[amsat-bb] Outernet L-Band Service
n1jez at burlingtontelecom.net
Sat Oct 22 16:12:48 UTC 2016
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!
"A closed mouth gathers no feet"
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