Using RTL-SDR For tracking wildlife radio tags

General
1

Hello All,

Sorry for the longer post but thank you in advance for any help you all may have. I am a student working on my Master’s thesis, which focuses on tracking released juvenile fish fitted with internal hardware external antenna VHF radio transmitters.

One of the biggest challenges with this type of research is accurately documenting fish movement and estimating predation rates. Most wildlife telemetry systems currently used for this work rely on handheld receivers, meaning researchers must be within roughly 50–100 feet of a tagged fish to detect it. This creates large gaps in the data because fish can move long distances between observations or disappear entirely before being relocated.

Commercial autonomous telemetry receivers do exist, but they typically cost between 15k $30,000 per station, making it impractical to deploy enough units for many research projects.

My goal is to develop a low-cost, SDR-based receiver station that I can installed along the riverbank. Rather than following fish with a handheld receiver, these outposts would continuously monitor for VHF radio tags (approximately 148–152 MHz) and automatically log detections whenever a tagged fish passes within range.

I’m new to SDR but have experience with electronics, Arduino, Raspberry Pi, and environmental instrumentation. I’m hoping to learn the best approach to designing a reliable VHF telemetry receiver using SDR technology.

A few questions I have are:

  1. Is an RTL-SDR-based receiver a reasonable starting point for detecting low-power wildlife telemetry tags, or should I be looking at different SDR hardware?

  2. What antenna and RF front-end (LNA, filters, etc.) would you recommend for maximizing sensitivity in the 148–152 MHz range?

  3. Has anyone here worked with wildlife telemetry or similar narrowband VHF applications?

  4. Are there open-source SDR projects that would provide a good starting point for decoding narrowband telemetry transmitters?

I appreciate any advice, recommended reading, or examples of similar projects.

Thank you for your time!

2

I believe that RTL-SDR would be fine for this project, but other higher end choices like an Airspy or SDRplay device would also work well.

To maximize sensitivity I suggest that you find or create a custom bandpass filter for that specific band, and use a QPL9547 based LNA to improve the noise figure. You should place the LNA right by the antenna, and have the cable run to the RTL-SDR after the LNA.

With 148 MHz being close to the broadcast FM band, you could potentially have issues with broadcast band interference. Depending on how bad the interference is, you could place the filter in front of the LNA to protect the LNA from being overloaded by broadcast FM. But doing this will reduce some sensitivity. If FM broadcast band interference is not a problem, put the LNA first to maximize sensitivity.

Also, probably most importantly will be your antenna. You need to use a high gain Yagi or other directional antenna tuned for that band.

3

Thank you for your help. I have never built o ne of these systems is there any general adivce you have before I start?