[amsat-bb] Outernet L-Band Service

Scott scott23192 at gmail.com
Sat Oct 22 20:09:11 UTC 2016

It is fun, Mike.  If you'd told me a year ago that I would be receiving 
something from geosynchronous orbit, or anything at all above 1GHz, I would 
have asked what you were drinking!

But, thanks to a lot of talented & generous programmers in the amateur 
community, not only can we receive satellite data streams but many of them 
can be decoded.

As for L-band transmissions from Inmarsat 4-F3 (my only point of reference), 
it's become apparent to me that there is considerable variation in both 
bandwidth and signal strength across the spectrum.  As luck would have it, 
the Outernet signal is weaker & more narrow than most of what you see up 
there.  I guess it's safe to assume that you get what you pay for!

Still, it's a completely receivable signal.

I'd like to offer a couple of screen shots that might help you get familiar 
with what to expect.  You can best spot the Outernet signal because there 
are two stronger signals to the right of it.  If you'd like to look at these 
images, you can see what to expect. (Outernet data stream is on the left)




... finally, if you'd like to see a broader view of what is coming down from 
Inmarsat 4-F3, I posted a screen shot from SDRSharp the other day as one of 
several images in a Tweet:


Hope some of that might help!

-Scott,  K4KDR


-----Original Message----- 
From: Mike Seguin
Sent: Saturday, October 22, 2016 12:12 PM
To: amsat-bb at amsat.org
Subject: Re: [amsat-bb] Outernet L-Band Service

I'm interested in the Outernet L-Band service, so today I decided to see
if I could at least detect the signal. I really don't have any optimized
antenna or preamp but I had an idea.

I have an old Trimble 41556 bullet GPS antenna that has a bad output
connector on it. GPS is up around 1575 MHz. Depending on the type of
antenna used, there can be really tight bandpass filtering that won't
pass the ~1539 MHz Outernet signal.

So I opened up the antenna and removed the two bandpass filters in the
unit. Here are two pics of the parts and the simple bypass I did. This
is real meatball surgery <grin>

Here are the filters.

Here is the LNA with red arrows showing where I removed the filters.

The patch antenna used for GPS is designed to look at a large portion of
the sky at once, so I knew the directional gain wouldn't be great, but
what the heck! This is an experiment.

I used my FUNcube Dongle as a receiver. This is one of the original
ones, but it does have a switchable 5v bias tee on the input. I used
this 5 volts to power the GPS antenna.

Just pointing the patch out the window, I see this signal:

So I have something. I assume it's the Outernet signal? It definitely
peaks at the correct AZ/EL for Inmarsat 4-F3 from my location. I do need
to check the frequency calibration of my FUNcube as the signal is higher
than I expected.

The next step will be to use my RTL dongle with appropriate software to
see if I decode anything. I could easily use a better/more directional
(more gain) antenna connected to the GPS LNA by simply disconnecting the

This is fun!


Mike, N1JEZ
"A closed mouth gathers no feet" 

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