| Careyway | Posted: 3 Dec 2020, 11:26 PM |
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 Member Posts: 3 Joined: 3-December 20 |
Hi. My Precision Clock was purchased in July 2020 and initially worked OK taking about 6 or 7 hours for a GPS fix. I have not moved the clock at all, but now it does not seem to be able to get a GPS fix. On powering the clock, it starts to count up from zero and at some point several hours later, it show the correct time (to the nearest second!) The colon LED's and the rear LED on the PCB never blink as they should to show the clock is receiving a GPS signal. The clock is next to a south facing window and several other GPS devices (phone, Garmin etc) have no problem in getting a fix in this location. What should I do? ------------- |
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| mit | Posted: 4 Dec 2020, 12:32 PM |
 yeah whatever Admin Posts: 566 Joined: 4-May 16 |
Hi. It's possible the antenna or GPS module is damaged. I always recommend trying it outside (on battery power) because you never know if there's some interference or insulation effect indoors (I have a friend who lives in a modern tower block, and they have never been able to get GPS reception there - for any device). But I've noticed a handful (maybe 1% or 2%) of the modules simply don't work correctly. Maybe the antenna got knocked or damaged in shipping and moved the frequency peak. The cost of a new antenna, or even a new module, is low enough that it's worth a shot. I can strongly recommend using a u.fl to SMA adapter, and then a "magnetic puck" antenna on a long cable. I think I linked to it under the optional steps on the instructions page. Or, the active antenna from this thread is another good option. ------------- |
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| Careyway | Posted: 6 Dec 2020, 09:48 AM |
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Member Posts: 3 Joined: 3-December 20 |
Thanks, I will try your suggestions. Just one question, if the GPS module does not get a fix, how does the clock set the correct time? ------------- |
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| mit | Posted: 8 Dec 2020, 09:38 AM |
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yeah whatever Admin Posts: 566 Joined: 4-May 16 |
Every GPS satellite broadcasts the time, but at least four satellites are needed for a GPS fix. If the GPS module only has one or two satellites in view, it can still output the approximate time, but it won't be accurate because it can't compensate for the speed-of-light delay. The delay shouldn't be more than a few hundred milliseconds, but I've noticed that without a fix, the GPS modules tend to give up and drift by up to two seconds. Also, without the PPS signal present, the clock cannot sync properly to the messages, and the display tends to jitter as it constantly tries to adjust the time. ------------- |
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| Careyway | Posted: 11 Dec 2020, 11:52 AM |
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Member Posts: 3 Joined: 3-December 20 |
Hi. I tried putting the clock outside but still no blinking LED's after 8 hours. I found this active antenna - https://bit.ly/378d5kP from Rapid Electronics at only £2.12 each. I can confirm that this antenna works a treat on the GPS board as supplied with the clock. I get a fix in about 2 minutes and the colon LED's start blinking about 2 or 3 minutes after that. This is with the clock indoors in its normal place. So I assume that the supplied patch antenna was broken. Not sure how as it did work for a couple of months after I built the clock and it had not been moved. Anyway, all is good now and top marks to you for the excellent design & kit. Thanks. Last edit by Careyway at 11 Dec 2020, 07:40 PM ------------- |
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| mit | Posted: 11 Dec 2020, 04:47 PM |
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yeah whatever Admin Posts: 566 Joined: 4-May 16 |
Oh, excellent, glad you got it working. That's very cheap for an active antenna, I'll order a few for myself. At that price I could just bundle them in with the regular kit. Hmmm. Thanks for the update! ------------- |
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| rdavies6 | Posted: 6 Jan 2021, 01:55 PM |
 Member Posts: 2 Joined: 6-January 21 |
I was struggling to get a lock with the supplied antenna - not the antenna's fault, as I really wanted the clock indoors away from a view of the sky. I bought a couple of the ones mentioned from Rapid, and sadly the they failed to get a lock at all, even after 8 hours of sitting in a windowsill with a good view of the sky. Not exactly sure why I had problems…but I’m wondering if the u.fl connector wasn’t making contact with the centre pin? Rapid only had a few of these left (7, when I last checked), and they had reduced the price to £1.70 each...so maybe there's a relationship between the problems I had with them...and the price reduction? The antenna I did get success with however was a puck antenna with u.fl/sma adapter from Amazon (https://www.amazon.co.uk/dp/B00LXRQY9A) . I originally bought this to go with a Blitzortung Lightning detector I've just built, but I bought a second one to try with the clock...and I'm pleased to say it works perfectly, even sitting inside the house it maintains GPS lock. The Blitzortung receiver gives some GPS stats – so I can at least get a sense for how well the puck antenna sees the satellites (the puck was sitting on the floor next to my desk); I might dig out my Trimble GPS receiver, and run Lady Heather to get some more precise stats  ------------- |
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| mit | Posted: 6 Jan 2021, 03:39 PM |
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yeah whatever Admin Posts: 566 Joined: 4-May 16 |
Hi, thanks for sharing. I also bought one of those antennas from Rapid, and it didn't work for me at all either. However, one of the other antennas they sold, marked as 15dB gain, works fine. I suspect that the higher gain antenna is swamping the amplifier on the GPS module. This is also true of the 30dB active antenna I tried out last year. The magnetic puck antennas do seem to be the best option. If you have a serial adapter you can listen to the data from the uBlox module on the clock and using the u-centre software you can plot similar sky-view graphs. I can't remember if it gives a PPS accuracy estimate, that's a neat thing to have. ------------- |
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| rdavies6 | Posted: 7 Jan 2021, 02:31 PM |
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Member Posts: 2 Joined: 6-January 21 |
I don't have a FTDI Serial to USB board...but I did dig out an Expressif ESP32 board...so a couple of lines of code and I managed to capture the NEMA strings from the GPS board on the clock via the UART on the ESP32 board. I did try the u-centre software, but the UI seems to have been designed for a different brain to mine :)...so i stuck with the Lady Heather software from http://www.ke5fx.com/heather/readme.htm - screenshot attached with GPS coordinates redacted) ------------- |
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