Trimble Lassen SK8 GPS Receiver

Hi.

I have one of these up and running with TSIPchat. - Took a while but I got there.

The system appears to be working ok. I can talk to it and get messages back from it.

The problem is it's miles out in it's reported GPS fix. Is there something I need to do to get the position correct?

I have attached a snap shot.

Can nayone help please.

Regards - Paul

OK I'm an idiot! - There's a difference between GPS co-ordinates and LAT LONG co-ordinates. Doh!

Next step is to get all this data to a PIC convert it to RTTY and transmit it via a radiometrix module... A self positioning GPS RTTY beacon. Why?- no idea just seems like fun.

Regrads - Paul

I reckon it puts you in the north Derbyshire peak district, just south of Huddersfield. However I see you are posting from Birmingham. Hmmm!
To convert lat & lon to Northern and Eastings, you need to put these values through the Transverse Mecarter Projection which is mathematically complex. However I have the source code in C if interested. It took a 68HC11 micro running at 8MHz nearly 4 seconds to do the conversion. On a PC it won't be a problem.

**broken link removed** may help.

I used the lassen about 20 years ago and don't remember any specific issues with it.

There is no difference between GPS co-ords and Lat & Lon that will give you such a difference. You may want to look at switching off any differential GPS offset that may be causing this offset before you got it.

The Rockwell GPS Navcore V engine circa 1990 used it's own floating point IEEE standard for the maths, but after conversion, it still was spot on here in the UK.

I made my first GPS car alarm using the Navcore in the early 90's and a paging transmitter to send it's co-ords. I still have it in the loft for nostalgia reasons and to remind me I could have beat Tom Tom...but didn't as I am crap at marketing.

Hi.

I realised that the Lassen is sending co-ords in GPS format. When you do the conversion it does place it absolutely spot on to the antenna in my back garden. I wont bother converting in the pic as i'll just cut & paste the coordinates into a PC conversion before overlaying in google maps.

I have the prototype up and running now. I have just spent tonight doing the PCB print ready to etch the weekend.

Prototype video is here - https://www.youtube.com/watch?v=wpUeo6ZFPFk

Regards - Paul

Depends on if the transmitter antenna is horizonantaly or vertically polarized. Ground Plane is a vertically polarized antenna; Dipole is horizontally polarized.



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