[time-nuts] Navman T60-D125 GPS Timing Receiver Problems

Jay Flynn james.flynn at csun.edu
Tue May 26 23:11:29 EDT 2015


Many of the Navman T60-D125 units are floating around on various sales 
sites. Unfortunately, some come with built in problems and poor 
documentation.

Here are some things that I have found in working with one for the past 
year.

1) If you have found that communicating with the unit on the development 
board over the RS232 serial port is impossible, here is why: there is a 
flaw on the development board. 

When I bought my board, there was no communication to the unit. I 
thought the serial chip was bad and went to replace it. I discovered 
there is a serious flaw on the board. TX1 IN (PIN 11) is connected to 
TX2 OUT (PIN 7). It appears it should be connected to the pin opposite 
to it (PIN 10) which is TX2 IN. I removed the SP232 chip and cut the 
trace to Pin 7 (TX2OUT) under the SP232. Now the unit functions OK.

2) Some documentation mentions that the TU60-D120 (note 120 not 125 - 
there is no docs on the 125 out there) series is supposed to default to 
survey mode followed by position hold (best for time measurements).  
This does not occur with the unit I bought - a TU60-D125.  

You must put the unit into binary communication mode (@@Wb command at 
9600 8N1) and then use 1255 command to set it to survey mode and then 
onto position hold. You use this command to configure the unit as a 
TRAIM receiver. (By the way, when you use the @@Wb command to switch 
serial protocols, it will immediately start spitting out data.  Look for 
the 1056 message and it will tell you what mode the unit is in - and 
that survey mode on power up is DISABLED!!)
  
3) If you configure the unit with the 1255 command, it will NOT remember 
this configuration after power cycle - despite the function of the 1255 
command is supposed to do this.  So you need to do this each time you 
power up. That is, it will start out in the mode where it only responds 
to the @@XX commands and you must use @@Wb to switch over to the binary 
mode. And the use the 1255 command to command it into survey mode. After 
24hrs (or what ever time you choose) it will transition to position hold 
and work to specs.

I am comparing the output with a homebrew (yes, I mean it) WWVB receiver 
and getting delta F's comparing the 1PPS timing outputs of >1E-11 on 
average. 





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