# Enhancing Meteor Observations with Photodiode Detectors
## 2 Existing Instruments  
A review of the current literature reveals several conference papers relevant to this study. For instance, in [14], the authors developed a device for radiometric data acquisition with a large dynamic range (meteor apparent magnitues within [\(-\)4, \(-\)20]) and a sampling frequency of 1000 samples per second. This setup employs a single Hamamatsu S1337-1010 BR photodiode (Hamamatsu Corporation, Bridgewater, NJ, USA) with a 100 mm\({}^{2}\) photosensitive area, a spectral response range of 340-1100 nm, and a peak at 960 nm. A logarithmic converter ADL5304 by Analog Devices (Norwood, MA, USA), interfaced with a 24-bit resolution sigma-delta A/D converter, ADS1255 (Texas Instruments, Dallas, TX, USA), was used to amplify the photodiode signal. However, the authors did not include an electrical schematic. The device's operation was tested only through the acquisition of radiometric data from a single event lasting 0.9 s without simultaneous camera imaging. This limitation prevents correlating the recorded time sequence with the actual event, which is crucial given the high variability and peaks observed in the data (suggested to be from multiple successive strikes). Additionally, the authors attributed the 50 Hz oscillations in their data to streetlight illumination, but these could also result from measurement path disturbances (e.g., poor voltage filtering, external interference, lack of shielding). The absence of a time sequence with the photodiode fully covered is a missed opportunity to analyze the system's intrinsic noise sources and values, essential in such applications. Despite these issues, the authors expressed hope for further development of this intriguing initial prototype in their conclusion. Another solution presented in a conference paper should be regarded as a description of the challenges encountered during the development of a large dynamic range and very fast radiometer [15]. The system employed 16 cheap BPW34 photodiodes, each with a radiant sensitive area of 7.5 mm\({}^{2}\). These diodes were divided into four groups, with each group containing four elements connected in parallel. Transimpedance amplifiers were used to convert the current from each group. Subsequently, the output signals from the four transimpedance amplifiers were summed using an operational amplifier with a fixed gain, operating in an inverting configuration. In the final part of their paper, the authors emphasize that the radiometer is still under development, primarily due to the low signal-to-noise ratio. They suggest that more effective isolation between the analog and digital parts of the system could be a solution. While this is true, the influence of noise from components such as resistors, photodiodes, and operational amplifiers cannot be overlooked in such designs. The presented solution is suboptimal in this regard. In each of the four channels, 10 M\(\Omega\) resistors were used to convert the photodiode current to voltage. Importantly, the thermal noise of these resistors is typically the dominant component (see Section 3.3). Given that this multi-channel system sums the output signals of each transimpedance amplifier, the noise characteristics of the solution are very unfavorable (it is unfortunate that the output signal with complete darkness was not presented, as it could shed light on this issue). Additionally, it is worth noting that the system has a fixed gain, which adversely affects the ability to observe low-intensity phenomena (while high gain increases sensitivity, it leads to the saturation of the output amplifier, a problem discussed in Section 3.2). The potential for building a low-cost system for radiometric observations of meteors is the focus of another conference paper by [16]. This case involves an early-stage prototype. The device uses a single BPW34 photodiode, an Arduino Uno board, a data acquisition module board with a 16-bit A/D converter (AD7705), and a simple transimpedance amplifier based on the LMC6462 component (Texas Instruments, Dallas, TX, USA).