Saturday, April 16, 2016

Is ANPOPS in Southern California?

It's long been assumed that the Rockwell Collins "ARINC UrgentLink" station using the 2G ALE address of ANPOPS is at or near the old ARINC headquarters in Annapolis, MD.  Perhaps it was at one time.

Lately, however, hundreds of ALE decodes have given a clear indication that it is most likely coming from somewhere in Southern California.

Let's look at some statistics. Here are the average S/N (as shown on PC-ALE) and the average frequency for the only stations audible at this QTH in SoCal:

Stn           S/N       Fq
010MDR    8.7    11206.2
103SCC    6.3    11300.3
104LKW    6.7    10559.3
105LAN     6.8     6792.7
ANPOPS    9.0    6163.0

As noted above, the sample on these is rather large.  It's over 50 normal sized pages of PC-ALE orderwire loggings. It includes a couple of all-night runs, to somewhat lessen the effect of diurnal band changes.  As far as I know, all of these stations are using very similar 125-watt radios with simple vertical antennas.

Note that ANPOPS actually averages a higher signal to noise ratio than the four other stations, all of which are known to be in the direct RF field at my location.  The only station whose average comes even close is 010MDR, Marina Del Rey, which is verified as coming from a business park only a few miles away from here.

ANPOPS also tends to be heard on lower frequencies.

Neither condition would support an origin in Maryland.  This result is simply not consistent with the known characteristics of recent transcontinental propagation. Band conditions have not been especially good, and genuine F2 skip from the eastern US has been weaker than normal.

And so we have something of a mystery, but then this system has been known for those.