RESCUE 21 Sites in the Great Lakes

Electrical and electronic topics for small boats
jimh
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RESCUE 21 Sites in the Great Lakes

Postby jimh » Sat Mar 12, 2016 1:29 pm

A new article on RESCUE 21 sites is now available in the REFERENCE section. See

http://continuouswave.com/whaler/refere ... tions.html

This article discusses the new Coast Guard 21st-Century radio system known as Rescue 21. It documents my visits to five local installations and shows detailed photographs of the antennas, towers, and facilities. Unfortunately, I was not able to gain access to the receiver shacks, so I can't show you the actual gear in use, but I have drawn some quite reasonable inferences about the equipment based on the antennas and feedlines.

I have also created (in collaboration with another radio enthusiasts) a Google Earth mapping of almost all Rescue 21 sites in the Great Lakes of Superior, Michigan, Huron, and most of Erie.

jimh
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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Sun Mar 13, 2016 1:03 pm

A corollary topic to RESCUE 21 facilities is the accuracy of the direction-finding antennas and receivers. The accuracy will depend on the range from the transmitter to the receiver. The bearing to a transmitter comes from an advanced design digital direction finding antenna and receiver system. The accuracy of the system is rated to be 1-degree-RMS. The farther out on the bearing line from the receiver site, the more a 1-degree error increases, so the possible distance in error varies with range.

The antenna is a digital direction finding antenna and the bearing to the transmitter is determined by digital processing of the signals from multiple antennas in the antenna array. The antennas are mechanically fixed and are steered electrically. The digital signal processors work in parallel. Also, the accuracy of the antenna bearing varies with the mounting position of the antenna on the tower. Not every site has its direction finding antenna mounting in the best accuracy position. Mounting the antenna array atop the tower is believed to give better performance than side-mounting on the tower, but due to use of leased tower space, many sites employ side-mounted DF antennas.

A position is determined by getting two bearings on the transmitter from two receiver sites. The location of the transmitter relative to the two receiving sites also affects the accuracy. If the two bearing lines cross at 90-degrees, the position accuracy is best.

If a transmitter is 20-miles from the RESCUE 21 receiving location, a 1-degree error could mean an error of position of the transmitter of 2 x sin(.5) x 5280 x 20 = 1,840-feet.

If the other RESCUE 21 receiving site is farther away, say 30-miles, their 1-degree error could mean an error of position of the transmitter of 2 x sin(.5) x 5280 x 30 = 2,765-feet

If the bearings cross at a right angle, they make a box of uncertainty with 508,659-ft-sq, or an area of about 0.18-sq-mile.

The minimum signal duration for a bearing is very short, on the order of milliseconds. Of course, this depends if the receiver was already tuned to the transmitter's frequency or if it was in scanning mode, and on the direction finding mode being used. (There are several modes available. The USCG practice is to leave the primary array always tuned to 156.800-MHz or Channel-16, the distress hailing channel.) Other factors affecting accuracy are the signal strength, the nature of the path, the propagation conditions, and so on. Receiver sensitivity is rated to be very good, so bearings can be taken on signals that are quite weak (such as a signal from a 1-Watt transmitter whose antenna elevation is 2-meters and whose range to the site is 20-miles ).

jimh
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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Wed Apr 06, 2016 5:31 pm

I was reading the quoted text in my article about the distance of coastline covered by RESCUE 21, which says the sysem "is currently active along approximately 42,000 miles of coastline." I began to wonder if I had made an error in quoting that passage. I checked again and found there was no error. The original source says 42,000 miles of coastline is covered. This got me wondering how many miles of coastline there are in the USA. I found that according to NOAA there are 94,471 miles of coastline in the USA. NOAA comments about this:

As there is no reference that designates one specific shoreline as the "legal" shoreline, numbers for the length of the U.S. shoreline can vary depending on how the shoreline is defined.

The NOAA shoreline length calculation of 95,471 miles was determined by hand in 1939-40 with a recording instrument on the largest-scale charts and maps available at that time. Shorelines of outer coast, offshore islands, sounds, bays, rivers, and creeks were included to the head of the tidewater or to a point where tidal waters narrow to a width of 100 feet. For the Great Lakes, the shoreline lengths were measured in 1970 by the International Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data.

The total length of tidal shoreline includes measurements of the coastal states as well as the outlying U.S. territories and possessions.


Cf.: http://oceanservice.noaa.gov/facts/shorelength.html

jimh
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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Mon May 02, 2016 4:26 pm

It will be interesting to compare the accuracy of a position fix determined by radio-direction-finding methods receiving a transmission from a vessel with the accuracy of a position fix that could be discovered from the digital selective calling distress alert call transmitted from a vessel. As we saw above, at a typical distance from the radio-direction-finding array, and with the typical performance of the array receivers, the radio-directing-finder fix could be about 2,000 to perhaps 3,000-feet in error when determining the position of the vessel that is transmitting.

In comparison, a vessel sending its position from a GNSS receiver via DSC could transmit a position fix that was within about 30-feet of its actual location, if the vessel is using a good GNSS receiver and a modern Class-D or better DSC radio. In this comparison, the DSC distress alert position is much more accurate than the radio-direction-finder position fix.

