How to estimate receiver range

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Thorsten von Eicken

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Sep 3, 2021, 4:28:54 AMSep 3
to Motus Wildlife Tracking System
I'm looking into proposing some stations for Santa Barbara, California and I'm not finding much info about receiver range details. I did see https://motus.org/antennas but some of the questions I have are:

- The https://motus.org/antennas page shows onmidirectional antennas as having a very short range, but there are omnis available with quite high gain (e.g., 7-9dBi). If I plug some numbers into RF range calculators the result is around half the range of a 5-6 element Yagi, not 1/10th as suggested on that page. What am I missing?

- Is there any info on transmitter power for either the Lotek or CTT tags?

- How does one estimate receiver range given topography? I'm very familiar doing that for "normal" radio applications but what I'm missing is transmitter, i.e. bird altitude. I know the answer will be "it depends..." but what's a general assumption if one wants to set-up a string of stations that form a barrier for birds that migrate through the area? I'm also concerned about the effect of using high-rain antennas on birds overflying at higher altitude.

- Has there been any research into low-cost receivers? The CTT dongles contain about $20 worth of hardware that produce a serial text interface IIUC. It seems to me that a low-cost receiver with a simple omni could be built for under $500 including battery and solar. The CTT Terra Kickstarter (https://www.kickstarter.com/projects/theterraproject/listen-to-birds-and-wildlife-build-a-new-conservation-tool) is in a way a proof of that. Is something simple & cheap not really interesting for Motus? (Perhaps because sites are so hard to come by?)

Sorry for the barrage of questions... I'm trying to get into all this and appreciate all responses!

René Janssen

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Sep 13, 2021, 7:38:13 AMSep 13
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Hi!

Sorry that I don't know your name. Indeed a lot of questions that are not simply to answer. 

- Omni's looks great, but pick up also the noise from other sides of the circle of the detection; where yagis had one front loop, a small back loop and maybe two or more small spicky side loops. 

- As you are aware of, I expect, is that the detections of tags has a lot factors. One is noise (and than the noise level is to high to detect further/ nearby tags), Sight of view (buildins/ dunes/ hills/ wet trees/ maise fields/ * ) that stuck the signal etcetera. and height of the receiver as well as fly height. You can install it high above ground level in a light tower for example, but if it has plenty GSM antennas, than you get a lot of noise... So yes, the set-up of your array depends on so much factors! 
Testing the detection range by using racing pigions or bigger bats or bigger birds that you can deploy with a coded tag and a GPS tag would be one of the options to test it in real live. 

- I don't know about low cost receivers. Nooelec are also in use. See the Sensorgnomads group for that. Making it your own sounds cheap; at the end could it be a pain in the *ss and are the costs higher than the positives. Be aware that time cost also money; and organizing good places is most times a hell of a job. 


René 
The Netherlands
Op vrijdag 3 september 2021 om 10:28:54 UTC+2 schreef tvone...@gmail.com:

Denis Lepage

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Sep 20, 2021, 11:51:53 AMSep 20
to Motus Wildlife Tracking System

Hi there,

 

there are no simple answers to these questions. As René points out, range is affected by many variables. Radio-signals work basically with line-of-sight. The higher your antenna, the more range you will likely get, but that may be at the expense of birds located very close to your station unless you have antennas configured to capture that area. In optimal conditions, there has been instances of detections happening 15-25 km away, but I expect those are relatively (very?) rare. Topography, vegetation, and even weather conditions will all have an impact. I would expect that a non-trivial number of detections go unnoticed, or cannot reliably be used.  Someone here did some experiments with racing pigeons double-tagged (Lotek and GPS pinpoints), but this hasn’t been published yet that I am aware.  Many fly-bys within a few km were not picked up by stations, if I recall correctly, but I may be mischaracterizing it. Many other instances have produce nice reliable detections. Fly-bys would have lower chance of detection than foraging or roosting birds that remain for longer in an area. You can try to ground truth your stations and see, but replicating the exact conditions of a tag on a bird that is in perpetual movement in different habitats and positions can be very challenging, to the point where your ground-truthing may not mean very much.

 

I haven’t seen the results from Terra in term of detection range. Without a standard antenna, I would expect it to be significant less than say a Yagi-based station or even an omni. These units are mainly aimed at the “mass“ market where the number of units compensate for the smaller detection range, which can nonetheless help complement the existing array. We’re certainly keen to learn more about whether Terra provides a viable solution under certain conditions.

