[amsat-bb] Outernet L-Band Service

[Dani EA4GPZ]

El 19/10/16 a las 18:03, Rick Walter escribió:
> Since reading about the Outernet, I am becoming more curious. I have
> a Funcube Dongle Pro + connected to my discone antenna going into my
> windows 7 laptop, running SDR Console. I am hearing a signal that
> sounds like data with about 2-3 second breaks every so often. The
> frequency is 1,539.793 MHz and I have the decode in Data USB 24 KHz
> bandwidth. The signal is -60 dBM on the signal strength meter. Is it
> possible I am hearing this signal from the bird or could it be a
> local source? I already have 4 versions of the Raspberry Pi but
> figured this would be a reason to purchase the version 3! We all need
> a good excuse to present to the XYL.

Hi Rick,

The signal you describe doesn't seem to me like Outernet's signal.
Outernet's signal is a bit more than 4kHz wide and it doesn't have any
breaks in it.

-60dBm on your SDR software doesn't really mean anything unless you have
calibrated your signal meter (and -60dBm would be way too high for
Outernet's signal). What is strength of the noise floor?

Some 10's of kHz above Outernet you have 2 other signals from the same
Inmarsat satellite. They are a bit narrower than Outernet and much more
stronger (perhaps 10dB even). I would use those to check if you hear the
bird.

I haven't run the numbers, but I wouldn't expect that you'll be able to
hear Outernet with a discone and no LNA. In my experience the FUNcube
Dongle Pro+ is not very good at 1.5GHz (but I haven't done any serious
tests), and if you have a long cable run from the antenna to the dongle,
then you definitely need an LNA.

By the way, Outernet's software doesn't support the FUNcube dongle, only
the RTL-SDR or MiriSDR. You may want to look at
https://github.com/daniestevez/gr-outernet
which supports any SDR that works in GNUradio.

> Finally, I keep thinking if I get all the components to grab this
> data, is it really worth it other than to say I did it? Thanks for
> any guidance or comments. Rick - WB3CSY

That's something you'll have to decide for yourself. What you currently
get is:

* An hourly small file with a listing of all APRS packets sent through
satellites or the ISS and all APRS packets containing the word OUTNET.
* Some grib files with the weather (most useful to sailors)
* Some other weather data
* Random (most popular) wikipedia pages

Most of the bandwidth is spent with wikipedia pages, and the bandwidth
is not so high: you can only get about 15MB worth of files per day.

Of course you could get the same content on the internet.

If you just want to see how it looks like, I have several brief SDR
recordings and recordings of Outernet frames that can be used with
https://github.com/daniestevez/free-outernet/

One reason to get the hardware for Outernet (LNA and perhaps patch
antenna) is that it can be used used not only to receive Outernet but
many other things on the L-band.


73,

Dani EA4GPZ.