[Scan-DC] Federal(?) spread spectrum system in 420-450 MHz in the DC area
Andrew Clegg
andrew_w_clegg at hotmail.com
Tue Jan 5 18:24:56 EST 2021
Chris and Greg,
Thanks for the feedback. That does sound like the system. They seem to have a fixed version of it set up in DC, because the signals are always there and always strong. It's interesting that the system (as described by Raytheon) is a tactical/battlefield system, yet there's one right here in DC.
If anyone's interested, there's a link below to a recording of the effect of the system on 440 MHz USB reception in Arlington. As the system frequency hops in and out of the receiver bandpass it creates a sudden amplitude disturbance that gets demodulated as a clicking noise. It sounds like it could be generic RFI, but the max-hold specan plot shows it's not (link below). The audio and screen captures were just acquired a few minutes ago.
Audio recording:
http://www.w4je.com/20210105_173904.wav
Max hold specan plot from 410-460 MHz (showing how the frequency-hopping system sweeps out six clearly-defined 5-MHz channels in 420-450 MHz):
http://www.w4je.com/N93XX_1.JPG
Non-max-hold plot. The frequency hopping of the system is evident in the waterfall plot:
http://www.w4je.com/N93XX_4.JPG
73 de W4JE
Raytheon web page on EPLRS:
https://www.raytheon.com/capabilities/products/eplrs
Enhanced Position Location Reporting System (EPLRS) | Raytheon<https://www.raytheon.com/capabilities/products/eplrs>
Enhanced Position Location Reporting System (EPLRS) EPLRS, the Army's Data Networking System for the digitized battlefield, provides the warfighter with the integrated network that supports warfighting systems and assures command control cycle superiority.
www.raytheon.com
________________________________
From: scan-dc-bounces at mailman.qth.net <scan-dc-bounces at mailman.qth.net> on behalf of Greg Danes <danesgswolf at gmail.com>
Sent: Saturday, January 2, 2021 1:19 AM
To: Chris Parris <lists at thefedfiles.com>
Cc: Scan DC <scan-dc at mailman.qth.net>
Subject: Re: [Scan-DC] Federal(?) spread spectrum system in 420-450 MHz in the DC area
I think that's exactly it.
https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.globalsecurity.org%2Fmilitary%2Fsystems%2Fground%2Feplrs.htm&data=04%7C01%7C%7C359718b02c8443608ca208d8aee6a178%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637451652854696561%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IhDY1tNUuAcECGNQOQeE6C%2BqSvVl0%2B7yjgyw%2BRGp5gQ%3D&reserved=0
On Fri, Jan 1, 2021 at 8:40 PM Chris Parris <lists at thefedfiles.com> wrote:
> Hi Andrew,
>
> I suspect that you might be seeing and hearing the Enhanced Position
> Location Reporting System (EPLRS). From the NTIA:
>
> > The military agencies use the band 420-450 MHz for the multi-function
> Position Location Reporting System (PLRS) and the modernized Enhanced
> Position Location Reporting System (EPLRS). EPLRS is a data communications
> network that enables the rapid determination of the locations of all units
> in the network. EPLRS also has communications and navigational capabilities
> in addition to the position location feature. The EPLRS and its airborne
> version, the AEPLRS, are critical to the operations and safety of our
> military forces
>
> It is from this document:
> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ntia.doc.gov%2Ffiles%2Fntia%2Fpublications%2Fcompendium%2F0420.00-0450.00_01MAR14.pdf&data=04%7C01%7C%7C359718b02c8443608ca208d8aee6a178%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637451652854696561%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ECvhStK8LFLBetFfWDiWaiuNbott1ic%2BGbw5pc%2BYQu0%3D&reserved=0
>
> - Chris
>
>
>
> > On Jan 1, 2021, at 9:04 AM, Andrew Clegg <andrew_w_clegg at hotmail.com>
> wrote:
> >
> > For several years, there has been a frequency-hopping spread spectrum
> system operating in the DC area across the entire 420 - 450 MHz band. That
> band is allocated on a primary basis to the federal government for
> radiolocation and on a secondary basis to amateur radio (the "440 band").
> Given the primary allocation status, and the persistence and coverage of
> this system, I presume this is a federal operation of some type. Does
> anyone know what this system is?
> >
> > From my QTH in Arlington, it's fairly strong. If I park my receiver on a
> 440 frequency, the spread spectrum system manifests as constant clicking
> noises as the system rapidly pops in and out of the frequency I'm tuned to.
> It's more noticeable in CW/SSB/AM modes than in FM mode. If I run a
> spectrum analyzer in max hold mode and let it build up for a minute or two,
> there's clearly five 6-MHz wide channels over which the frequencies hop. I
> don't know what the instantaneous bandwidth is; the system hops too fast
> for me to see that.
> >
> > I have heard the system while mobile driving up 95. I start to hear it
> ~20 miles south of the city, and it grows in strength as I get closer to my
> home QTH in Arlington. Other than driving up 95, I have not driven around
> the DC area to see where the signal is max strength.
> >
> > The signals complicate reception of weak signals in the 440 band,
> especially amateur satellite downlinks. I have not noticed any complaints
> from other local hams, but my antennas are in the clear and up high, so I
> may suffer more interference than some other hams do. I'm also not in much
> contact with local ham groups so if they're discussing this topic I may
> have missed it.
> >
> > I'm curious about what the system is and what it's used for. Does anyone
> know where the signal(s) originate from? Who else hears it at their QTH?
> >
> > 73,
> > W4JE
>
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