[Scan-DC] 401.25 MHz DORIS beacon coming from Goddard or somewhere else?

Wed Mar 31 17:01:29 EDT 2021

Interesting. Thanks for trying Joel. I think without CW or SSB mode, the signal might be hard to hear.

For those who are interested, here is a waterfall plot of the RF spectrum:

http://www.w4je.com/doris.bmp
[http://www.w4je.com/doris.bmp]
The x-axis is frequency, running from 401.190 to 401.310 MHz (center = 401.250, span = 120 kHz). The y-axis is time, spanning about 35 seconds. You can see the data bursts from the DORIS signal every ten seconds.

Here is a 12-second audio recording, capturing two data bursts. This is in CW mode with a pitch frequency of 1 kHz and an audio filter bandwidth of about 500 kHz total:
http://www.w4je.com/doris.wav

Here is an image of the audio frequency water fall plot, spanning about six seconds, showing one audio burst with modulation sidebands around +/-200 Hz:
http://www.w4je.com/doris-af.bmp
[http://www.w4je.com/doris-af.bmp]

These were captured with HDSDR using the IQ output of an ICOM R8600.

Another interesting aspect is that I see doppler-shifted tones traversing the audio spectrum on a regular basis, typically one every two or three minutes. Are these reflections of the DORIS signal off planes? Or are these satellite signals downlinking at 401.25 MHz? If the latter, it's a lot of satellites. Here's an example (not the strongest doppler-shifted signal, but not the weakest):
http://www.w4je.com/doris-af-doppler.bmp
[http://www.w4je.com/doris-af-doppler.bmp]

73,
Andy
W4JE

________________________________
From: Joel Kahn <jrkahn at att.net>
Sent: Wednesday, March 31, 2021 4:04 PM
To: Andrew Clegg <andrew_w_clegg at hotmail.com>; Scan DC <scan-dc at mailman.qth.net>
Subject: Re: [Scan-DC] 401.25 MHz DORIS beacon coming from Goddard or somewhere else?

Andy,

I punched the frequency 401.250 into my HP-I and have had raw data running for 1/2 hour. All I am hearing is static. No CW or other intelligible noise. I am  about 5'ish miles from Goddard, just over PG line into Montg Co.

Joel R Kahn

On Wednesday, March 31, 2021, 10:14:24 AM EDT, Andrew Clegg <andrew_w_clegg at hotmail.com> wrote:

Thanks Dewey. I tried to find a local online SDR that covers the 400 MHz band, but I was unable to find such a resource.

________________________________
From: scan-dc-bounces at mailman.qth.net<mailto:scan-dc-bounces at mailman.qth.net> <scan-dc-bounces at mailman.qth.net<mailto:scan-dc-bounces at mailman.qth.net>> on behalf of Dewey <dewey3 at gmail.com<mailto:dewey3 at gmail.com>>
Sent: Wednesday, March 31, 2021 8:58 AM
To: Scan-DC at mailman.qth.net<mailto:Scan-DC at mailman.qth.net> <Scan-DC at mailman.qth.net<mailto:Scan-DC at mailman.qth.net>>
Subject: Re: [Scan-DC] 401.25 MHz DORIS beacon coming from Goddard or somewhere else?

Greetings Andy!

I just checked using SDRSharp with a NooElec SMArt RTL-SDR dongle and the
Airspy Mini, and punched the frequency into the 536, all on the outside
antenna, and not getting anything near the PG/Charles County line along the
Maryland shore line.  So given our locations, I would say that your thought
about it coming from Goddard is probably accurate.

Dewey

-----Original Message-----
From: scan-dc-bounces at mailman.qth.net<mailto:scan-dc-bounces at mailman.qth.net> <scan-dc-bounces at mailman.qth.net<mailto:scan-dc-bounces at mailman.qth.net>> On
Behalf Of Andrew Clegg
Sent: Wednesday, March 31, 2021 08:44
To: scan-dc at mailman.qth.net<mailto:scan-dc at mailman.qth.net>
Subject: [Scan-DC] 401.25 MHz DORIS beacon coming from Goddard or somewhere
else?

Hi all,

I notice a beacon on 401.25 MHz that, based on its characteristics, seems to
be part of the DORIS
system<http://www.sirgas.org/fileadmin/docs/GGRF_Wksp/26_Soudarin_et_al_2019<https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.sirgas.org%2Ffileadmin%2Fdocs%2FGGRF_Wksp%2F26_Soudarin_et_al_2019&data=04%7C01%7C%7C1d42825c55524d42bf2208d8f4804e21%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637528179404637084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=qMQN2jD0sbMIrtQUnRcZX3MekKXqfxYZq%2F1zIizMeNg%3D&reserved=0>
_DORIS_and_IDS.pdf> of ground-based beacons that help satellites in orbit
determine their position to very high accuracy. It's sort of a reverse GPS
(ground-to-space). The beacon is a CW tone, with a 0.8 second data burst
every ten seconds, at 1 second before each ten seconds (i.e., 9 seconds, 19
seconds, 29 seconds, etc., past the minute).

I am in Arlington and the closest official DORIS tx site I see listed is at
Goddard. Seems kind of far away for me to be hearing it pretty clearly in
Arlington, especially if it's designed to point up.

Is anyone located near Goddard and could see if there is a signal that fits
this description that's very strong there? Or do other people hear this in
areas that are not near Goddard? I think you'd need a receiver that can do
CW or SSB mode to be able to hear it.

DORIS also transmits on 2036.25 MHz but I can't hear that here, although I
do hear a constant weak CW tone about 10 kHz off that frequency, but no data
burst.

(Apologies if this is too wonky, but I think it's cool finding exotic
signals on the airwaves!)

73,
Andy
W4JE

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