FYI - GPS

VK3KYY
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Re: FYI - GPS

Post by VK3KYY » Mon Jan 02, 2023 12:17 am

Which pin is the Backup voltage?

I think it would be better if it was possible to fit a small backup battery.

CU7AAZ
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Re: FYI - GPS

Post by CU7AAZ » Mon Jan 02, 2023 12:32 am

What I intended with the post was to know if it was possible to increase the speed of the GPS modem. To acquire satellites faster
I know the hardware isn't the best. I already bought a new antenna for the gps.
I'll install it when it arrives, and then I'll share the results
Thanks

VK3KYY
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Location: Melbourne, Australia

Re: FYI - GPS

Post by VK3KYY » Mon Jan 02, 2023 12:37 am

CU7AAZ wrote:
Mon Jan 02, 2023 12:32 am
What I intended with the post was to know if it was possible to increase the speed of the GPS modem. To acquire satellites faster
I know the hardware isn't the best. I already bought a new antenna for the gps.
I'll install it when it arrives, and then I'll share the results
Thanks
Although the antenna is not good. I think the GPS would be much better if it did not always need to perform a full scan / "cold start"

I have some external GPS modules which I connect to the MD-9600 and they get a fix much quicker because they contain a backup battery, so do not need to do a cold start

UA0LMC
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Re: FYI - GPS

Post by UA0LMC » Mon Jan 02, 2023 4:05 am

VK3KYY wrote:
Mon Jan 02, 2023 12:17 am
Which pin is the Backup voltage?

I think it would be better if it was possible to fit a small backup battery.
Pin 6 (yellow dot on GPSr). And the other yellow dot is +3.3V when the radio is on.
I got about 8uA backup current (datasheet claims 10uA typical) - so the same type as CPU RTC backup battery should suffice for a few days.

But you need to perform the rest of the mod to disconnect LNA power supply from Vbackup pin and to make the reset pin floating as it's in Vbackup power domain - but connected to Vcc via resistor.

Now I'm thinking about using a plain old resistor divider from the radio's main battery - it's cheap and simple, and 50-100uAmps should not drain the battery too quick. However, I have not tested it yet.

VK3KYY
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Location: Melbourne, Australia

Re: FYI - GPS

Post by VK3KYY » Mon Jan 02, 2023 5:32 am

UA0LMC wrote:
Mon Jan 02, 2023 4:05 am
VK3KYY wrote:
Mon Jan 02, 2023 12:17 am
Which pin is the Backup voltage?

I think it would be better if it was possible to fit a small backup battery.
Pin 6 (yellow dot on GPSr). And the other yellow dot is +3.3V when the radio is on.
I got about 8uA backup current (datasheet claims 10uA typical) - so the same type as CPU RTC backup battery should suffice for a few days.

But you need to perform the rest of the mod to disconnect LNA power supply from Vbackup pin and to make the reset pin floating as it's in Vbackup power domain - but connected to Vcc via resistor.

Now I'm thinking about using a plain old resistor divider from the radio's main battery - it's cheap and simple, and 50-100uAmps should not drain the battery too quick. However, I have not tested it yet.
Its a bit of a hack, but if the GPS consumes 8uA, and highest battery voltage is 8.4V when charged, then a 680k from the supply to that pin will give 7.5uA

UA0LMC
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Location: Vladivostok, Russia

Re: FYI - GPS

Post by UA0LMC » Mon Jan 02, 2023 5:41 am

VK3KYY wrote:
Mon Jan 02, 2023 5:32 am
Its a bit of a hack, but if the GPS consumes 8uA, and highest battery voltage is 8.4V when charged, then a 680k from the supply to that pin will give 7.5uA
Not sure if the current value is constant enough. But something like 100k+68k divider looks legit. Maybe I'll test it later.
The other way is to use a micro-power LDO, something like HT7133.

UA0LMC
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Re: FYI - GPS

Post by UA0LMC » Sat Jan 07, 2023 1:51 pm

ve7mdt wrote:
Sat Jan 07, 2023 12:06 am
UA0LMC wrote:
Mon Dec 19, 2022 7:12 pm
ve7mdt wrote:
Thu Oct 20, 2022 4:17 pm
I think the 24 GPS satellites (except the WAAS special purpose ones) fly in all kinds of paths in space and thus no need to orient it toward "north" from the southern hemisphere. It should work globally and thus the namesake.
Nope.
GPS orbital plane inclination is 55 degrees - so for 40-ish degrees latitude most of the satellites are to be found somewhere more or less towards the equator.
Also there is a bunch of QZSS and GEO/GSO BeiDou satellites visible here in Asia/Australia - which are again located more or less towards the equator.

It should not be a big problem when you have a decent GPSr/antenna - but not in the case of RT3s though.
https://www.faa.gov/about/office_org/he ... %20regions.

How did you jump from the 55 deg inclination orbital planes to conclude that the GPS does not cover the earth completely? Look at this webpage, it says that exactly because of the 55 deg inclination orbital planes of the sats, the both polar regions are covered! You are completely wrong in this.
I'm not saying there are no sats towards the pole - I'm just saying there are more satellites towards the equator most of the time.
So heading the antenna somewhere towards the equator (as opposed to heading it towards the pole) will most probably (but not necessarily) lead to an easier signal acquisition under restricted conditions, such as partially-obstructed sky view and poor GPS antenna performance.

See attached picture. It's for my QTH (I'm in northern hemisphere), the time is about 40 minutes ago.
Screenshot 2023-01-07 at 23-09-34 GNSS View.png
Screenshot 2023-01-07 at 23-09-34 GNSS View.png (74.67 KiB) Viewed 2025 times
You may play with https://app.qzss.go.jp/GNSSView/gnssview.html for your location.
Select the masking angle of 5 degrees (pretty modest for on-the-ground receiver) and disable the Glonass and Galilleo constellations which are not supported by RT3s GPSr.

OE1MWW
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Re: FYI - GPS

Post by OE1MWW » Sat Jan 07, 2023 3:07 pm

interresting finding.
In Vienna / Austria (48,269N 16,385E) I see a even distributed number of Sats in the nothern and southern hemisphere.
As I looked towards the equator, South is on top. ;-)
73s Wolfgang OE1MWW
Attachments
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CU7AAZ
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Location: Azores

Re: FYI - GPS

Post by CU7AAZ » Mon Jan 23, 2023 11:04 pm

Hello everybody!
Finally!
New GPS antenna installed. Excellent results!
28db antenna, installed on top of the radio.
When activating the gps, in one minute the gps starts to receive the satellites.
Amazing, I wasn't expecting it. Indoors, he obtained 9 satellites. (And with the exact location of my house)
It took a lot of work but I'm happy with the result.
73s everyone
CU7AAZ
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VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: FYI - GPS

Post by VK3KYY » Tue Jan 24, 2023 3:29 am

Thanks for sharing

Personally I think a separate external GPS module is better, because the GPS modules normally contain a small battery to maintain the backup memory in the GPS module, so that it can perform a warm start, whereas the internal GPS does not have such a battery and always has to perform a cold start

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