GPSTM and Lady Heather, display time 18 seconds off from NIST - Page 1
Forum section: electronics / testgear

author: tkamiya
author_rank: Super Contributor
timestamp: January 08, 2018, 06:38:43 pm
content: Can someone please help me with GPSDO with Lady Heather?My GPSDO is Nortel Trimble NTBW50AA, otherwise referred to as GPSTMLady heather is version 5.0Windows 10Serial port is USB basedThe issue is, the time Lady Heather (LH from here forward) displays is constantly off by 17 seconds. (give or take 1 second due to resolution) Comparison is made with NIST broadcast on the *net and it is always GPS time is ahead. (for example, LH may say 35 seconds past the hour and NIST may say 18 seconds after the hour) I thought of UTC offset but LH display shows "UTC ofs: 18".-tz is set to est5edt (time zone)-rx is blank for autodetect (GPS type)-rxx is not even mentioned (leap second offset)But LH is auto recognizing the machine type and picking up UTC offsets.I'm baffled.... especially because the error is double the offset value.

author: ArthurDent
author_rank: Super Contributor
timestamp: January 08, 2018, 07:02:57 pm
content: 18 seconds is the difference between UTC and GPS time to account for leap seconds. Switch to UTC time using Lady Heather commands.

author: tkamiya
author_rank: Super Contributor
timestamp: January 08, 2018, 07:13:50 pm
content: But, I don't want UTC displayed. I want my local time, and the config is so specified. From your comment, it sounds as if LH keeps corrected and uncorrected times, and display can reflect either of them.I think you are talking about timezone setting. I don't really see anything else. Would you mind giving me examples?

author: tkamiya
author_rank: Super Contributor
timestamp: January 08, 2018, 07:25:49 pm
content: I found it. TU command did it. Apparently, rather than configuring LH, it sends command go GPS itself to report in UTC time rather than GPS time.

author: ArthurDent
author_rank: Super Contributor
timestamp: January 08, 2018, 07:29:49 pm
content: You DO want UTC time displayed otherwise GPS time will display an 18 seconds difference as I have said. What you also want is a time zone correction to get to your local time zone. If I recall off the top of my head, type 'T' to get to the time menu and select 'U' for UTC and the 18 seconds difference will go away. Now type 'T' then 'Z' and enter '-5EST/EDT' or whatever to set the offset to your time zone. The documentation for Lady Heather explains this but you have to search for it. Check this YouTube video to see a leapsecond recorded at 00:00:00 UTC.

author: tkamiya
author_rank: Super Contributor
timestamp: January 08, 2018, 08:02:37 pm
content: and when I did TU, the very first line, far left icon changed from GPS to UTC.Thank you. I got it.

author: texaspyro
author_rank: Super Contributor
timestamp: January 08, 2018, 08:23:41 pm
content: The TZ (time zone) command converts the time from the GPS receiver to local time by adding the time zone correction to the receiver time.Many receivers can be configured to send either GPS time or UTC. GPS time and UTC time differ by the UTC offset (leapsecond count). The TG and TU commands configure what type of time to send (if the receiver does not support changing the GPS/UTC time that the receiver sends, Heather will do it in software by adding in the UTC offset (leapsecond) count). Which type of time that is being used is shown by the "GPS time OK" and "UTC time OK" message at the top left of the screen.Lady Heather can display UTC or GPS time (determined by the TU and TG commands) as local time (via the TZ command).

author: tkamiya
author_rank: Super Contributor
timestamp: January 08, 2018, 10:52:04 pm
content: Thank you. I discovered the TU command and that resolved my problem.