antenna 2 -2 dB -4 dB

It was a pleasant surprise to see that both antenna's worked OK at 2 VDC, with only a slight decrease in cno. Tracking of low elevation satellites may be lost. Even at 1.7 VDC the antenna's still functioned, be it with a significant decrease in cno, and my receiver lost track on two low elevation satellites (7 deg and 13 deg), but kept track of sats with an elevation of 16 deg or higher.

3. Sensitivity of MM2 compared to MM

With the antenna on top of my roof with an unobstructed view I recorded about 2 hours 45 minutes of data, first with the MM2 connected to the receivers, and two days later (to be exact: 1 day 23 hours 52 minutes and 8 seconds to obtain an identical constellation) with the MM. This experiment allows a realistic comparison of the sensitivity of the MM2 and the original MM. The 4 graphs below show the cno value reported by the receiver as a function of time for prn 01, 16, 18 and 19. Graph 5 shows azimuth as a function of time, and graph 6 elevation.

 

The graphs show no clear winner. Sensitivity of MM2 is roughly equal to MM. Cno values are in the order of 47.5dB for all sat's with an elevation above 40 deg. Below 40 deg cno values reduce to about 40 dB at 10 deg elevation (prn 19).

But note the behavior of prn 01 and 16 around 410000 sec and prn 18 around 416000 sec. The 'spikey' behavior of the cno for both antenna's is a result of MULTIPATH reception. And note that the elevations are over 75 deg! So, even with a clear view to the sky, multipath reception DOES occur, and in my case for sat's with a high elevation! And check the striking correlation of cno and multipath in the graph below (multipath up to 10 m with cno varations of 3.5 dB).

4. Azimuth sensitivity

Under construction

5. Interference mitigation

I tried to check the effectiveness of the passbandfilter of the MM2 by approaching a local TV station with my u-Blox receivers, one with the MM connected and the other with the MM2. The station has its third harmonic right in the L1 band (10MHz around 1575.42 MHz). No difference found! An example of a failed test!

Recently I happened to be close to the 'Flycatcher', a short range air defense radar operating in the I-band (8 - 10 GHz), and I noticed that my Garmin 12XL lost lock if close to the radar. Apparently the radar spills some energy in the GPS L1 band.
I also got with me an MM2 and a Lowe active. With the Lowe active connected to the 12XL I walked slowly towards the radar. The receiver lost lock when I was appr. 120 m away from the radar. I repeated the experiment with the MM2 connected, and the receiver stayed in lock until 40 m away from the radar, a three-fold improvement over the Lowe active!

Of course this test is too limited to make firm statements about the interference suppression of the MM2. I wellcome suggestions for additional relevant tests.

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