It should be noted that older DSC radios which were only qualified to the USA requirement of meeting RTCM SC-101 recommendations (which were very popular in the USA beginning in c.2001 and were still being sold as recently as 2011) would transmit a distress alert with a position that was truncated to whole minutes of latitude and longitude. A minute of latitude is equal to 6,080-feet and a minute of longitude is COS(latitude)×6080-feet. This suggests that a DSC distress alert from on older DSC radio is likely to not be as accurate as the radio-direction-finder fix from a RESCUE 21 station. This is a non-intuitive result. Most people think their GNSS or GPS receiver is very accurate, which it actually is, but they do not realize that an old DSC radio only transmits a truncated position fix that could be a mile off.

For more about the limitation of using an older DSC radio qualified only to RTCM SC-101 recommendation, see my article at

http://continuouswave.com/whaler/refere ... sTest.html

Of course, a further problem for DSC vessel position is the tendency for many of these older radios to not have been connected to a GNSS or GPS receiver, so they would not be transmitting any position. And, even worse, since the operational practice of the RESCUE 21 system is to not monitor the DSC channel, if a vessel makes only a DSC distress alert transmission without any position or with the RTCM SC-101 truncated position, the RESCUE 21 system will never have a chance to get a direction-finding fix on that transmission (since it wasn't tuned to that channel).

peteinsf
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Re: RESCUE 21 Sites in the Great Lakes

Postby peteinsf » Tue Jul 26, 2016 3:35 pm

The thing I don't like about the Rescue 21 system is that all CG patrol traffic has relocated to the government portion of VHF and utilizes Project 25 (P25) digital voice. With that switch, VHF channels 21/22 has be resigned to only coordination with local government boats (or talking to the boat in distress [22])

When monitoring an actual rescue you now can't tell how far out the responding resources are unless you have a P25 radio and they happen to be in the non-encrypted mode.

My feeling is that during rescues, having the coast guard operating in a stealthy mode lowers the level of safety for the marine community. Coast Guard 9/11 thinking prevails...

Of course this is just an San Francisco area observation, maybe the Great Lakes are more open minded.

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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Mon Aug 01, 2016 8:50 am

The Coast Guard was moved into the administration of the Department of Homeland Security some years ago, and following that change there has been a corresponding change in the mentality and spirit of the organization. It seems to think and act more like a waterborne police force now, unlike its rich history as a lifesaving and service organization devoted to marine safety. When you get boarded for no good reason by some 19-year-old kid in black boots and automatic pistol and grilled for identification papers it's not your grandfather's Coast Guard any more. That they've moved all their routine radio traffic to private encrypted channels just reflects their own view of their new mission.

[Updated August 4] Project 25 radios for the Coast Guard were probably part of the Rescue 21 project. I think all government and municipal mobile radio systems are moving to a digital modulation scheme like P25. Having some standardization like P25 may allow for better inter-operation among services when responding to emergencies. And, digital modulation can provide encryption. These digital modulation schemes mean that the radio audio can be sent via ip-data-networks. I think the Department of Homeland Security has built their own national digital network for communications--which is probably another billion-dollar investment.

jimh
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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Thu Jan 19, 2017 10:32 am

peteinsf wrote:...When monitoring an actual rescue you now can't tell how far out the responding resources are unless you have a P25 radio and they happen to be in the non-encrypted mode.


Regarding the use of encryption with P25 radios, I recently listened to a TED TALK entitled "All your devices can be hacked" by Avi Rubin. He recounts reception of law enforcement traffic on P25 radio transmissions which were inappropriately sent without encryption. Compare at:

http://www.ted.com/talks/avi_rubin_all_ ... anguage=en

and the transcript at the 10:26 mark:

I'll show you two more. One is P25 radios. P25 radios are used by law enforcement and all kinds of government agencies and people in combat to communicate, and there's an encryption option on these phones....If you look closely at this device, it's got a switch for encryption or cleartext. Let me advance the slide, and now I'll go back. You see the difference? This is plain text. This is encrypted. There's one little dot that shows up on the screen, and one little tiny turn of the switch. And so the researchers asked themselves, "I wonder how many times very secure, important, sensitive conversations are happening on these two-way radios where they forget to encrypt and they don't notice that they didn't encrypt?"

So they bought a scanner. These are perfectly legal and they run at the frequency of the P25, and what they did is they hopped around frequencies and they wrote software to listen in. If they found encrypted communication, they stayed on that channel and they wrote down, that's a channel that these people communicate in, these law enforcement agencies, and they went to 20 metropolitan areas and listened in on conversations that were happening at those frequencies. They found that in every metropolitan area, they would capture over 20 minutes a day of cleartext communication. And what kind of things were people talking about? Well, they found the names and information about confidential informants. They found information that was being recorded in wiretaps, a bunch of crimes that were being discussed, sensitive information. It was mostly law enforcement and criminal. They went and reported this to the law enforcement agencies, after anonymizing it, and the vulnerability here is simply the user interface wasn't good enough. If you're talking about something really secure and sensitive, it should be really clear to you that this conversation is encrypted. That one's pretty easy to fix.


The whole TED TALK is available at http://www.ted.com/talks/avi_rubin_all_your_devices_can_be_hacked?language=en

jimh
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Re: RESCUE 21 Sites in the Great Lakes

Postby jimh » Sun Jan 29, 2017 2:30 pm

I added details about RFF ARCADIA to the reference article.

In the Fall of 2016 I visited the RESCUE 21 site at RFF ARCADIA. It was a small detour on our drive that day, and I couldn't miss the opportunity to visit another site. There was nothing unusual about this installation with the one exception: it seemed to be the only tenant on this leased private-operator tower. Again, the main article on RESCUE 21 can be found at

http://continuouswave.com/whaler/reference/Rescue21Stations.html


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