EMEA Region L Band Frequencies

Hi,

On https://outernet.is/tech there is a document that shows the current L Band frequency for Alphasat as 1545.525 MHz, however Librarian tunes to 1545.94 MHz when I select the EMEA region tuner preset.

I’ve checked both frequencies using a GQRX and I don’t see much of a signal on either frequency. However when my DIY L Band receiver is running I do get something, but I’ve not seen a SNR over 6dB.

Should I configure a custom tuner profile - or it the existing EMEA preset correct?

Thanks

Update:

I found this: https://github.com/Outernet-Project/Information/wiki/Satellites,-Frequencies,-and-Coverage-Area

That confirms the 1545.94 MHz frequency.

Yes, the wiki on Github has the correct values. There are some inaccuracies in the firmware. That should have been resolved already. Are you using a CHIP or a Pi3?

I’m on the RPi build 2.0a1, which on reflection, appears to be correct. For future changes can the settings/options used in the application be amended with an overlay?

Generally, I’m concerned I’m not getting much more than a few dB SNR with a clear view of the sky and good antenna alignment, using the standard patch antenna and LNA, do you have any suggestions on improving reception. I’m in central UK btw.

Yes, for future changes an overlay should resolve that type of issue.

Are you using the Outernet air gap patch? I’m surprised you are only getting a few dB of SNR. And you are pointed to 25E? Could you take a picture of your set up?

Hi Syed,

I’m using the Outernet air gap patch - all connections appear to be well made and I’m trying to keep the SDR away from the antenna. I have not used any additional co-ax cables so I have:

Antenna + feed line -> LNA -> SDR -> RPi

I’ve attached a picture of my setup. As you can see, I’ve not mounted the components in an enclosure.

The Power LED on the LNA is illuminated.

My location is approx Longitude: -1.24, Latitude: 52.82

It is a clear day and the antenna has an elevation of about 28 degrees and an azimuth of 148 degrees.

I’ve also attached an image showing the very low RSSI and SNR with that current setup and alignment.

FYI - I am now running rxos 2.0a2

Regards

Does your SNR change if you move to a 45-degree elevation?
Would you happen to have GQRX or SDR#? I’d like to see what kind of SNR those applications are reporting. I want to rule everything out before pointing the finger at a radio that has gone a bit deaf.

It’s also possible that you have interference issues locally (harmonics from other signals). A screenshot from SDR# will definitely provide more insight on that.

The following should not matter, but we have noticed that it actually does: Can you rotate the antenna so that the feedline is at the top of the antenna?

Hi Syed,

I have tried different elevations and antenna rotations, the highest SNR I see is 4.3dB.

I’ve attached a GQRX screen shot taken when using the same setup and alignment (Antenna, LNA, SDR). I have the “DC Remove” option enabled to remove the central DC spike, and hardware ACG is enabled. I can see other signals but nothing much at 1545.94MHz.

Hi Jrm,

This is the kind of spectrum plot what you should see. VFO marker is on the actual Outernet signal:

If you have access to a Windows PC give it a try SDR#, as that’s the most reliable SDR program so far (GQRX sometimes quite difficult to set up). Just to confirm the receiver setup is all right.

Zoltan

Hi Zoltan,

I’ve tested with SDR# and I get similar results (see below). I’m not seeing the same clear distinct signals as you have shown in your example. This is with the Tuner AGC disabled and a fixed gain of 14dB. With the RTL and/or Tuner AGC enabled levels are increased in general, but no improved SNR at the tuned frequency. What gain configuration are you using in your example?

I did receive a file today,so the SDR software incuded in ORx is coping with the reduced signal, but it’s not very robust.

Thanks for the SDR# test! From your spectrum plot it looks like the SDR is a bit saturated, that can happen in urban area where strong RF activity happens. You can try to play with the gain settings. There will be a point where increasing gain not helps to increase SNR but the noise floor starts to climb up (a good sign of SDR saturation).

Back to your question I was using 19dB gain setting in SDR#, in a less noise RF environment.

Turning off AGC is advised as it cannot handle the narrow band signals like Outernet signal.

Also finding a good reception position can help a lot for maximizing SNR! The most important that your antenna “see only the satellite” and no other noise sources from the city, if possible. For that reason a wall of a house, or a tree can be a good “natural shield”.

Thanks Zoltan,

Actually I’m in a rural location - I have some typical domestic RF sources (WiFi, DECT phones, Bluetooth etc) - I’ll do a test further away from the house to eliminate potential interference.

Regarding ongoing usage - I’m using the standard ORx image - I notice in the SDR demodulator output that an AFE gain of 45dB is being used - at present I don’t see any options in the Librarian tuner settings to manage the gain - perhaps I should submit a feature request.

I guess this affects the Alpha Lantern as well?

I have not been able to replicate the gain by rotating on an Alpha Lantern, but my colleagues have been able to with a naked antenna. Can you give it a shot and tell us what you find?

Since I only look at fluctuating values (no averages) my guesstimate is that it does not make a difference in my case.

I’ve been receiving Alphasat with > 8dB SNR, RSSI about -98dBm, SER <=0.001 and “CODE LK”, for about 12 hours now, but still show a PER of “-nan” and 0 CRC pass/fails. The constellation plot looks pretty good. This is with the binaries from outernet-linux-lband (v 1.0.4) running on Ubuntu 14.04 x86_64.

Has the channel on this downlink been idling, or is there an issue with the demodulator? Can anyone confirm reception of any traffic through Alphasat recently?

UPDATE:
By the way, I have lots of SDR and conventional radio kit here and usually have hellish problems with intermod caused by high power VHF broadcast and pager transmissions, so I am pleased to see a moderate SER in this system.

Syed told me that all 3 satellites are getting the same files from the carousel.

Send your self a test file on the filecast page.

I seemed to get a lot of files last night.

Syed can we please have a test broadcast list and timetable.

Thanks for the info Seasalt.

The demod and decoder have been running pretty much continuously since I posted yesterday and nothing seems to have come down the pipe from Alphasat at all. I did submit a text file containing a small test message yesterday.

There is an odd bug in the code of our content server/playout system. We should have this resolved by either tomorrow or Tuesday. This issue allows packets to be sent out continuously, but file-content is not being sent. It’s not a problem in the satellite/physical layer. It’s a problem with packetizing the files. We had been receiving files with no issue just a couple weeks ago, so this it’s just a bug that needs to be dealt with.

Sorry about this hiccup.

That’s OK. I’ve been receiving STD-C traffic from Inmarsat 3F2 today instead. It’s working very nicely with the L-band-kit-on-a-bamboo-stick :slight_smile:
Bit of a bummer for you guys though, paying to sent idle tones on the downlink :rage: