Review of Silva Multi-Navigator / Brunton MNS GPS device
This GPS device is manufactured in UK and is sold under both Silva and Brunton brands. It was one of the first GPS devices to incorporate an electronic compass and barometric altimeter. It has similar features to the Garmin eTrex Summit. Both of these seem to be aimed at the outdoors market, and they both lack the ability to import maps. My comments below are based on version 2.13 of the Silva / Brunton GPS firmware.
The Silva / Brunton device is large (170 mm x 61 mm x 30 mm) and relatively heavy. Silva quote a weight of 254 g including batteries, but my measurement is 270 g including 2 alkaline batteries. It comes with a durable case that weighs a further 50 g. (Garmin claim dimensions of 112 mm x 51 mm x 31 mm, and a weight of 160 g including batteries, for the eTrex Summit. The Garmin GPS is thus considerably smaller and lighter.)
An article in issue 18/2000 of Finnish magazine Tekniikan Maailma is said to indicate that, with GPS function switched on, current consumption of the Silva device is 210 mA (or 270 mA with illumination on), which seems to be a relatively high figure for a GPS. This appears consistent with Silva's modest claim that, with continuous use of GPS function, batteries will last up to 10 hours. The device takes 2 AA batteries. There is no provision for an external antenna.
Waypoints, routes and tracks
It has capacity for a generous 1,000 waypoints and 5,000 trackpoints. However, only 10 routes can be stored, albeit with up to 100 waypoints each. I find 10 routes restrictive, and would have preferred more routes with fewer waypoints.
Waypoints may have names up to 8 characters long, and there is a dedicated altitude field for each waypoint. If storing the current GPS fix, the elevation recorded is that measured by the barometric altimeter. A feature previously missing—an averaging capability when determining the current GPS fix—is apparently available with version 2.16 of the firmware. However, the device is let down by the lack of provision for icons and a waypoint comment field. Furthermore, estimated position error is not shown.
The tracklog stores GPS easting and northing co-ordinates for each trackpoint. It also stores elevation data, the elevation apparently taken from the barometric altimeter rather than the GPS fix. But the tracklog is of no use in the field, as there is no access to it without download of data to an external device. The tracklog cannot be saved as a route, it cannot be used for backtrack navigation, and trackpoints cannot be viewed.
Tracking of satellites
The Silva / Brunton device does not use, and apparently does not receive, the correction signals transmitted by WAAS / EGNOS satellites. This means that the position and elevation data provided are likely to be less accurate than the output from a device with such capability.
The information supplied for the Silva / Brunton GPS indicates that the device "performs in harsh conditions such as bad weather, inside vehicles and under canopies of trees". I have done a basic test of this device in difficult reception conditions, making a comparison with a Magellan SporTrak Map—a few details are indicated in the footnote. What I found was that the Silva / Brunton performed adequately in difficult reception conditions, but the Magellan was undoubtedly better at coping with weak signals. So the performance of the Silva unit in such conditions appears adequate but not exceptional.
The electronic compass works well and can be used, with GPS function switched off, to point the user in the direction from the last GPS fix to any preselected waypoint. The instrument must be held level for the compass to work reliably, and there is a bubble-level to assist the user. There is direct access to the compass when the GPS is switched off, by pressing a compass button on the keypad. The backlight comes on automatically when the compass is used in this manner. The compass is claimed to be very economical on batteries, and the instructions suggest using the compass function on its own, whilst occasionally switching on the GPS to allow the bearing to the destination to be automatically updated. In this way the GPS can be used as a magnetic compass, but without the inconvenience of having to transfer a bearing from GPS to a separate compass. This could be of benefit in very cold conditions where manually setting a compass could be tiresome.
The barometric altimeter maintains a log of barometric pressure, but not altitude, even when the device is switched off. It is claimed that this background function is very economical on batteries, and my experience supports this claim. Barometric information at hourly intervals is available for the previous 36 hours, but only one hour at a time can be viewed on the screen. The barometric log provides input data for an automatic weather forecasting function. This function seems to work as a rough guide.
Elevation readings appear accurate, allowing for the need for calibration. If the tracklog is switched on, then elevation is logged as part of the tracklog. But, as commented earlier, the tracklog data (including elevation information) are inaccessible until downloaded.
Maximum and minimum elevations are registered even if the tracklog is switched off. Rate of elevation change is displayed if the device is switched on, but the use of rounded feet per second is of limited use for hiking. The indicated rate of elevation change can seem disconcertingly volatile, probably because measurements are made over a very short interval and are affected by pressure transients. The following are all unavailable: total ascent, total descent, average ascent / descent rate, maximum ascent / descent rate, and elevation profile.
The barometric altimeter is calibrated manually when at a known elevation. There is no possibility of automatic calibration from GPS function, although the elevation from the GPS function is accessible if required.
Keypad and screen
The keypad is exemplary—big backlit keys with a good action. The device is thus easy to use in dark or cold conditions.
It is claimed that the device is usable down to -25°C, a considerably lower temperature than for many comparable devices. I have tested the device at -20°C, and can confirm that the screen works well at that temperature, although it is slightly slow to respond.
Otherwise, I do not like the screen. Amongst other things the decimal point is very small, making it hard to read certain measurements, eg distances. Numeric character 5 is spidery and is a slightly odd shape to my eye. And the plastic window on the case causes reflections that frequently impair visibility of the screen.
The LCD screen does not seem to be a true graphic display, which may explain the device's inability to provide scrolling menus and a map image of waypoints etc (see below).
As indicated above, the screen works at low temperatures. The Silva sales leaflet asks if there is any point in trying to use a GPS during a mountain search and rescue mission if it does not work in low temperatures, especially taking wind-chill into account. [By way of digression, one might comment that wind-chill is only relevant to inanimate objects in that it will increase the speed with which such objects reach the ambient temperature.]
My experience at an ambient temperature of -32°C did reveal one possible problem. When I booted up the device the internal thermometer gave a reading of -13°C, which was doubtless correct as the device had been in a rucksack and thus partially insulated from the cold. At that temperature, and using relatively new Energizer lithium batteries, I attempted to use the "Goto nearest waypoints" function with the screen backlight switched on. The function did not work and I received a low battery warning. The device was however able to obtain a GPS fix. There are signs here that the current drain may potentially exceed the capabilities of high performance batteries at low temperatures.
There is also a practical issue relating to size. At low temperatures, it may make sense to keep a GPS device warm, eg by keeping it in a trouser pocket. Unfortunately the size of the Silva device makes this relatively impracticable. It therefore appears that a compact GPS device with nominally inferior low temperature performance may work better in practice as it is much easier to keep it warm.
The screw on the battery compartment is small, and I find it awkward to change batteries in the field. It is not possible to remove the cover with a quarter turn—the screw must be completely unscrewed from the GPS. On my GPS the screw tends to drop out of the battery cover during battery change, so it could be lost.
The lack of a proper menu system seems to me to be a significant weakness. There is no scrolling capability—for example, it is not possible to move a highlight bar up and down a list of options (eg waypoints and routes) for selection purposes. And command options are not concurrently presented in the form of a menu. The device therefore does not seem user-friendly, and the user needs to work through a hierarchy of functions that cannot be read off a menu. By the standards generally prevailing, the user interface seems very rudimentary.
There are also inconsistencies. When the GPS is in "view waypoint" mode there is a selection short-cut, by pressing the YES button, which takes one to a "find waypoint" routine. But if one tries pressing the same button when in "delete waypoint" mode that does not happen—instead, the current waypoint is immediately deleted without any request for confirmation. This seems to me to be poor design.
Transfer of data
I have investigated certain software options for transfer of data between GPS and PC. I have experienced consistent corruption of data in certain conditions using Silva's own Global Map Planner software, and I suggest that this software should be avoided. Topografix have developed their various software options for use with the Silva / Brunton GPS, and they seem to work so long as limited map datums are acceptable. Oziexplorer works well with the Silva / Brunton device—it supports a wide range of map datums, and may appeal to more ambitious users. Fugawi also claim to support the Silva / Brunton device, but I have not carried out proper tests on this software.
European users may note that until late summer 2002 Silva, unlike Brunton, seemed to have a policy that the proprietary data cable could only be bought with the Global Map Planner software. It now appears that Silva has reversed this policy. Belatedly, it is therefore possible for European users to buy the cable without purchasing Global Map Planner.
The GPS is not a mapping device—in other words it cannot import maps.
Surprisingly, unlike the great majority of GPS units, it does not offer an internal map image of waypoints, routes or tracks. That may explain why Silva did not bother to provide icon support for waypoints. Map images of waypoints etc are normally provided in handheld GPS devices, and the lack of this capability seems to be another significant weakness.
My experience of Silva customer support has been poor. I imagine that Brunton may well be better.
The Silva / Brunton GPS has an electronic compass and barometric altimeter that work well. But, viewed as a GPS, I do not believe that it is a competitive product. Given that it seems to be aimed at the outdoors market, the size and weight of the device seem to be a significant disadvantage. And it has other weaknesses, eg lack of a proper menu system, absence of map screen, lack of waypoint icons and comments, relatively high battery consumption in GPS mode, unavailability of tracklog and backtrack in the absence of a separate computer, and difficult battery change. Furthermore, it does not support WAAS / EGNOS. Anyone who has used a recent consumer GPS device from one of the main manufacturers would be liable to find that the Silva / Brunton GPS is curiously lacking.
The Silva / Brunton GPS is not cheap. In the North American market it appears that it is possible, for the same money, to purchase a much more highly specified GPS with barometer and 3-axis electronic compass.
The Silva / Brunton GPS does have strengths. It has an excellent keypad, and an LCD screen that operates well at low temperatures. It also has a rudimentary barometer-based weather forecasting capability. If these features, or an electronic compass, are more important than general GPS functions, then the Silva / Brunton device may be worth considering.
09 November 2003
Footnote—performance in difficult reception conditions
I have done a brief comparative test of the Silva / Brunton GPS and Magellan SporTrak Map in difficult GPS reception conditions.
I kept a tracklog on both instruments (Silva with one minute track readings, supplemented with manual track points at corners, and the Magellan with auto-detailed track setting). As the Silva GPS has a patch antenna and the Magellan a helical antenna, I held the Silva unit horizontally and the Magellan unit vertically.
Carrying both instruments, I covered a distance of 850 metres with an elevation gain of 150 metres—I went along a path which slants up the north-facing slope of a steep hillside, where there is moderate tree-cover and where a substantial part of the southern sky is obscured by the hillside. I then returned on exactly the same route to see how consistent the tracks were for the outward and inward legs.
Both units coped reasonably, but the Silva unit performed less well. To the extent that the Silva instrument provides information about signal strength, it seemed that it was getting a weaker signal. The Silva unit sometimes picked up fewer satellites than the Magellan GPS, and it had a greater tendency to drop to 2D mode. At one point the path took one for a few seconds under a masonry bridge. At that point both units lost all satellite signals. The Magellan unit recovered almost instantly, but the Silva unit took a few seconds to recover.
On downloading the tracks to Oziexplorer, it could be seen that the Silva unit was less consistent for the whole exercise. The Silva's tracks on the outward and inward legs consistently showed greater divergence, with a maximum discrepancy of about 67 metres. (The greatest discrepancy for the Magellan was about 45% of that figure).