[amsat-bb] Outernet L-Band Service

[Mike Seguin]

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
-- 

73,
Mike, N1JEZ
"A closed mouth gathers no feet"