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