Review by Mike Barrett

When we visited the Globalsat booth in CeBIT they had a number of new devices on display. One of these was the SD-502, an new updated SDIO based GPS receiver with onboard memory. It has taken a while, but this was launched in the UK at the PocketGPSWorld.com GPS Event at Basingstoke in November.

I have been putting the Globalsat GPS receiver through its paces over the last few months to see how it performs in "real life".

Overview

Globalsat launched the first SDIO based GPS receiver back in 2004. This was a great little GPS device, but it did have a couple of drawbacks. The main one was that the GPS had no memory so the maps and applications had to be stored in main memory.

Well Globalsat have listened to feedback and have produced a new receiver which includes 512Mb of memory onboard. Gone is the "Wings" of the antenna booster and it is replaced with a much more stylish designed package. Add in the super-sensitivity of the SiRFStarIII GPS chipset and you have a much more mature second generation SD GPS receiver.

So how does this all work out? It the GPS receiver as good as the well known Globalsat BT-338 Bluetooth GPS? Read on and find out...

The following specifications are from the Globalsat website:

Compatibility

The Globalsat SD-502 GPS receiver compatibility list (using the 1.32 software driver) is stated below. This list has been provided by Globalsat R&D. We have validated it to work with an XDAII and the HP iPAQ 4700. It does not work with the newer O2 XDA Exec/Orange M5000/HTC Universal/Qtek JasJar PDA.

The SD-502 SDIO GPS Review

It is difficult to review the Globalsat SD-502 without referring to it's predecessor the SD-501, but they are completely different. For starters the GPS chipset is the latest SiRFStarIII, then the antenna is a double helix, then of course the whole thing has a healthy 512Mb of memory.

Starting at the beginning the GPS has a new smart silver casing. There is a cover provided for the lower connector section of the GPS which protects the connectors from damage during storage. You will notice the absence of pictures of this cover here. I managed to loose mine!

At the top of the GPS is a black round tube. This houses the double helix antenna. All of this is implemented in a nice compact format that doesn't waste any space at all and is quite minimalistic.

The size of the exposed main body of the receiver is about the size of an SD card, plus half as much again for the antenna.

As the power for the SD-502 is taken from the host PDA there is no need for an on-board battery. This makes the GPS Receiver extremely light. With the power requirement of 90Ma there is only a small drain on the battery.

The SD-502 also sports a "double helix" antenna. What? I hear you ask. Well most GPS receivers use what is known as a patch antenna. From what I am told a patch antenna is pretty easy to tune and integrate. The double helix antenna on the other hand is much more difficult. You can see this to the right where the white tube is, the bands of copper and the tube form the antenna.

So why use the double helix then? Well the simple reason is that the patch antenna is good, but it only works well in one plane. i.e. the antenna needs to be pointing up at the sky. The double helix is not sensitive to position at all and, although slightly less sensitive than a patch antenna, will work well no matter what the orientation of the GPS is.

This is important for our usage models in PDAs as there is no telling how the PDA will be used. Indeed I will often have mine horizontal whilst walking but vertical in the car. Sometimes I have it vertical, but rotated into landscape mode. The double helix antenna copes with all of these positions well.

As you can see from the images to the right. my GPS came to pieces in my hands again... Well it did need a screwdriver as well, but is was a complete accident (honest!!).

It was almost not worth opening it up. There was little apart from the antenna to see. Most of the rest of the GPS receiver is heavily shielded. This of course is a good thing as it means that the weak and sensitive GPS signals are not affected by interference from other sources.

You can also see that the GPS is created using 3 modules: the connector; the GPS engine and the antenna.

Before you can use the GPS or the memory you need to install the driver on your PDA. I would recommend visiting the Globalsat download page and getting the latest version of the driver. It has been updated since the release of the product to market.

The driver is installed over activesync and once installed the GPS and memory will be visible. To actually see the GPS and memory you may need to perform a soft-boot on your PDA.

The memory is only available on the PDA, or on a PC through activesync. It is not possible to use it directly on your PC with a card reader. This means that transferring map data can take a long time to complete.

The Globalsat SD-502 in use

Initially I used the Globalsat SD-502 in my XDAII in the car. I used it to run both TomTom and Memory-Map (not at the same time of course). In fact all the applications I tried it with worked fine, as you would expect.

I also used it in my iPaq 4700. I used it in the car in both portrait and landscape modes and didn't notice any difference in the strength of the GPS fix. It was not quite as strong as the BT-338 but it was still more than adequate for accurate navigation.

As can be seen from the pictures to the right when in landscape mode the GPS is quite deep in the car, and close to the dash where all the noisy car electronics are. The GPS seemed to overcome this with minimal issues.

Time to fix was comparable with other similar SiRFStarIII GPS receivers. I normally had a fix before the navigation software had fully loaded.

The receiver showed the ability to retain a fix in all the environments I used it in. Admittedly I didn't test it in serious urban canyons, but I did keep my fix in an underground car park where there was just a few feet of open space to outside.

Now there is a feature of SiRFStarIII called static navigation or SN. SN when enabled prevents small movements in position from being reported. This is good for vehicle navigation as it stops the position jumping around when stopped in traffic. However if you are walking this can be a serious issue.

I needed to test this out whilst hiking. So off we went just after Christmas to the Brecon Beacons in South Wales for a short trip up Pen Y Fan to see what the SD-502 was like for hiking. As usual when I plan these sort of trips I cannot plan the weather. As usual we had some pretty poor weather as well.

The temperature that day was -5C but there was a stiff breeze blowing making it -20C with the wind chill factor in the more exposed places. I was wishing I had the insulation that my dog buster had... Despite the fact that Globalsat specify the operational temperature to go to -10C the wind chill did not seem to affect the GPS in any way.

As it was so cold and I was wearing fingerless gloves I needed to keep the PDA safe and my hands in my pockets (not a good idea on rough terrain). I found that the GPS frequently disengaged from the SD slot when it was in my pocket. This is not an issue with the design of the GPS per se, but more of a limitation of the technology. The SD slot is not designed to lock the device in. Therefore it is reasonably easy to disengage it.

The GPS performed perfectly. It was apparent that the Static Navigation was not enabled as the entire trip was logged smoothly and accurately. The power consumption was good. With the iPAQ 4700 fully charged at the start of the trip we walked for over 3 hours in the cold and still had over 50% battery remaining when we finished.

Roll mouse over image for portrait picture

The techies at Globalsat have come up with yet another winner with the SD-502. There are some issues with the underlying technology, but the GPS itself is well designed and a lot of thought seems to have gone into how the receiver will be used. It uses a double helix antenna which is a little less sensitive than the normal patch antenna, but the helix is capable of picking up signals in any position making it more flexible.

For PDA applications where the only slot available is SD and there is no Bluetooth this is pretty much the only available portable solution. With the addition of memory the SD-502 makes an excellent total navigation solution with storage for application, and maps whilst also providing the GPS data feed.

Pros

• SiRFStarIII sensitivity and accuracy
• Onboard memory
• Double Helix antenna

Cons

• Limited compatibility with PDAs
• No locking device on SD

References

Mike Barrett

www.Pocketgpsworld.com