Ideas for RF tracking at range of 3-20m - Page 1
Forum section: electronics / projects

author: RicDG
author_rank: Newbie
timestamp: July 05, 2025, 05:07:43 am
content: I'm trying to design a helmet mounted camera tracker which will follow a target (such as fellow cyclist or skier) at a range of 5-20m, and I'm hoping that someone might have an idea to solve this challenge.My first attempt was to use the signal strength from one or more directional patch antennae, but I never managed to get useful data for directional tracking.My second attempt was based on computer vision using OpenCV's MOSSE algorithm running on a R Pi3A+. Although it tracked at 100fps, it was unreliable and impractical to re-identify the target in the field.My third attempt was using a pair of Ublox's ZED F9P RTK GPS modules; one worn by the target, transmitting co-ordinates to the cameraman's GPS receiver in RELPOSNED mode, which gave the relative bearing to a R Pi to control the camera's servo motors. Once again, this setup worked intermittently in the field, but due to RTK's onerous signal requirements I could not maintain a consistent GPS signal lock for reliable operation in my challenging environment.My fourth idea was to use a pair of UWB modules on the camera's helmet which would provide the relative distances to a UWB module on the target. Much like my attempt at directional antenna tracking, the distance measurements were not sufficiently reliable in this environment, mainly due to the two anchor modules needing to be mounted close to each other.I have researched Bluetooth angle of arrival tracking, but it seems that this technology has not advanced to be sufficiently robust and user friendly.I'd appreciate any other ideas (particularly for RF tracking) that might be more effective for my helmet mounted application.Thanks

author: Andy Chee
author_rank: Super Contributor
timestamp: July 05, 2025, 06:40:37 am
content: Quote from: RicDG on July 05, 2025, 05:07:43 amUWB is the goto technique for this. It is used in smart suitcases that follow the passenger.Your range of 3-20 metres also could implement ultrasonic ranging.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: July 05, 2025, 03:42:36 pm
content: Some time ago I successfully tracked one 24GHz radar position using another one. Tracker radar was 2d monopulse, and the active tag was single antenna with radar chip transmitting at close frequency. Of course, low pass filter cutoff was much higher than for ordinary Doppler applications. I used radar chip prescaler output to set the same "channel". Difference in radar frequencies should be within ADC sampling capabilities. By taking FFT from each antenna and comparing phase at difference frequency angles to active radar tag can be extracted. Theoretically it can be applied here, especially at lower frequency bands where decent low cost parts are not rare.

author: Skashkash
author_rank: Regular Contributor
timestamp: July 05, 2025, 04:06:06 pm
content: Just tossing ideas out here.Any chance to use lidar and retroreflector on the target?Or possibly an active IR transponder.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: July 06, 2025, 11:51:15 am
content: These are all good ideas. I think there might be a problem with active IR/RF tag visibility. So, multiple IR modulated tags or lower RF frequencies to reduce occlusion effects.

author: David Hess
author_rank: Super Contributor
timestamp: July 06, 2025, 01:49:51 pm
content: Quote from: RicDG on July 05, 2025, 05:07:43 amAssuming symmetrical antenna directivity patterns, phase should work much better than amplitude. I made several handheld direction finders which worked very well using phase at close range.Quote from: RicDG on July 05, 2025, 05:07:43 amI think vision is the way to go since it will only get easier and better as computer performance increases. Could the target wear something distinctive making identification easier, like a colored patch?

author: RicDG
author_rank: Newbie
timestamp: July 07, 2025, 03:23:21 am
content: Thanks guys, for those ideas. I am new to this forum and a beginner in electronics.I believe that most of my prior attempts would have succeeded in a more controlled environment, i.e. not mounted on a moving helmet, nevertheless I am keen to find a solution.Andy, I have tried the UWB approach with Makerfabs ESP32 modules, but I wasn't able to reliably track given the precision needed when the anchors are mounted only 18cm apart on a helmet. I may have another go at this if nothing else works. Those suitcases are smarter than me!Shashkash, I need to investigate whether it would be practical to mount a Lidar on a helmet as well as a camera. It seems an expensive option and will need an omni-directional retroreflector. Thanks for that idea.Gregory, yes, I did consider IR, but my research appears to indicate that IR detection would not be effective over 20m in sunny conditions, even if it were pulsed. This is due to my conditions, i.e. the target's orientation is changing relative to the camera so the IR emitter would need to be omnidirectional and fairly compact, meaning an IR emitter panel array is not an option. I'm interested in any further details/links you are able to provide regarding your experience with antenna phase tracking, as this technology is probably beyond my expertise. I had decided that trying to configure Ublox's XPLR-AOA-3 kit was beyond me, and its size was a bit too big to fit on a helmet.David, for my application, my experience with computer vision in this environment is that the OpenCV and YOLO trackers are quite effective but not perfect due to the challenging environment, with occlusion and rapid movement of both the target and the helmet carrying the tracking camera. So it works very accurately for a few seconds until one goes over a bump or the person wearing the tracking helmet makes a significant head movement. I am experimenting with a way to self-restore a CV tracking failure using YOLO detection when tracking fails, but this possible whilst the target is still within the camera's field of view. A more robust method to restore CV tracking would be to use a non-CV tracking method such as RF detection.

author: Swainster
author_rank: Frequent Contributor
timestamp: July 07, 2025, 05:29:32 am
content: Search for UWB 3D angle of arrival. I saw a pretty good demo of this using a Murata eval/dev board. With this technology there only needs to be 2 participants (i.e. you and your target), no need for extra anchors.