help needed: RPi3 SDR receiver for wildlife radio telemetry
William Oakley
Hi All,
Using Gqrx, a Raspberry Pi 3B, and other relevant parts, I have managed to build and test a very simple prototype of a portable, low-cost, open-source Raspberry Pi-based SDR receiver to use in wildlife radio telemetry (i.e. detecting/tracking animals attached with VHF transmitters to study their movements and behavior). Unfortunately, I’ve run into a problem that I’m hoping that you all can help me understand and solve. (Note: I am a biologist/ornithologist new to SDR and Gqrx and with limited experience in programming outside of R.)
Brief overview of the issue: While field testing my prototype receiver outdoors, I was not able to detect my VHF radio transmitters at a distance greater than ~40 feet (~12.2 meters). Within ~40 feet of the transmitter (whether indoors or outdoors), I am able to hear the beeping of my radio tags through my headphones and I can also see the tag pulses in Gqrx’s spectrum frame waterfall and audio frame.
(see attached images and text below for more background info and detail on my receiver setup)
Questions:
1) Why might I only be able to detect the VHF radio tags at short distances?
2) Is the issue with my signal-detection a hardware or a software problem? Or maybe both?
3) Are there options/settings within Gqrx (besides ‘audio gain’) that can help increase my tag detection distance?
4) Given the equipment and software I’m using, is it even possible to make the kind of portable SDR receiver I want that can detect VHF radio telemetry tags from 500 meters up to several kilometers away?
Any insight, tips, or recommendations you could provide would be greatly appreciated. I'm happy to provide, upon request, any additional info that I didn't include here.
I've had a lot of fun over the last two months teaching myself about SDR, Gqrx, etc. and trying to build this low-cost, open-source receiver.
Thank you all for your time and consideration and for your dedication to Gqrx, SDR, and open-source projects.
Respectfully,
William Oakley
PhD Biology candidate
Eli Bridge Lab
University of Oklahoma
Norman, OK, USA
http://thebridgelab.oucreate.com/
Background: I am a biology graduate student trying to make a low-cost, open-source, Raspberry Pi-based VHF SDR receiver that I (and any other biologists, ecologists, etc.) can use in the field to radio-track and monitor terrestrial animals carrying VHF radio transmitters (see attached images and links). Ideally, the open-source, cost-effective SDR receiver will be designed so that a biologist with limited skills and knowledge in electrical engineering/computer-science would be able to assemble, program, and use it effectively. And just as important, the SDR receiver will operate just as effectively, and with similar or greater features, than the expensive and limited number of wildlife telemetry radio receivers currently available.
Things I’ve tried so far to troubleshoot the problem:
My non-SDR receiver (Telonics TR-4) is able to detect the radio tag from much greater distances than 40 feet, so I know the issue is not with the radio tag.
I tried changing my SDR tuner dongle, but that did not improve detectability. (The first dongle was the RTL-SDR RTL2832U V3; the second dongle was the FUNcube Dongle Pro+).
Increasing the gain inside Gqrx’s Audio Frame did not help much at all.
Receiver and Antenna System Setup:
Hardware: Raspberry Pi 3B; RTL-SDR RTL2832U V3 tuner dongle; Wave Share 5-inch HDMI LCD touchscreen; 3-element folding Yagi-Uda antenna (tuned to 150.00-151.00 MHz); 3-foot coaxial cable; Bose headphones
Transmitters: I have three radio tags that transmit at 150.949 MHz, 150.528 MHz, 151.016 MHz, respectively. Each tag weighs less than 1g and is designed for radio-tracking small songbirds.
Software: Gqrx SDR (version 2.11.4 for Raspberry Pi 3); Raspbian Stretch Lite (two versions: release date 2018-03-13 & release date 2018-04-18); drivers for the LCD touchscreen; regular updates and upgrades of Raspbian software/system packages through terminal commands)
Image Descriptions:
IMG_0736 – indoor-testing of SDR receiver system using all three radio transmitters and an omni-directional whip antenna; me holding one of the transmitters; (touchscreen not used here)
IMG_0633 – indoor test: Rpi3B with touchscreen attached and Gqrx operating (a different radio transmitter device was used for this test)
Link: wildlife radio telemetry http://www.migratoryconnectivityproject.org/vhf-radios/
Robin Gape
William,
the most likely issue for the symptoms that you describe is that the RF gain requires adjustment. That is found on the Input co… tab. For the RTL dongles, the simplest solution is to select the Hardware AGC check box. For the FCDPP there are gain sliders whose default is probably too low. The only option is manual adjustment, even though the automatic check box appears to be selectable—it will have no effect with an FCDPP.
Note that excessive gain settings will overload the system, especially in an environment with a lot of RF, such as a city, near a broadcast or paging station, or too close to a mobile network cell site.
HTH, Good Luck,
Robin, G8DQX
PS: It may be some other problem, but RF gain is a good place to
start.
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William Oakley
Simon Kennedy
Robin,Thanks for the reply.I have tried checking the Hardware AGC check box and also adjusting the RF gain as you suggested but with no luck. (I had been aware of this option after reading your reply to an earlier, similar post in this group.) But I'll keep messing around with the gain settings and other options and perhaps even try different dongles.The FCDPP doesn't give me a clear signal like the cheaper RTL dongle I've been using.I'll see if there are any other similar SDR/radio tech Google groups or online forums that might be better suited for my problem, as I recognize that my issue does not deal entirely with Gqrx (which is the focus of this group). But I do hope that I can continue using Gqrx for my project.Thanks again for your help. I'll be sure to keep you (and this group) abreast of any developments and/or breakthroughs I have with my project.
