Best signaling devices from the searcher’s point of view - update

[CWK]

According to Ryan of Nautilus Lifeline:
“The frequency with which the signal is transmitted is based upon the ITU and FCC standards”

Which means?

The point that I was trying to make is that a PLB (such as the ResQLink) acquires GPS position once every 30 mins because it is a power draining exercise. The ResQLink keeps transmitting the same GPS position for 30 mins. Therefore I wonder how often the MRG acquires GPS positions. It can broadcast transmit every 4 or 5 mins, but I imagine that it would transmit the same GPS position for 30 mins just as the ResQLink does.

If you are drifting at 4 NM per hour, you could be 2 NM away from your last GPS fix.

 

[Dan]

I'll ask Ryan about the MRG frequency of GPS acquisition & transmission later.

 

[CWK]

It appears that PLBs use a 1695-MHz GPS position fix and battery drain is an issue.

From: http://www.cap-es.net/es electric technology/PLB GPS.pdf
It's no easy matter for a shirt pocket 24-hour signaling PLB to obtain an accurate 1695-MHz GPS position fix. The built-in GPS must offer exceptional sensitivity in order to receive the distant satellite signals, and develop that position fix without unduly draining the PLB 24-hour continuous duty power supply. Remember, even though the 5-watt UHF data burst only occurs for half a second, just under every minute the 121.5 MHz, 25-milliwatt locating signal for ground units is constantly tugging on battery capacity.

I do not know how GPS position is fixed by AIS based beacons but the SmartFind S10 AIS from McMurdo claims GPS position update every minute. See: https://www.mcmurdogroup.com/wp-content/uploads/2015/10/SmartFind-S10-datasheet-A4-iss1..pdf

 

[Dan]

It appears that PLBs use a 1695-MHz GPS position fix and battery drain is an issue.

From: http://www.cap-es.net/es electric technology/PLB GPS.pdf
It's no easy matter for a shirt pocket 24-hour signaling PLB to obtain an accurate 1695-MHz GPS position fix. The built-in GPS must offer exceptional sensitivity in order to receive the distant satellite signals, and develop that position fix without unduly draining the PLB 24-hour continuous duty power supply. Remember, even though the 5-watt UHF data burst only occurs for half a second, just under every minute the 121.5 MHz, 25-milliwatt locating signal for ground units is constantly tugging on battery capacity.

I do not know how GPS position is fixed by AIS based beacons but the SmartFind S10 AIS from McMurdo claims GPS position update every minute. See: https://www.mcmurdogroup.com/wp-content/uploads/2015/10/SmartFind-S10-datasheet-A4-iss1..pdf

In 2009 all those problem were fix and frequencies other than 406 MHz were phased out. Ignore any articles written older than 2009. Please review this presentation by NOAA (especially slide 12/26): http://www.sarsat.noaa.gov/UN_USA08/2009 USA Space Segment.pdf

 

[CWK]

In 2009 all those problem were fix and frequencies other than 406 MHz were phased out. Ignore any articles written older than 2009. Please review this presentation by NOAA (especially slide 12/26): http://www.sarsat.noaa.gov/UN_USA08/2009 USA Space Segment.pdf

Thanks. I think you have probably misunderstood the NOAA presentation.

Nothing in the NOAA presentation says that 1695-MHz GPS detection by PLBs was phased out. It says on p.12 that LEOSAR will not detect 121.5 MHz signals after 2009. According to Wikipedia (Emergency position-indicating radiobeacon station - Wikipedia): "Since 1 February 2009, only 406 MHz beacons are detected by the international Cospas-Sarsat SAR satellite system. ... In other words, Cospas-Sarsat has ceased satellite detection and processing of 121.5/243 MHz beacons. These older beacons are now only detectable by ground-based receivers and aircraft.

I think we can agree that PLBs transmit on 406 MHz to both LEOSAR and GEOSAR. I think we should be able to agree that PLBs also transmit on 121.5 MHz as a homing signal for SAR aircraft and that LEOSAR no longer detects these 121.5 MHz transmissions. Beyond this, things get a little confusing.

According to Wikipedia (Emergency position-indicating radiobeacon station - Wikipedia):
"There are two kinds of personal locator beacon (PLB):

• PLB with GPS data (internally or externally provided)
• PLB with no GPS data"

For PLBs with no GPS data, LEOSAR works out the location of the PLB through Doppler shift. See page 19 of the NOAA presentation.

