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StarGPS NX review

Posted by Iain Barker   04/04/2009 12:00AM

I was looking for a GPS solution on my NexStar SLT 'grab&go' scope, but something a little smaller and less expensive than interfacing to a hand-held GPS/PDA. Celestron have had their CN-16 GPS accessory on the market for a few years now, but I figure that technology moves on there might be other less expensive options on the market worth checking out.

A StarGPS NX unit looked like it might be a good choice for use with my Celestron mounts, and currently on sale is less than half the price of the CN-16 so worth a try. StarGPS is a small (less than 2 inches) 16-channel GPS adapter that is available with various cables to use with Meade AutoStar, Mac/PC, Celestron NexStar and others.

Out of the box, this has to be the easiest piece of hardware I have ever used - the setup was amazingly simple:

1/ Plug the longer cable into the bottom of the Nexstar handset
2/ Plug the shorter cable to the Aux port on the mount *
3/ Power on the mount

That's it!

A single LED on the GPS tells you the status: Solid at power up, long blink while it probes the scope type, and then one blink every two seconds to indicate GPS locked and data downloaded to the hand controller.

On a very wet and cloudly evening fortunately this is one telescope accessory that doesn't care about the weather, so I tested it on both my small Nexstar SLT and the larger C11 AS-GT (CG5-GT mount).

After getting the GPS lock, I went to "View Time-Site" on the Nexstar hand controller menu, and confirmed that the correct UTC time had been configured by the StarGPS. To check accuracy, I read the Lat and Long coordinates from the Nexstar SLT and typed them into Google Earth. The GPS lock was spot-on; literally within about 1 meter of where I was sitting while typing this.

Next I took the GPS to the other end of the house, in the attic where I have the CG5 mount. Again, the lock was spot-on, and the coordinates entered into Google Earth again placed it at the exact location (approx 25m from the previous test).

So what don't I like? Nothing too important, but there are a couple of things that could be better: Because the StarGPS uses the 9600 Baud RS232 interface, it has to connect to the bottom of the Nexstar hand controller rather than the 19200 Baud TTL 'Aux' ports on the mount itself. The cables are a little long, so might become an issue with cord wrap - especially since they are straight cables rather than curly-coils. The instructions suggest to run the cable inside the center of the handset curly-coil cable, but that just makes the handset less flexible so isn't an ideal setup.

But for the price and convenience, overall I am impressed - it does exactly what it says it would, and on sale at OPT for $121 plus shipping it's a bargain.


* A note on operational differences between the mounts:

The StarGPS worked the same on both my mounts, the only difference was that because the CG5 doesn't have an Aux port, an included RJ11 phone-style splitter is used to connect it in parallel to the hand control port.

The GPS only uses the TTL Aux port for drawing power; all signalling is done via the RS232 port of the hand controller in both cases.

RS232 support stems from the heritage of the StarGPS - it was originally designed to emulate a PS/2 style 'mouse', and if no telescope is detected after power it will default to operating as a 4800 Baud NMEA device over RS232 (so it can be hooked to a MAC/PC using an appropriate RS232 or USB cable).

Disclaimer: I wrote this review independently, the views are my own and I have no connection with either OPT Corp or the StarGPS manufacturer, other than being a happy customer.