Introduction
Recently I have been looking at propagation prediction. I read a very interesting article about propagation drive testing, so I thought I would check my existing GPS units for suitability. Since I replaced my Win7 laptop with a Win10 laptop several years ago, a key thing changed. The original FTDI drivers for various devices no longer work. Inserting the devices cause the computer to go insane (vaca loca!!) with the mouse symbol darting across the screen and windows opening & closing. Not good. So I came up with several solutions and also purchased a new unit with a magnetic base that receives GNSS (GPS/GLONASS/Galileo/BeiDou/).
GPS Gen1 Equipment
Figure 1 shows my existing GPS equipment (minus the iPhone that is taking the picture). My first receiver, a Garmin GPS38 single channel, had an RS-232 output. I used to connect this to an RS-232/USB converter with an FTDI driver, this no longer works. So I purchased a new RS-232 converter with the Prolific PL-2303 driver. My second GPS receiver was a kit using the Trimble Lassen IQ 12 channel receiver. It has a USB output, but uses the FTDI driver as well. My solution is to run Ubuntu 24.04 on VMware and quickly assign the device to the virtual machine before Windows crashes. The third receiver is the RTL-SDR used for GPS reception.
GPS Position Comparison A
| Device | Latitude | Longitude |
| Garmin GPS38 | 43deg 42.602minN 43.7100degN | 79deg 24.088minW 79.4015degW |
| Trimble LassenIQ | 43deg 42.5350minN 43.70892degN | 79deg 23.9610minW 79.3994degW |
| iPhone | 43deg 42min 36sN 43.7100degN | 79deg 24min 4secW 79.4011W |
| Google Earth | 43.7098degN | 79.4013degW |
| StdDevn | 0.0005154deg 0.031min=57m 1min=1Nmi=1852m | 0.0009639deg 0.058min=77m 1min=1Nmi*cos(lat) |
Three GPS units were tested at my home location on the balcony. The view of the sky is limited by high buildings, but I was able to get some readings. Figure 2 shows the elegant mounting arrangement. Figure 3 shows the Garmin & iPhone readings. Figure 4 lists the results with standard deviation.
GPS/GNSS Position Comparison B
| Device | Latitude | Longitude |
| Garmin GPS38 | 43deg 38.0012minN 43.6334degN | 79deg 24.350minW 79.4058degW |
| Trimble LassenIQ | 43deg 37.9982mnN 43.6333degN | 79deg 24.3497minW 79.4058degW |
| GNSS BU-353 | 43deg 38.0009minN 43.6334degN | 79deg 24.3461minW 79.4058degW |
| Google Earth | 43deg 37′ 59.58″N 43.6332degN | 79deg 24′ 20.59″W 79.4057degW |
| StdDevn | 0.0000957deg 0.0057min=11m 1min=1Nmi=1852m | 0.00005deg 0.003min=4m 1min=1Nmi*cos(lat) |
Figure 5 shows the second location B that was tested. Three units were used including the new GNSS receiver. The Toronto Harbour location allows a full sky view as opposed to location A. Figure 6 gives the results, note that the stndev is much better than A which is understandable. Figure 7 show the GNSS serial test screen. More on that in future posts.
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References
#1. – “RTL-SDR for Satellite GPS on OpenCPN”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-satellite-gps-on-opencpn/
#2. – “RTL-SDR for Satellite GPS”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-satellite-gps/
#3. – “RTL-SDR GPS Decoding Tutorial”
https://www.rtl-sdr.com/rtl-sdr-tutorial-gps-decoding-plotting/
