Please note: GPS lock and frequency accuracy
Not sure if this is the right place to post this but I'd like to make people aware of an issue with the use of the GPS antenna (GPS puck).
Manual frequency measurements and other programs often rely on good (or near perfect) frequency stability of the KiwiSDR. One of the ways to achieve this accuracy from a KiwiSDR owner's perspective is to use the GPS puck that comes standard with it. The GPS puck will provide the KiwiSDR with signals that provide a 'GPS lock' for reliable frequency accuracy.
However, when clicking around the world map (linkfanel) of Kiwi SDRs there seem to be an awful lot of Kiwi SDRs that have no GPS lock, making these KiwiSDRs useless for specific frequency measurements. I am wondering if owners are aware of this?
I recently contacted one of the Kiwi SDR owners, and although he was using the provided GPS puck, he had no idea the GPS didn't lock. He connected the GPS antenna, placed it outside and thought that was enough. But the puck was facing south in the Southern Hemisphere and it wasn't picking up any satellites. After changing the puck to face a different direction, the problem was solved. It's usually as easy as that.
To check if your KiwiSDR is actually picking up any satellites, go to the admin panel and click on the GPS tab. You should see something like this when you click on the AZ/EI tab:
The list is showing a bunch of sat signals and the little round map shows a visual representation of the received satellites. If the list is empty (or near empty) and the map shows one or none, your KiwiSDR is not GPS locked. You can check it on the linkfanel site when you mouse over your pin as shows here. The bottom line tells us this KiwiSDR is GPS locked.
It needs to explicitly say: "GPS clock available: 30 fixes/min" the number can be different but the line should be there.
If the line is not present your KiwiSDR is NOT GPS locked.
It would be great if users could check their KiwiSDRs and make sure it's GPS locked. Sorry for the long post. Please let me know if you need help or if you have additional info or suggestions.
Comments
Well, okay. But this should hardly be news to anyone who has followed the forum for any length of time. We've discussed all these issues over the years in great detail.
There is a considerable influx of new KiwiSDR's recently. To help these new users, I figured a semi comprehensive write up about the issue might get some awareness and give some guidance. Hopefully this will help new users and older users to check if the GPS lock is actually working.
The GPS puck is designed to mounted on a car, so it has to be siting to a metal surface in order to have an adequate ground plane, and function correctly.
It doesn't need to be anything sophisticated, and something like a biscuit tin, or similar, is fine.
Almost anything will do, but it does help improve the polar diagram and overall sensitivity.
Regards,
Martin
Hi Martin, that is very useful. Thank you.
This is a typical data sheet for the type of ceramic patch used in the small GPS puck.
https://datasheets.kyocera-avx.com/ethertronics/AVX-E_1001039.pdf
Note the 70x70mm PCB ground plane used in the measurement test setup.
The 30x30 PCB inside the puck is really just a bit too small, and the polar diagram and off-axis noise rejection is improved by having a larger ground plane below it.
Many of the external GPS antennas are basically just the guts of a puck, mounted on a larger ground plane, and inclosed in a waterproof housing.
Regards,
Martin
Martin
Have you ever checked to see if there's a noticeable improvement in performance by pointing the 'main lobe' toward the equator? From that spec sheet it looks like there could be several dB of directivity available.
I've never checked to see.
Contrary to what many might believe, the GPS footprint is not uniform the world over. There is a scalloped footprint at each of the polls. Here in upstate NY, I can't even consider a northern only coverage antenna location as I sit in one of the nulls. You can view that on the admin/GPS page az/el graphic. Back in the beginning I could get my first Kiwi to lock as I simply put it out a Northern facing window. Here is the az/el display from one of my units showing the scalloped pattern.
I have not tried tilting the GPS antenna.
At my location, I get good coverage to the horizon, with the polar "hole" to the North, so I don't think I'd achieve much by tilting.
Regards,
Martin