[aprssig] LoRa GPS tracking

Dana Myers k6jq at comcast.net
Mon Aug 8 14:06:16 EDT 2022

Ironically perhaps, I did a test just yesterday with a Part 15 LoRaWAN GPS
tracker on the Helium network. Helium is relatively low-cost to use, I bought
credits for 2,000,000 reports for $20. This experiment definitely gives some
context to the discussion of Part 15 vs Part 97 in a practical way.

My tracker in this case was near the maximum Part 15 power (+30dBm)
with a small mag-mount antenna on my car (no more than +6dBi). I was
running DR0 (SF10BW125) for the sake of testing; further testing will be at
higher data rates that don't offer as much processing gain (and don't
run into the 400mS dwell-time limitation).

I drove from Fairfield, CA to Bodega Bay (Fishetarian lunch, yo). While I
haven't done a detailed analysis, initial mapping shows I was almost
always in coverage except for the very rural section of Sonoma county
between Valley Ford and Bodega Bay (mostly cattle out there).

Map of location pings:

If you're interested in further information, please email me.

Dana  K6JQ

On 8/8/2022 10:50 AM, Scott Howard wrote:
>> Is there a document somewhere that walks through the spread spectrum
>> rules and documents if LoRa counts as SS under Part 97 and if so (or if
>> not) how it meets the rules?  I really have no clue about this and would
>> like to read about it; I do remember somebody getting an STA but they
>> were using a 50W amp and the STA might have been for higher power?
> Here's a talk about the 50W amp with LoRa you mentioned (Dan Fay,
> KG5VBY, at DCC). The link below will bring you right to the part of
> hte talk where he discusses the Part 97 regulations and his STA
> (0721-EX-ST-2018).
> https://youtu.be/AAo2r3mGsBM?t=1024
> Outside of Part 97, this is a summary of the Part 15 rules (for
> completeness): LoRa is typically used as unlicensed ISM (Part 15
> instead of Part 97) which allows for SS emission. LoRa typically is in
> bands around 433 MHz or 900 MHz. In the US, the 900 MHz band (more
> precisely, 902-928 MHz) is an unlicensed band that allows for SS
> emission at higher powers that the unlicensed 433 MHz band, and the
> 900 MHz band also allows for optional frequency hopping SS to achieve
> even higher powers.
> The FCC rules (15.247):
> https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/subject-group-ECFR2f2e5828339709e/section-15.247
> TI has a nice application note (see page 8, "Transmit Power Limits for
> the 902–928 MHz Band")
> https://www.ti.com/lit/an/swra048/swra048.pdf
> Quick summary (for mostly isotropic antennas with gain < 6dBi)
> - If the channel bandwidth is between 25-250 kHz: Power limit
> (delivered to antenna) is +30 dBm. Total dwell time at a specific
> frequency cannot exceed 0.4s in a 20s period (i.e., you have to hop to
> 50 different frequencies within 20s if continuously transmitting)
> - If the channel bandwidth is between 250-500 kHz: Power limit is +24
> dBm. Total dwell time at a specific frequency cannot exceed 0.4 s in a
> 10s period (i.e.,you have to hop to 25 different frequencies within
> 10s if continuously transmitting)
> So you can avoid worrying about frequency hopping by designing the
> system to transmit short messages at low frequency, which fits nicely
> with APRS.
> _____
> Scott Howard, PhD
> Associate Professor
> Department of Electrical Engineering
> College of Engineering Bioengineering Program
> University of Notre Dame
> http://ee.nd.edu
> 574-631-2570 (direct)
> 574-631-4393 (fax)
> https://howardphotonics.nd.edu
> Follow me on Twitter @HowardPhotonics
> 262 Fitzpatrick Hall
> Notre Dame, IN 46556
> _______________________________________________
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