Federal Mystery Frequencies

 A new federal mystery has appeared near my home base in the Portland, Oregon area. 

Over the past month I have begun hearing some odd radio traffic on an analog repeater on 173.1375 MHz. Sometimes the signal was weak but readable, and others it was very strong. The signal was always analog, with a CTCSS tone of 77.0 Hz. The audio was often an automated voice announcing warnings about voltage being low or being zero. 

At first I thought it might be something from the Bonneville Power Administration (BPA) as their radio system is still analog. But then the voice traffic seemed to be talking about the power system serving the repeater site, indicating there was a problem with the UPS power. 

I then begin to wonder if it was an image from a nearby amateur repeater site. I have a couple of ham repeater sites near me that sometimes cause images, but when I heard the traffic on 173.1375, I found nothing related on the VHF or UHF amateur bands. 

About two weeks ago, I manged to record a lot of voice traffic on this frequency. It was clearly a repeater and had beeps and boops when the users keyed up and finished talking. But there were no call signs or names mentioned while I was listening. The two users certainly sounded like Canadian truck drivers passing through the Portland area. There was discussions of traffic on I-5, various cars or drivers that were catching their attention, and eating plans, but nothing to identify the users. 

The truck drivers seemed to disappear, but the mystery deepened this last week when multiple VHF frequencies in the federal band were now all keyed up continuously with no voice and a 77.0 PL tone. The frequencies that are broadcasting full time are:

171.2750

173.1125

173.1375

173.6500

The frequency of 171.7875 MHz was heard at one time also keyed up but I can't confirm that one right now. 

What are these and why are they doing this? No information yet, but research is continuing - stay tuned!

UPDATE #1

I am confident that I located the 173.1375 MHz transmitter at the Willalatin Tanks radio site along Skyline Drive in Portland. I was able to pick it up with no antenna on the radio as I drove nearby. 

There is currently a Bonneville Power Administration radio site there, but also federal Integrated Wireless Network trunked system site (1-020) is there as well.

And I have noticed that the BPA is doing radio site upgrades at various locations on Oregon;

Marys Peak BPA Communications Site Project (DOE/EA-2050)

 www.bpa.gov

No jumping to conclusions just yet...