 

The bulk of the costs of building a station probably remains the infrastructure (antenna, tower, wires). The cheaper reliable option that we can recommend probably remains a SensorGnome as currently suggested. The one area where you may be able to save a bit of money is a cheaper radio dongle, but those have not been really well tested, and we would not recommend them unless you are prepared to do your own evaluations, and if you don’t mind risking degraded data quality (missed detections). I think people who have tried have had mixed experiences.

 

A key challenge in signal processing is teasing out the noise, which may vary immensely depending on your location and the antenna orientation, from the true signal. There are probably useful progress that can be made to apply filtering on the antennas to help reduce noise and enhance true signals, but there is a significant risk that filtering may also remove more of the valid detections, so this is an area where we feel we need to proceed cautiously, and that would require people willing to do sufficient testing under a variety of conditions before we can recommend them. As an NGO, we have no benefit in promoting solutions that are more expensive than they need to be. If we ever find any cheaper and reliable solutions, we will definitely use them for our own arrays to the extent that we can support them, but just finding out takes time and costs money, as pointed out by René. Our efforts are thus aimed at the main products that we know work well.

 

I hope this helps!

 

Cheers

Denis

 

 

Denis Lepage dle...@bsc-eoc.org

Senior Director, Data Science and Technology

Birds Canada

PO Box 160, Port Rowan, ON N0E 1M0

519-586-3531 x155

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The Motus Wildlife Tracking System (Motus) is an international collaborative research network that uses coordinated automated radio telemetry to facilitate research and education on the ecology and conservation of migratory animals. Motus is a program of Birds Canada in partnership with collaborating researchers and organizations. Learn more at https://motus.org
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Thorsten von Eicken

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Oct 1, 2021, 2:47:33 PMOct 1
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Denis, thanks for the thorough response! It sounds like setting up a barrier across a 50-60 mile stretch is not really in the cards without a very significant investment. It seems better to focus on a few hotspots where migrants are known to stop-over and hope that the probabilities work out... The total lack of technical information makes the whole thing even more difficult. (I wish Motus had somehow negotiated that the radio protocols be made public...)

In terms of station cost, the CTT dongles are quite attractive because receivers are very, very cheap. While I do understand that antenna, tower, etc costs dominate, those costs do change if your radio costs <$50, consumes 100mW on average, and has a quarter-wave monopole (or dipole). Suddenly the wind loading goes down a lot, you just need a LiPO or two for a week of power, and a solar panel of a couple Watt suffices. The range will be lesser than a triple-yagi site, but you may be able to place many more?

Is there any documentation of the coding scheme used by the Lotek tags? I've been reading through the source, but that's slow going. I'm gathering each tag sends a pulse burst and the tag ID is encoded in the frequency offset of the pulses and the pulse timing? Is that frequency offset of the radio carrier or is something modulated onto the carrier? I'm asking 'cause I wonder whether one can't use some integrated radio receiver chip, similar to the one used for CTT tags, to receive the Lotek signals. That could also bring the cost and power budget down considerably.

Anyway, I don't mean to imply that the current set-up is no good, to the contrary, it's pretty impressive stuff! I'm just brainstorming in an effort to understand better.

Jim Moore

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Oct 1, 2021, 8:28:14 PMOct 1
to Thorsten von Eicken, Motus Wildlife Tracking System
Thorsten-

To answer your question about coding; the nano tag uses an AM signal too send four 2.5 ms pulses at varying intervals (ms) at variable repetition interval (seconds).  The CTT tags us a completely different modulation system(FSK) which is a serial data stream of 64 bits which gives 2^64 codes.  I have done some extensive tag testing using a drone about 2 years ago.  My conclusion was that the CTT tag significantly outperformed the nano tag in the tests that I ran.  Here is a link to my report if you are interested in the details.

Cheers

-Jim

Jim Moore
Great Marsh Institute
34 Moores Rd
Elverson, PA, 19520

j...@marshlands.org

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The Motus Wildlife Tracking System (Motus) is an international collaborative research network that uses coordinated automated radio telemetry to facilitate research and education on the ecology and conservation of migratory animals. Motus is a program of Birds Canada in partnership with collaborating researchers and organizations. Learn more at https://motus.org
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