Comparing specifications of range of software defined radios that can be used for hydrogen line Amateur Radio Astronomy with small dishes.
Detecting the hydrogen line at 1420.4058 MHz is a popular project among amateur radio astronomers, and several software-defined radios (SDRs) are suitable for this purpose when paired with appropriate antennas and low-noise amplifiers (LNAs). Below is a comparison of some commonly used SDRs for hydrogen line observations:
RTL-SDR (RTL2832U)
An affordable USB dongle that covers frequencies up to approximately 1.75 GHz. While cost-effective, it has a higher noise figure and lower dynamic range compared to more advanced SDRs. Suitable for beginners, especially when used with additional LNAs and filters to improve performance.
AirSpy R2
A mid-range SDR offering better sensitivity and dynamic range than the RTL-SDR. It covers frequencies from 24 to 1800 MHz, making it suitable for hydrogen line observations. The AirSpy R2 provides higher resolution and better performance for serious amateur radio astronomers.
NooElec SAWbird+ H1
While not an SDR itself, this is a custom LNA and filter designed specifically for hydrogen line observations. It can be used in conjunction with SDRs like the RTL-SDR or AirSpy to enhance their performance by providing a 40 dB gain and a noise figure of approximately 0.5 dB.
RASDR2
Developed by the Society of Amateur Radio Astronomers (SARA), the RASDR2 is a specialized SDR designed for radio astronomy applications, including hydrogen line observations. It offers a wide frequency range and high dynamic range, tailored to the needs of amateur radio astronomers.
HackRF One
A versatile SDR that covers frequencies from 1 MHz to 6 GHz. While it offers a broad frequency range, its performance in terms of noise figure and dynamic range may not be as optimized for hydrogen line observations as the other SDRs mentioned.
Considerations for Hydrogen Line Observations:
- Antenna: A high-gain directional antenna, such as a small parabolic dish (around 1 meter in diameter) or a Yagi antenna tuned to 1420 MHz, is essential for detecting the weak hydrogen line signals. Scribd
- Low-Noise Amplifier (LNA): Using an LNA with a narrowband filter centered at 1420 MHz can significantly improve the signal-to-noise ratio. The NooElec SAWbird+ H1 is an example of such an LNA designed for hydrogen line observations. RTL-SDR
- Software: Software tools like GNU Radio, SDR#, or specialized hydrogen line software can process the received signals and perform spectral analysis. Some software is specifically designed for hydrogen line observations and can interface with various SDRs. GitHub
When selecting an SDR for hydrogen line observations, consider factors such as sensitivity, dynamic range, frequency coverage, and compatibility with LNAs and software. While entry-level SDRs like the RTL-SDR can provide a starting point, investing in higher-performance SDRs like the AirSpy R2 or specialized equipment like the RASDR2 can yield better results for serious amateur radio astronomy enthusiasts.