Decreasing number of used satellites

Hi all,

I am using a Garmin GPS 24xd HVS with gpsd 3.17.

The GPS does not move. I observe that the number of used satellites sometimes decreases over time although there are many satellites visible. As an example the used satellites continuously decreased within 6 hours from around 12 satellites to 2.

Why are satellites tagged with “used”: false although they have a good ss value?

Is there any known issue around this with gpsd 3.17?

Here is an example of the SKY message with 2 used satellites although 15 satellites are visible:

{

"class": "SKY",

"device": "/dev/ttyS0",

"vdop": 0.79,

"hdop": 0.60,

"pdop": 1.00,

"satellites": [{

"PRN": 8,

"el": 36,

"az": 293,

"ss": 41,

"used": true

}, {

"PRN": 10,

"el": 50,

"az": 138,

"ss": 40,

"used": false

}, {

"PRN": 16,

"el": 50,

"az": 192,

"ss": 45,

"used": false

}, {

"PRN": 18,

"el": 23,

"az": 62,

"ss": 44,

"used": false

}, {

"PRN": 21,

"el": 16,

"az": 246,

"ss": 26,

"used": false

}, {

"PRN": 23,

"el": 50,

"az": 83,

"ss": 40,

"used": true

}, {

"PRN": 26,

"el": 23,

"az": 177,

"ss": 32,

"used": false

}, {

"PRN": 27,

"el": 78,

"az": 301,

"ss": 48,

"used": false

}, {

"PRN": 71,

"el": 9,

"az": 11,

"ss": 35,

"used": false

}, {

"PRN": 72,

"el": 33,

"az": 56,

"ss": 41,

"used": false

}, {

"PRN": 78,

"el": 32,

"az": 221,

"ss": 39,

"used": false

}, {

"PRN": 79,

"el": 44,

"az": 291,

"ss": 44,

"used": false

}, {

"PRN": 81,

"el": 38,

"az": 279,

"ss": 41,

"used": false

}, {

"PRN": 87,

"el": 29,

"az": 68,

"ss": 39,

"used": false

}, {

"PRN": 88,

"el": 69,

"az": 19,

"ss": 40,

"used": false

}

]

}

Thanks!

Ulrich

Ulrich Wielant
LEONARDO Germany GmbH
Embedded Systems

Raiffeisenstrasse 10 - 41470 Neuss - Germany
Tel. +49 (0) 2137 782-216 Fax +49 (0) 2137 782-11
u.wielant@leonardogermany.com
www.leonardogermany.com

From:	Wielant, Ulrich
Subject:	Decreasing number of used satellites
Date:	Fri, 10 Jun 2022 12:15:18 +0000