What is "Line A" protecting?

[AE5KA]

I've searched around a bit, but I haven't found an answer. What is the 70cm quiet zone along the US-Canada border protecting? I answered the question correctly on the exam, but haven't been able to find the rationale for it.

Thanks

[KB1LKR]

Likewise, Line C in Alaska adjacent to the Canada border, and lines B (in Canada near continental US) and D (in Canada, near Alaska).

I always assumed that Industry Canada (or other) allocated 420-430 MHz to a differant service, apparently land mobile, than US NTIA & FCC do, hence Line A (and lines B, C, & D) form a buffer zone to mutually protect users on both sides from interference from the other side of the border. See: http://www.fcc.gov/oet/info/maps/canline/canline.html for a nominal map

I guess the $64 (US dollars?) question is what is/are the primary (& secondary) allocation(s) in CA in that frequency range. on the US side it is primarily government (PAVE PAWS phased array radar) and secondarily amateur.

US GMRS (part 95) is also limited in power North of A and East of C.  
       

[KB3PXR]

In Canada the range of 420-430 MHz is used for the Land Mobile radio service. Also there are some licenses in the US for the Private Land Mobile radio service north of Line as these frequencies cannot be used for Amateur service. I however do not see the sense in that because the Canadian government does not allow Land Mobile below Line B. The area between Line A and Line B (as well as Line C and Line D) are supposed to be dead zones on that range to prevent interference to the radio services that use those frequencies in either the US or Canada.

[N2IK]

By treaty,all frequencies within the Line A area must be coordinated both by US and Canada. On the amateur frequencies, the relevant frequency coordinators work with each other on both sides of the border to mutually coordinate frequencies. This is similar to frequency coordinators checking with adjacent coordinators if locations are close enough to territory boundaries.

73 de Walt N2IK

[AC0HK]

"What is "Line A" protecting?"

From the ARRL Repeater Directory: "The band (420-450MHz) is shared by amateurs with government Radio Location Services (RADAR); amateurs must not interfere with these priority government stations."

Here is an example of the type of government radar installation that "Line A" is possibly designed to  protect:

http://en.wikipedia.org/wiki/Cavalier_Air_Station

Elsewhere on the internet I found the following:

"PARCS is located at Cavalier Air Force Station (AFS), in Cavalier, North Dakota, near the Canadian border. It is a north-facing phased array radar used for ballistic missile tracking and detection, providing warning information on any missiles launched over the polar region directed at the CONUS. In conjunction with its missile warning function, PARCS performs a corollary duty of space warning for the SSN. The radar can detect targets within a volume of 140 degrees azimuth and an elevation scan of approximately 93 degrees. Also known as the AN/FPQ-16, PARCS operates in the 420-450 MHz region of the UHF band at a maximum power of 14.3 megawatts. Average output power is 715 kilowatts.

[AE5KA]

Thanks, makes sense to me.