The OpenStint Loop Preamplifier Board is an optional front-end module, designed for the OpenStint Laptimer System. It provides signal conditioning and amplification for the parallel-wire "antenna", ensuring clean, stable, and maximized signal transfer to the timing receiver.
- Fully compatible with the OpenStint timing receiver interface. Operated from the bias-tee available on HackRF One and RTLSDR.
- Output is matched to 50 Ohm.
- +12 dB gain low-noise amplifier
- Fits Hammond's 1590L-style aluminium cases
- Power pin available for 1S batteries (remove
L6orFB2in this case, or add DC-block capacitor before the SDR). - Open hardware design – schematics and PCB available under permissive license
- Directly manufacturable at JLCPCB (LCSC part codes provided).
The loop preamplifier is built around 4 key functional stages:
-
Balanced–Unbalanced Conversion
Converts the differential loop input into a single-ended signal. It has some input protection that can also clamp the input signal in case of close transmitters. -
Matching Network
Optimizes impedance matching between the loop and the amplifier for maximal power transfer and improved sensitivity. -
+12 dB Low-Noise Amplifier (LNA)
Boosts the signal with minimal added noise, ensuring reliable lap detection even under low signal conditions. -
Band-pass filter SDRs unfortunatelly downconvert out-of-band signals to basebands (like harmonics of LO). This filter does some justice, and is probably the most important contribution of this preamp board.
Add an optional 75 Ohm output as well, or add a separate 50 to 50+75 splitter. This hardware change should have a software counterpart, which reads both the OpenStint and MyLaps decoders, and merges the results into a single stream for laptiming applications. We could keep both open and commercial transponders to co-exists on the same track this way. Also, upgrading post-4.4 firmware won't be such a headache neither.
Automatic gain control: even a simple one could increase the dynamic range of the decoders.
Part of the OpenStint Laptimer System – open, modular, and precise RC timing.