General > General Technical Chat
GPS antenna question
<< < (3/3)
cdev:
They grab their ephemeris from the network even if there is no sim card. So it can still send an e911 location info if you make an emergency call which doesnt need a sim card. The reason a standalone, non networked GPS takes so long is it needs to download a table of expected orbital data into memory to work properly. That takes around 15 minutes.

People in North Korea using the Chinese cell network learned (this info is probably outdated) that if they kept their Chinese cell phone without its batteries in it, and then just put the batteries in and quickly called relatives in South Korea and then hung up right away, and removed the batteries, the old system the MSS had often could not locate people to be taken away to concentration camps. A few years ago they got a much more modern system to track down illegal cellphone users that works I suspect on TDOA, and its accurate to just a few meters. In this country where people are literally starving the government had stopping illegal international calling as their top priority, so they bought a system built its rumored by Rhode and Schwarz, which must have been sold to them by some 3rd party dealer, because of sanctions. Now all their cell phones, probably just like other countries, send their GPS locations, probably right away, due to AGPS. So they have multiple, redundant systems for locating illegal users of foreign telephone networks in their border areas.

----

A cell phone has access to the network so they now use AGPS, which basically means fetch the ephemeris over the network enabling an almost instant start.

If you dont pay for a data plan it still gets the ephemeris data and your GPS's location data is available to everybody else but you.

Will it fall back to downloading the ephemeris from the satellites when its not in range of a cell network? I don't know but I kind of doubt it. So dont count on using a cell phone GPS is you are a hiker, becuse as soon as you are over the hill from a cell phone site the GPS may stop working, (if the phone cant fall back to using the actual satellite ephemeris) either right away or in a day or two when the ephemeris data gets stale.

There should be a law requiring that GPSs natural functioning not be disabled for use by users by greedy cell phone companies.


-----

Yesterday I was surfing for some other reason and I noticed that Molex now sells compact helical GPS antennas. I dont know if they are QFH but it seems that they might be, if so they may be more likely to operate properly independently of any ground plane.

Sarantel used to make very good - very copact (tiny) ones but I remember hearing they are no longer in business. They are worth hunting down and using if you can find one.  But even if you can find one now it might be hard to find them in the future.

Similarly, if this is for a hobby use maybe you could find an old Vaisala aerosonde (QFH) GPS antenna. If you really want an GPS antenna that will work in almost any orientation, thats what I would pick. They are a full sized QFH for GPS which means two interwoven helical loops with a height or around 8 cm which fit in a cylinder with a diameter of around 3 cm.
Muku:
Thanks for reply cdev. I learned alot about GPS in general.

I thought of QFH antenna but I am making a tracker for my bike so which will mostly be used outdoors facing the sky. QFH are also little expensive. I am thinking of using one of those GNSS modules with attached patch antenna. There's one made by company called telit and they also have small form factor. Lets see how that will perform. I will let you know

Thanks
cdev:
A small patch antenna will probably work fine. You could also if you want, make a QFH antenna but if you do so make sure to use a blocking cap because a QFH being (two) loops will look like a short to any GPS that supplies power to an antenna. (Also protect the GPS's antenna input from ESD). A helical antenna is very easy to make and would work. I would just use a cheap puck antenna from ebay, whatever is acceptable cosmetically with the aforementioned tradeoffs.


--- Quote from: Muku on August 28, 2020, 09:13:56 pm ---Thanks for reply cdev. I learned alot about GPS in general.

I thought of QFH antenna but I am making a tracker for my bike so which will mostly be used outdoors facing the sky. QFH are also little expensive. I am thinking of using one of those GNSS modules with attached patch antenna. There's one made by company called telit and they also have small form factor. Lets see how that will perform. I will let you know

Thanks

--- End quote ---
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod