Oct 28, 2015

New Radio Transmit Station Could Impact Interrogation Sites

The PIT Tag Steering Committee would like to pass on the following information from Gabriel Brooks, NOAA Fisheries, regarding a new source of radio interference that could be impacting interrogation sites with unshielded antennas. Please contact Gabriel (gabriel.brooks@noaa.gov) if you have any questions. 

Navy transmit station could impact unshielded antennas

Two weeks ago, while installing a site in northeastern California, Kyle Meier with West Fork Environmental noticed a significant noise source impacting the array.  With the help of a local contractor, they were able to confirm both the frequency (135.95kHz) and the direction, which at the time was to the south and west towards Sacramento.  After further research, Kyle determined the likely transmitter was a Navy transmission station in Dixon, CA.

NWFSC reached out to the contractor who operates the Dixon transmit station for the Navy.  They confirmed that this station, which has been dormant for several decades, was brought online as of 10/14/2015.  It appears that the modulated LF signal is impacting RFID sites throughout the west coast, from northern Washington to the Salmon River and south through Oregon and California.  In addition to impacting unshielded instream antennas, it now appears that the signal is also interfering with the Corner Collector at Bonneville.

This site will be broadcasting intermittently through mid-November.  It will begin broadcasting again in April 2016.  After consulting with the Navy, it is hoped that a second system being brought online simultaneously in April, but with a different frequency, will no longer impact RFID detection in the region.  We are currently working with the engineers involved to assess this second frequency and whether we feel it will negatively impact the readers. 

At this time, it is not possible to know when or for how long each transmission will occur.  However, it has been confirmed that on 10/17/2015 at 1322 PDT the transmitter shut off and resumed transmitting at 0736 PDT on 10/19/2015 for several hours.  Please check your sites for this timeframe to determine the impact.  It does appear that site and/or antenna orientation will vary the amount to which the LF signal is received.

The NWFSC will continue to receive updates from the Navy regarding the current testing timeline, and will disseminate that information as soon as it is made available.