PLBs with GPS data use 4 GPS satellites to determine their GPS position and transmit their GPS position to Leosar/Geosar on 406 MHz. See page 22 and 23 of the NOAA presentation. The NOAA presentation is silent on the frequency used by GPS satellites to transmit. Whatever frequency is used, PLBs have to detect these transmissions from GPS satellites in order to calculate or fix their GPS position. 1695-MHz is stated for this GPS fix in http://www.cap-es.net/es electric technology/PLB GPS.pdf

 

[Dan]

Thanks. I think you have probably misunderstood the NOAA presentation.

Nothing in the NOAA presentation says that 1695-MHz GPS detection by PLBs was phased out. It says on p.12 that LEOSAR will not detect 121.5 MHz signals after 2009. According to Wikipedia (Emergency position-indicating radiobeacon station - Wikipedia): "Since 1 February 2009, only 406 MHz beacons are detected by the international Cospas-Sarsat SAR satellite system. ... In other words, Cospas-Sarsat has ceased satellite detection and processing of 121.5/243 MHz beacons. These older beacons are now only detectable by ground-based receivers and aircraft.

I think we can agree that PLBs transmit on 406 MHz to both LEOSAR and GEOSAR. I think we should be able to agree that PLBs also transmit on 121.5 MHz as a homing signal for SAR aircraft and that LEOSAR no longer detects these 121.5 MHz transmissions. Beyond this, things get a little confusing.

According to Wikipedia (Emergency position-indicating radiobeacon station - Wikipedia):
"There are two kinds of personal locator beacon (PLB):

• PLB with GPS data (internally or externally provided)
• PLB with no GPS data"

For PLBs with no GPS data, LEOSAR works out the location of the PLB through Doppler shift. See page 19 of the NOAA presentation.

PLBs with GPS data use 4 GPS satellites to determine their GPS position and transmit their GPS position to Leosar/Geosar on 406 MHz. See page 22 and 23 of the NOAA presentation. The NOAA presentation is silent on the frequency used by GPS satellites to transmit. Whatever frequency is used, PLBs have to detect these transmissions from GPS satellites in order to calculate or fix their GPS position. 1695-MHz is stated for this GPS fix in http://www.cap-es.net/es electric technology/PLB GPS.pdf

I’m confused on what you are trying to say. First of all you are referring to a 12 years old (2006) article. There are a lot of changes / improvements / fixes in UHF transmission technology since.

I read the PLB1 manual many times & could not find any reference of 1675 MHz being used for “fixing” GPS location. There are only 2 frequency bands mentioned in the manual:
1. 406 MHz for satellite transmitter
2. 121.5 MHz.for homing beacon.

As far as 1695 MHz, it is used for the Geosynchronous Operational Environmental Satellite (GOES) meteorological satellites, not SAR satellites (LEOSAR or GEOSAR). GOES satellites use this frequency to transmit weather & other meteorological data, not for Search And Rescue operation.

https://www.ntia.doc.gov/files/ntia/publications/compendium/1675.00-1695.00_01SEP14.pdf

“The Geostationary Operational Environmental Satellites (GOES) series of satellites operate in this band transmitting weather and other meteorological data to earth station receivers for further processing and distribution. In addition, Federal agencies use the 1675-1683 MHz portion of this band to transmit meteorological data from radiosondes to ground stations for weather forecasting.”

 

[CWK]

I’m confused on what you are trying to say. First of all you are referring to a 12 years old (2006) article. There are a lot of changes / improvements / fixes in UHF transmission technology since.

I read the PLB1 manual many times & could not find any reference of 1675 MHz being used for “fixing” GPS location. There are only 2 frequency bands mentioned in the manual:
1. 406 MHz for satellite transmitter
2. 121.5 MHz.for homing beacon.

As far as 1695 MHz, it is used for the Geosynchronous Operational Environmental Satellite (GOES) meteorological satellites, not SAR satellites (LEOSAR or GEOSAR). GOES satellites use this frequency to transmit weather & other meteorological data, not for Search And Rescue operation.

https://www.ntia.doc.gov/files/ntia/publications/compendium/1675.00-1695.00_01SEP14.pdf

“The Geostationary Operational Environmental Satellites (GOES) series of satellites operate in this band transmitting weather and other meteorological data to earth station receivers for further processing and distribution. In addition, Federal agencies use the 1675-1683 MHz portion of this band to transmit meteorological data from radiosondes to ground stations for weather forecasting.”

