[amsat-bb] Outernet L-Band Service

Mike Seguin n1jez at burlingtontelecom.net
Sat Oct 22 21:02:22 UTC 2016

Hi Scott,

Tnx for the images. Big help! So I am seeing Inmarsat, but I need more 
gain. Time to dig out a WA5VJB log periodic and AD6IW preamp I have here 
and see what that does.


On 10/22/2016 4:09 PM, Scott wrote:
> 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)
> http://k4kdr.github.io/files/outernet/2016-10-06--Outernet-HDSDR.png
> -and-
> http://k4kdr.github.io/files/outernet/2016-10-14--Outernet-GQRX.png
> ... 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:
> https://twitter.com/scott23192/status/786804580625428482
> 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.
> https://www.dropbox.com/s/t9r9pwitjzjjgxq/filters.jpg?dl=0
> Here is the LNA with red arrows showing where I removed the filters.
> https://www.dropbox.com/s/3w6q78kocvzvw3m/Trimble.jpg?dl=0
> 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:
> https://www.dropbox.com/s/48fhr38vwhylozz/Outernet.JPG?dl=0
> 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
> patch.
> This is fun!
> Mike


Mike, N1JEZ
"A closed mouth gathers no feet"

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