Learning to use SDRplay for Inmarsat

Post your feedback here
jon
Posts: 291
Joined: Tue Jan 06, 2015 10:48 am

Learning to use SDRplay for Inmarsat

Postby jon » Sat Jan 09, 2016 9:25 am

K4KDR posted this on the Facebook Group site https://www.facebook.com/groups/sdrplay/

I learned a couple of lessons this week with my SDRPlay that I thought might be worth sharing. This might be a lot longer than most of the posts here; I hope that's ok. Very sorry if I'm out of line.
Summary: L-Band Inmarsat / poor initial results from home-made patch antenna / better results after some changes
Note that keeping costs to near zero was a priority.
There were several reasons that I upgraded from a generic RTL-SDR to the SDRPlay & one of them was certainly the ability to explore the higher frequencies with more bandwidth and greater sensitivity. Turns out that receiving a signal from a geosynchronous satellite some 23,000 miles (~37,000 km) up is a little more tricky than decoding CW on the 40 meter band!
So after searching the web and reading everything that I could find from all the wonderful people who have shared knowledge on the subject, I decided that I needed to build an antenna. Since I have had such great success with the QFH antenna that I built for 137MHz weather satellites, I used an online calculator (http://jcoppens.com/ant/qfh/calc.en.php) to build a tiny little QFH for the 1.5GHz band. Imagine my surprise when I actually saw signals! They were too weak to decode but it was just cool seeing data streams from so high up (both in frequency and altitude).
About the same time I started seeing references to a "patch" antenna that was supposed to have some directional gain. I found this YouTube video particularly interesting:
https://www.youtube.com/watch?v=OY0hvWsH-mg
... so of course I HAD to have one. The video provided the dimensions but not quite all of the construction detail that I needed. I found a very helpful page that gave more detail:
http://www.rc-cam.com/gp_patch.htm
... after shopping for materials and ordering a suitable SMA connector online (http://www.amazon.com/gp/product/B005T9OY04), I put together an L-Band patch antenna as precisely as I possibly could. It was a very fun build and I was super pleased with the finished product.
Convinced that I was going to immediately receive every signal from every satellite in the entire world, I searched online to find out the compass direction to the nearest Inmarsat satellite. I went to the appropriate window in my house, connected the nice new patch antenna, and started tuning up through the 1.5GHz band. And... nothing. Well, not "nothing", but no signals stronger than I saw on the QFH and certainly nothing strong enough to decode. But hey, it was a GOOD-LOOKING antenna!
So it must be my location, right? First chance, I drove to an area with open sky and tried again. The signals were a LITTLE bit stronger and if I held my mouth just right, I could actually decode one or two of the "aero" channels up around 1.545. Being on a budget, I took that as a victory!
Since then I have been thinking about getting an LNA as well as maybe building a higher gain antenna. But the other night, I was once again exploring the L-Band and the results were the same. Then something strange happened... as I was moving the antenna around, my signal jumped. I started slowly moving the patch antenna around the window over the kitchen sink (south) and after a lot of trial and error, found a dramatically higher signal on those 1.545 aero channels in one exact position. My decode rate went WAY up but the signal was still borderline and often faded below the level required for usable data.
Lesson #1: Never assume that one antenna behaves like all the others. Apparently things are quite different with THIS type of antenna and/or at these higher frequencies. (both of which were new to me)
So, short of buying an LNA or building a bigger antenna, was there anything else that I could do to improve my signal? I was using a decent SMA-SMA cable but was there room for improvement? In anticipation of maybe having an LNA one day, I ordered a couple of higher quality 30cm MPD Digital SMA-SMA cables on Amazon. (http://www.amazon.com/gp/product/B00AMZTI6U) Those arrived today so I got everything setup over the kitchen sink again. I'm sure that you can see Lesson #2 coming... my signal jumped again - significantly!
It's so tempting to use whatever cables you have laying around, but on this project I got a reminder: Not all cables are created equally. Lesson learned.
I still don't quite have enough signal to decode misc. Inmarsat-C channels but I sure do see a lot more of them now. And as for my happy aero place up at 1.545... well, I'm all over those channels now and pretty happy about it. I'm locked solid with 4 nice dots on the constellation view and a nice stream of messages being decoded.
Below are a couple of screen shots if anyone has not seen what you find up there:
(1200bps on the wider data stream and 600bps on the narrow stream)

Image

So if you have read this far, I hope you might have found something helpful, interesting, or both. What I really wanted to do with this was pay back a little bit to all the people who have posted articles and videos online for me to learn from.
73 everybody!
-Scott, K4KDR
Montpelier, VA USA
Last edited by jon on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Learning to use SDRplay for Inmarsat

Postby g1hbe » Sat Jan 09, 2016 10:56 am

Scott, I've had similar experiences. I started with an active patch antenna and later moved to a home-made yagi with the patch as the driven element which worked great, but I noticed that the signals were always several dB stronger if I beamed through the brick wall instead of the window. I then remembered that the windows in this house are double-glazed with Pilkington-K glass, which has a metallic coating to help keep the heat in. Doh! :roll:
Last edited by g1hbe on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason
Andy

User avatar
IW2NYX
Posts: 9
Joined: Thu Dec 31, 2015 7:49 pm

Re: Learning to use SDRplay for Inmarsat

Postby IW2NYX » Sat Jan 09, 2016 2:22 pm

g1hbe wrote: but I noticed that the signals were always several dB stronger if I beamed through the brick wall instead of the window.


For sure your is not a reinforced concrete house, otherwise you should get ZERO signal.

Are the walls made by brick & mortar or is wooden construction ?

How may dB you gain pointing your antenna outside, without any material obstacle ?
Last edited by IW2NYX on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Learning to use SDRplay for Inmarsat

Postby g1hbe » Sat Jan 09, 2016 4:24 pm

Hi. Yup, bricks and mortar, over 100 years old and still standing. I tried the setup outside to see if the signals got any stronger, but from ground level (my radio shack is upstairs) the path is obstructed by more bricks and mortar (that's next door's house!).
Last edited by g1hbe on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason
Andy

User avatar
IW2NYX
Posts: 9
Joined: Thu Dec 31, 2015 7:49 pm

Re: Learning to use SDRplay for Inmarsat

Postby IW2NYX » Sun Jan 10, 2016 2:16 am

That's good, so you have a big margin in your link budget, i wonder which signal level would catch your L-Band antenna without obstacles.

Could you post a photo ?

Have you conducted any Aero channels decoding with Jaero ?

If positive, what ENOB's values you saw ?
Last edited by IW2NYX on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Learning to use SDRplay for Inmarsat

Postby g1hbe » Sun Jan 10, 2016 11:09 am

So far I haven't even attempted any decoding, as my time is at a premium atm. I'm currently trying to rescue a water-logged loop antenna so I can get back on 160m.
Last edited by g1hbe on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason
Andy

CaptainNemo
Posts: 114
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: Learning to use SDRplay for Inmarsat

Postby CaptainNemo » Mon Jan 18, 2016 8:50 am

jon wrote:... I searched online to find out the compass direction to the nearest Inmarsat satellite...

Anyone can suggest a good site to find inmarsat azimuth/elevation given my lat/lng?
tnx
Last edited by CaptainNemo on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

K4KDR
Posts: 10
Joined: Tue Jan 19, 2016 3:26 am

Re: Learning to use SDRplay for Inmarsat

Postby K4KDR » Tue Jan 19, 2016 3:30 am

This is the one that I've been using:

http://www.groundcontrol.com/Satellite_Look_Angle_Calculator.htm

-Scott
Last edited by K4KDR on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

0815
Posts: 45
Joined: Sat Jan 30, 2016 3:07 pm

Re: Learning to use SDRplay for Inmarsat

Postby 0815 » Sat Jan 30, 2016 6:09 pm

Hi Gents,

Well i am also getting some signals from Inmarsat - very low but enough for decoding some frames:

tried SDRplay + SDR# with LNA4all, Logperantenna mounted on a 60cm offset dish:

http://jontio.zapto.org/hda1/jaero.html
Got good data @ 600 and 1200 but no data @ the 10.5k channels as they are to low SNR here

http://www.inmarsatdecoder.com
works good on low low SNR - demo only - and shows virus on firefox and avira - flase positive??? - does anybody know if it is worth buying the full version??

http://www.tekmanoid.com/egc.shtml
works but only on good SNR....

also wanted to try the iridium - but i have much to low signal to get anything......

maybe some user can share their experiences too... - thx

regards
0815
Last edited by 0815 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

andyj
Posts: 2
Joined: Mon Jan 18, 2016 9:16 am
Location: Central UK

Re: Learning to use SDRplay for Inmarsat

Postby andyj » Thu Feb 04, 2016 5:38 pm

Hi.
I recently started investigating satellite reception on L band.
Setup is a 60cm TV dish with a home made LHCP helical antenna and minikits preamp as described here.

http://www.uhf-satcom.com/lband/

Software is SDR# and JAERO but at the moment I'm only using an RTL-SDR 820T2 stick.
It all seems to be decoding well but is just about on the limit with the 10500 bps signals. ( 4-5db signal strength, which shows how good the software is! )

My question is, how does the SDRplay compare to the RTL stick at these frequencies. Has anyone used both and is there much difference ?
I'm pretty sure there must be but I don't have an SDRplay yet to compare.
Thanks
Andy

Image
Last edited by andyj on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason


Return to “New Users' experiences”

Who is online

Users browsing this forum: No registered users and 1 guest