Look at it this way. The manuals onlybdeal with PLB TRANSMISSION. It is true that PLBs only transmit in 406 and 121,5 MHz.

BUT PLBs with GPS also have to RECEIVE transmissions from GPS satellites in order to ascertain its GPS position. GPS satellites do not use 406 or 121,5 MHz.

 

[Dan]

Look at it this way. The manuals onlybdeal with PLB TRANSMISSION. It is true that PLBs only transmit in 406 and 121,5 MHz.

BUT PLBs with GPS also have to RECEIVE transmissions from GPS satellites in order to ascertain its GPS position. GPS satellites do not use 406 or 121,5 MHz.

I got it know. I always thought that the doppler shift by several LEOSAR triangulation would also provide the GPS location of where the PLB 406 MHz distress signal & feed that GPS info to the MCC & GEOSARs. So, what you are saying is that a separate transmission would be sent by the PLB to GPS also in order to get GPS position before transmitting the whole distress alert package to LEOSARs & GEOSARs, sort of redundancy GPS info.

Based on this: GPS signals - Wikipedia “...In the case of the original GPS design, two frequencies are utilized; one at 1575.42 MHz (10.23 MHz × 154) called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2...”, which is not 1695 MHz.

 

[CWK]

I got it know. I always thought that the doppler shift by several LEOSAR triangulation would also provide the GPS location of where the PLB 406 MHz distress signal & feed that GPS info to the MCC & GEOSARs.

Oh great! You understand triangulation.

There are at least 4 GPS overhead at any point on earth with GPS coverage. This means that there are lots of GPS satellites in total. Your PLB needs to see 3 GPS satellites in order to triangulate your position. According to the NOAA presentation Pg. 23, "Minimum of 3 satellites needed to compute locations. Additional satellites improve accuracy."

So, what you are saying is that a separate transmission would be sent by the PLB to GPS also in order to get GPS position before transmitting the whole distress alert package to LEOSARs & GEOSARs, sort of redundancy GPS info.

Lets try and keep this simple. Think of transmitting as speaking. Then think of receiving as hearing.

Your PLB1 user manual says, "Warning : As testing the GPS receiver expends significant amounts of battery energy do not test the gps operation more than oncea year."

I don't think your PLB transmits to the GPS satellites. I think the GPS satellites transmit a signal that your PLB has to receive. Your PLB1 manual refers to the GPS receiver.

Your PLB receives (hears) transmissions from GPS satellites. Based on this, it calculates your GPS position by triangulation. Your GPS position is then transmitted by your PLB to LEOSAR/GEOSAR on 406MHz.

Based on this: GPS signals - Wikipedia “...In the case of the original GPS design, two frequencies are utilized; one at 1575.42 MHz (10.23 MHz × 154) called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2...”, which is not 1695 MHz.

Your PLB1 manual says:
"GPS Receiver (rescueME PLB1 only)
Satellites Tracked. . . . . . . . . . . . . . . . . . . . . . . . . . .66 Channel"

Wikipedia says that there were 2 frequencies used in the original design of GPS. Your PLB1 tracks 66 channels. If each channel is tuned to one frequency, there could be a number of different frequencies currently used by GPS satellites. I don't know what those frequencies are.

 

[Dan]

....I always carry a reef hook which can be used to leash people together if required so I don’t feel the need for a dedicated leash...

This is a very good idea! Thanks for mentioning it. Your comment made me reconsider carrying reef hook instead of a leash+carabiners kit.

Last December I was in Bali after returning from Raja Ampat & saw a nice reef hook with 5’ plastic coated coiled wire & clips on both ends of the coiled wire for $15 in one of dive shops in Denpasar. I bought it & tested it in Palau a few weeks later in Peleliu Cut & Blue Corner. It works great & it’s pretty compact kit. So, I decided to replace my leash+carabiners kit (as shown in the left side of the picture, below) with the reef hook (as shown in the right side of the picture, below). Now my right BCD pocket is less congested.