21

Cool!

So can I hook this Maverick LNB up to an RFM95W and start decoding?

22

That sub-GHz radio didnā€™t support the 1.6 MHz channel bandwidth. We use the SX1280/81 instead.

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23

Good Choice ā€” from the transceiver data sheet data Semtech SX1280-81 loRa modem

RB_L
LoRa bitrate programmable range with CR = 4/5
SF5, BW = 1625 kHz-202-kb/s
SF6, BW = 1625 kHz-122-kb/s
SF7, BW = 1625 kHz-71-kb/s
SF12, BW = 203 kHz-0.476-kb/s

BW_L
LoRa bandwidth programmable range
203-1625kHz

RFSLP_L
LoRa receiver sensitivity with CR = 4/5 and low power mode enabled 1
SF7, BW = 1625 kHz,ā€“106-dBm
SF12, BW = 203 kHzā€“130-dBm
RFSHS_L
LoRa receiver sensitivity with CR = 4/5 and high sensitivity mode enabled 1
SF7, BW = 1625 kHz,ā€“109-dBm
SF12, BW = 203 kHzā€“132-dBm

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24

Hi Syed,

Poke me on the APAC reseller, teleport and transponder leasing things ā€“ I might have some good solutions for all three for you.

Paul.

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25

Hi Paul: Thanks for the offer. Iā€™ll follow up to your email right now.

26

I will update you soon

27

Does not seem very efficient in a situation where you have to rent bandwidthā€¦ you have to rent the entire width of the chirp and then you get the datarate of the narrow band signal :frowning:
Normally this kind of modulation is used when a wide band is allocated and you want to avoid mutual interference (between users), or when you want to avoid being detected.
LoRa uses it to allow several services to operate in the same band, avoiding interference from and to existing band users that are on fixed frequency.
I donā€™t see why a service that has to rent transponder bandwidth would use this modulation methodā€¦
(as shown above, outernet will have to rent 2 MHz to get 40kbps datarate, while that could be easily obtained with 50-100kHz of rented bandwidth.

28

A 100 kHz DVB-S carrier could not be received by a 2cm antenna.

29

You can get a higher bit rate with a lager dish, or have a much smaller dish with processing gain by seeing the information several times. if you see each bit twice, you get 3dB. If you see each bit 4 times, you get 6dB. So, obviously itā€™s a trade-off. The processing gain is not free. Itā€™s the price you pay for a smaller dish. Itā€™s a compromise.

ā€“Konrad, WA4OSH

30

@Syed
SX-1280 ? I thought this part is for 2.4 GHz. does it run at 1.2 GHz?

11.9024 - 10.750 = 1.1524 GHz
Rx Freq - LO Freq. = IF Freq

Does it run in the 23 cm band (1.240 - 1.300 GHz)?
I did not the freq. range in the spec sheet.

ā€“Konrad, WA4OSH

31

That is the magic of Dreamcatcher.

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32

Got it. ā€¦ secret sauce :wink: :smile:

If the SX-1280 runs in the 23 cm band, there could be an opportunity for a ham alternative to HamWan. 1288.000-1294.000 MHz - Broadband Experimental A potential for 3 non-overlapping LoRa frequencies, a low cost alternative to HamWan

Elon Musk launches loads of satellites to get the needed cash flow to launch a mission to Mars. Just a thought. I will let you concentrate on Outernet.

ā€“Konrad, WA4OSH

33

Is Dreamcatcher 3.01 still in Beta? I hope not. :face_with_raised_eyebrow:

34

Actually, they are in Alpha.

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35

So I now wonā€™t check twice a day to see if youā€™re shipping. Maybe, once a week to see if youā€™ve hit Beta and then RC, And then boxing for shipment.
No problem. :sunglasses:

36

A technical explanation is here starting on page 8. http://www.timedomain.com/wp/wp-content/uploads/2015/11/320-0291C-Part-Two-UWB-Definition-Advantages.pdf they have some good white papers. Not fully overlapping technology but the principals work for narrow band also. You can also use other means to work on reducing the noise.

37

UWB, while a spread spectrum technology, is not closely related to LoRa. But I do see your point. Various technologies such as CDMA, UWB, and LoRa (and even FM) have processing gain because the same information is being sent several times. The processing gain is the ratio of the total information sent to the actual information sent. In spread-spectrum technologies, this is the spread bandwidth divided by the baseband bandwidth, or the spreading factor. The point is, if you send the same information twice use it to increase your receive sensitivity by 3dB. If the spread factor is 4, you get 6dB, etc. A spread factor of 100 gives you the equivalent of 20dB of receive sensitivity.

LoRa has processing gain due to its spreading factor.
LoRa Spreading Factor & Data Rate

ā€“Konrad, WA4OSH

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38

Agreed. And understand this is not uwb. If you are buying a big chunk of bandwidth, itā€™s possible to send multiple signals spread spectrum with repetition within the bandwidth to get snr and bitrate boosts. Iā€™m not sure which would work better for this application as cost is a major factor.

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39

Hopefully there are ways that chirps can be sent orthagonal to each other. Orthagonal chirps could be combined and sent in the same frequency bandwidth. I just donā€™t have a clue as to how many that would be. Of course, I have not looked into it either. :wink:

Incidentally, I worked on IS-661, an attempt to replace the TDMA phy layer with a new PHY that would get processing gain and better frequency re-use. It used spread-spectrum techniques and had the same upper layers as GSM. The idea was to try to get the best of CDMA - good processing gain, but spectrally inefficient and combine it with GSM - spectrally efficient, but no processing gain. The hope was to get good frequency re-use and some processing gain. The result - the worst of both technologies.

This is why PCS went with GSM instead of IS-661. But, it got us the pioneer preference license for New York City, worth far more than our R&D efforts at Omnipoint.

ā€”Konrad, WA4OSH

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40

@Garyalexander
Interested in the idea of more efficient LoRa spectrum, Iā€™m interested in the topic of Orthagonal and Quasi-Orthagonal CSS (Chirp Spread Spectrum). I have not started reading these papers. It would make an interesting survey paper for some Masters student in the field of Satellite Communications.

Quasi-Orthogonal Chirp Signals Design for Multi-User CSS System

Xing Ouyang and Jian Zhao, Orthogonal Chirp Division Multiplexing unpublished?

Iā€™m also interested in inter-symbol interference, the foundation for the above papers.
Taeung Yoon, Dahae Chong, Sangho Ahn, and Seokho Yoon, Bit-Error-Rate Performance Analysis of an Overlap-based CSS System World Academy of Science, Engineering and Technology International Journal of Electronics and Communication Engineering Vol:3, No:2, 2009

ā€“Konrad, WA4OSH

1 Like