Modifying Outernet antenna for dual polarization?

If I wanted to add a LHCP connection on my Outernet antenna as well, would I just attach another feedline on one of the sides adjacent to the existing feedline?

For Thuraya reception? @zoltan is better suited to answer this question.

I want to use it as a feed for a dish pointed at GOES-16, which has a dual-circular-polarized downlink.

Did you want to use two antennas at the same time?

No, that’s why I wanted to see if I could add a LHCP feed to the patch, so I could have both RHCP and LHCP coming off of it.

Hi,

Probably you are looking for Lucas Teske’s Open Satellite Project? That’s pretty cool! I was following the GOES-16 mission, not sure if they still fine tuning it and the image is just relayed from an other sat or it’s fully operational now?
http://www.rtl-sdr.com/tag/goes16/

I guess you need to drill a new hole for the LHCP feedpoint (the very same distance from the center of the patch element, just rotated) For some hints check out Adam’s explanation: http://www.rtl-sdr.com/building-and-testing-an-l-band-patch-antenna-for-inmarsat-c-reception/
The hardest part is to make the aluminum back plate solder able… you will need brass rivets.

I want to use it as a feed for a dish pointed at GOES-16, which has a dual-circular-polarized downlink.

As my best knowledge GOES-16 doesn’t use circular polarization, it uses linear polarization. Where did you get this info?

Update: hmm you are right: GRB is dual CP, that is RHCP and LHCP (each polarity having a different data link)
but HRIT is much simplier, it is just linear

what is your target SDR to decode GOES-16?

sounds like you will need 2 independent receivers for RHCP and LHCP

I’ll be using a TBS 6903 DVB-S/S2 dual-tuner PCIe receiver, it supports the generic stream encapsulation used by the GRB downlink. I’ll be playing with HRIT as well using a grid antenna with a modified feed, and probably one of my Airspy Mini units.
Thanks for the tip on the brass rivet!

Thanks!

You can try modifying the stock Outernet antenna using brass rivets, however note that the plastic screws will break off…they forced by some strong glue so hard / impossible to open without break. You can get those plastic screws from ebay for example.

If you already disassemble the antenna might it easier to replace the aluminum back plate with a brass plate which can easily soldered for the coax GND skirt.

GOES-16 Frequencies are up around 1680MHz and above, which is substantially higher than the Outernet patch seems to be optimized for. Not saying it won’t receive at all, just saying it will not be particularly great compared to a properly fitted antenna. Why not just build a simple 3 turn helix on a piece of copper plate?

I tested GOES-13 (same frequency range as GOES-16) with outernet. It does work fine if you have a big enough dish (like a do), but its easy to do a Linear feed or Single CP feed (like a helix) that I think it doesn’t worth it.

Also the GRB has two independent channels, although its good to receive both, you dont need to necessarily. They transmit different data but they’re complete independent.

So far I would not recommend trying an SDR System with GRB (at least one that you will do the demod in your PC), since the GRB Rate is very high (about 15Mbps per channel). Since they use DVB-S2, its best to get a DVB-S2 commercial receiver that can support any type of stream and use it. It costs about the same price of an SDR and might even have two channels.

I’m in the process to build a GRB station to make the tests and see whats the minimum usable system (NOAA recommends 4.5m dish for GRB!) and see which hardware can be used. There are some (few) other people that is build as well. You’re welcome to join to test it :smiley:
Sadly usa-satcom (on twitter) tried with a 1.8m dish, and even with a perfect system and weather, it was not enough to have demodulated data (although it was pretty close, about 1 or 2 dB off on SNR)

EDIT: Just saw you’re planning to use with the TBS, thats the way to go. Although usa-satcom did a test and it can’t even find the signal with a TBS, then dr.mpeg on twitter did run with the same IQ with a higher grade hardware (Ayecka) and got almost locked.

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Is there a list of what products are on each of the two channels? I’ve not been able to find that yet on any of the GRB spec sheets.
Though I hadn’t noticed the dish size requirements. That sounds like a non-starter for me, at least at my current location :frowning: I guess I’ll stick to HRIT.

As an alternative to modifying the Outernet patch, are there any other antenna designs that work for dual circular polarization? Ku-band c-pol LNBs do some waveguide trickery to feed the two circular polarizations to separate antenna elements, but I don’t know enough RF waveguide magic to understand it :slight_smile:

Yes there is. Actually GRB is one of the most well specified telemetry protocols:

Page 26 of the file or page 4 of the document. It lists the products per channel.

Yes, there is a Septum Feed (its actually what’s used for that type of reception) that outputs both RHCP and LHCP.
HAM’s use for EME (one port to TX and one for RX) because it has a very high isolation between ports. High enough that you can pump out 200W on one port and have your SDR in the other port without burning it.

I did a adaptation of a existing Septum Feed calculator here: http://www.teske.net.br/lucas/septum (the credits for the original formulas and spreadsheet is on the page). I’m building one myself, but my dishes will only be available by august or october.

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Nice, thanks for both!