Are all GPS antenna's created equal?

[CarinaPDX]

Some thoughts on multi-GNSS receivers:

Global Navigation Satellite System (GNSS) is the generic term for GPS (US), GLONASS (Russia), BeiDou (China) and Galileo (EU). Of these, GPS and GLONASS have been operational for many years now. BeiDou has had good Asian coverage and is building out the full constellation with only 2 active satellites plus the in-orbit spares to go; it will be fully operational in 2020. Galileo is currently in low power mode (so expect weak signals) and will increase to full power this year with full operation in 2020, after 2 more active satellites and in-orbit spares.

GPS/GLONASS receivers have been around for awhile, and benefit a little by using more satellites (I'm guessing about a couple of feet improvement). uBlox has been shipping its uBlox 8 for several years now, and in most cases it receives both as a default. The v2 ROM is capable of receiving three GNSSes, including BeiDou as the third. The current v3 ROM adds Galileo to the choice for the 3 active GNSSes. FWIW while my uBlox 8 receivers do receive either BeiDou or Galileo, and download the ephemeris, the receiver doesn't use them for the solution (yet). I don't really know why, but at this point there seems to be no benefit but I would expect that to change over the next year or so.

Having the capability means nothing unless the receiver is configured for the purpose. The great majority of 8s are shipped with GPS and GLONASS only enabled - even the ones that support Galileo. The factory that produces the puck or mushroom final product can change the default configuration by burning fusible links, and a few seem to have done so. The default can be overridden with a configuration stored in RAM, if the user can do that, and it will be lost on power down and need to be re-entered after power-up unless there is a backup battery (optional). It is also possible to store configurations in either an EEPROM or flash memory, again an option for the producer. A receiver with v2 ROM and flash memory can upgrade to v3 ROM, but usually this is not the case.

For USB pucks it may not be much of an issue to reset the configuration on every power-up with the attached computer, but it is at least a nuisance. For receivers that are feeding a bus or chartplotter there may not be any realistic way of configuring each cycle. So pay attention when buying and look for flash, or a backup battery, if the default configuration is not the desired one.

To configure a uBlox module Windows users will need the (free) uBlox uCenter software, and a bit of study and patience. For Linux install GPSd and use the included ubxtool utility (best to start with v3.19 of GPSd). Look at the tutorials first and it shouldn't be too hard. Mac users are SOL: no one has ported GPSd to the Mac in years.

My most recent USB puck purchase did have a backup battery. I plugged it in a few minutes ago and my configuration was still there after a month of storage. (This is that device: https://www.aliexpress.com/item/32947709096.html) Others that I have checked recently do not have flash or a backup battery, and require re-configuring each time. My new mushroom receiver (https://www.aliexpress.com/item/32848905490.html) has flash inside so I could turn on Galileo as well as change the baud rate to NMEA 0183 HS 38.4kbaud. This required a serial to USB adapter cable as well.

The bottom line is that capability is not of use if it is not configured, so before buying either find one with the right configuration or work out how you will configure the device and get one with flash or a battery. In any event with 2 GNSS being received there is very little advantage to adding more, at this time. Using three GNSSes at one time doesn't seem to add any accuracy, and how many redundant GNSSes do you need?

The next gen is just starting to show up. It will have dual band and all 4 GNSS simultaneously. It still won't put you in the center of the slip (or lane) 100% of the time.

Greg

[Brian.D]

Nice write up. Unless one has an account with Aliexpress, one cannot see the items you mentioned. Maybe give us the model number and not the link. We can look for the item elsewhere.

[CarinaPDX]

Thanks for the heads-up - I had no idea that you couldn't see them. The same items are available from the same vendor, through eBay, at nearly a 50% price increase and still shipped from China. They are at https://www.ebay.com/itm/Industrial-...L/362662656311 and https://www.ebay.com/itm/TOPGNSS-RS2...O/273823871436. The USB puck is a TopGNSS GNSS200L, and the mushroom is a TopGNSS GN2000L.

These products might be available from other vendors, or not. They would likely not have the same model numbers, and may or may not have exactly the same features. Basically, all of the parts are available in China and can be assembled by different factories, or to different specs in the same factory, so great care is needed. There is no substitute for going over the specs with a fine-tooth comb, and even then some vendors may still send the wrong product. I'm afraid it is still the Wild West in Chinese electronics.

Greg

[RaymondR]

I have a couple of BU 353,s one of which would not work when I changed computers. They both looked exactly the same and it was not until I found a full set of specs that I discovered that they had changed the comms chip in the later purchased unit and I had to search and find a driver for the one fitted with the older chip.

So even within the same product they sometimes modify things.

The driver was sourced from the comms chip manufacturers web site and not the gps manufacturers.