GPS over Fiber / GPSoF solution - Page 1
Forum section: electronics / projects

author: Smile2016
author_rank: Regular Contributor
timestamp: February 18, 2025, 08:31:49 pm
content: I'm planning to build a GPS over Fiber (GPSoF) module pair TX/RX to distribute a GPS timing signal from my attic throughout the house. Since existing solutions are unaffordable for amateurs, I'm exploring ways to repurpose lower-cost modules available on the market. My initial idea is to re-use HDMI over optical or SFP transceiver's electro-optic modulator (EOM) and optical-to-fiber components. . I'm aware it is complex so any suggestions from experts would be greatly appreciated anything such ideas, wavelengths, bandwidth, modulation, signal conditioning, gain controls etc...

author: aeg
author_rank: Regular Contributor
timestamp: February 18, 2025, 11:49:52 pm
content: Do you want to distribute time, frequency, or both?

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 04:30:37 am
content: Quote from: aeg on February 18, 2025, 11:49:52 pmbasically this :https://rfoptic.com/introducing-rfoptics-programmable-gps-over-fiber-gpsof-solutions/convert RF signals to optical signals and back

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 03:31:12 pm
content: Quote from: edavid on February 19, 2025, 02:53:17 pmI want a replica of the RF signal from the antenna, transmitted through an optical medium to the GPS receiver at various locations in the house. I'm interested in the timing aspect only. I don't want coax.

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 04:59:31 pm
content: Quote from: edavid on February 19, 2025, 03:39:31 pm

author: fourfathom
author_rank: Super Contributor
timestamp: February 19, 2025, 05:24:13 pm
content: I've got nothing against fiber optics, but the coax loss can be handled by a low-noise amplifier at the distribution point. Multi-output amplified GPS RF splitters are available for a fairly low cost (seehttps://tapr.org/product/gus-gnss-antenna-splitter/for an example). Optical splitters are more expensive. The delay over optical fiber is only slightly less than that of coax cable (so timing and position accuracy may still require compensation), and reflections on properly-terminated coax are not really a problem.

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 05:50:08 pm
content: Quote from: fourfathom on February 19, 2025, 05:24:13 pmI currently have similar DIY setup with 25dB LNAs + splitters . I just want to improve...

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 07:57:38 pm
content: Quote from: edavid on February 19, 2025, 07:18:30 pm

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2025, 08:14:10 pm
content: Quote from: Smile2016 on February 19, 2025, 07:57:38 pmYou have misquoted edavid and others.I suggest you learn how to quote previous messages and interleave your response. It isn't difficult, but is a pain on a "consumption device" such as a phone or tablet.

author: Smile2016
author_rank: Regular Contributor
timestamp: February 19, 2025, 09:46:58 pm
content: I'm always learning, so I apologize for any misquotes, David.In the meantime, I'm examining an optical HDMI TX/RX cable. Unfortunately, there's no easy direct physical access to the laser diodes as they are die wire-bonded. Therefore, I think it would be best to start with a simpler optical sub-assembly, including a diode and detector. OPV314 Series Datasheet as example:https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OPV314-Series.pdfOnce again, I'm focused on finding a feasible optical solution at a lower cost, rather than exploring alternative options.

author: Perrold
author_rank: Contributor
timestamp: February 20, 2025, 06:54:42 am
content: This is something that I have attempted on and off over the years. It works and it's far less intimidating than at first glance. The SFP transceivers are a good starting point as the LD and PD tends to be much more easily accessible. Single mode fiber is your friend here. Biasing the LD to about half output power and AC coupling the RF signal into it while the receiving PD is fed into a choke or matching transformer is a good enough starting point. If you're very curious I can dig out some old notes, from memory the LD liked seeing <50 ohms and the PD wanted to see >50 ohms.The professional RF over fiber units usually are not much more sophisticated. Opening some up, all that was inside besides DC biasing circuitry was a couple MMICs. I have not tried to push this concept beyond a few hundred MHz; at ~1.5GHz I'd expect considerable gains from reverse biasing the PD or, otherwise, matching out the junction capacitance. Overall end to end noise figure for a fiber link isn't terrible but plan on a good amount of gain and bandpass filtering prior to modulating the LD.