2026
Admin
Online interdigital RF cavity filter designer
Dale Hitherington’s online calculator (WA4DSY): https://www.wa4dsy.net/cgi-bin/idbpf
Alex Pettit’s new RFI removal regime in H-Line 3D
New process to clean up hydrogen line data, removing RFI. https://github.com/AP-HLine-3D/HLine3D/blob/main/JAVA_HL3D_mX%2Bb_RFI_V2.2_08Mar26_IFAvg2csv.jar start with zero frequency width and gradually widen.
Tell me what a SID (Sudden Ionospheric Disturbance) is and what range of frequencies are covered when monitoring for SIDs.
A SID stands for Sudden Ionospheric Disturbance. It refers to a rapid change in the ionosphere caused by intense solar radiation, usually from a solar flare. These disturbances are commonly…
Are there disadvantages of using SAWBird H1 vs Cavity filter?
Yes — there are several practical disadvantages of using a SAWBird H1 (or similar surface-acoustic-wave bandpass filter) compared with a cavity filter in RF front-ends, especially at VHF/UHF, narrow-channel, or…
Can I use cavity filter followed by amplifier to get better effect than SAWBird H1?
Amplifier examples relevant to discussion below of receiver chains that involve amplifier before a cavity filter: Budget amplifiers: Better quality amplifiers: Even better and more expensive amplifiers: Description: Yes —…
Very simple antenna/feed adjustment that can increase received power by ~3–6 dB
A surprisingly effective improvement for hydrogen-line reception is optimising the feed illumination of the dish. Many amateur systems lose several dB simply because the feed does not illuminate the reflector…
One upgrade that often improves hydrogen-line observations more than adding extra amplifiers or filters is improving the frequency stability of the SDR.
One upgrade that often improves hydrogen-line observations more than adding extra amplifiers or filters is improving the frequency stability of the SDR. Use a stable reference (TCXO or external clock)…
A trick many hydrogen-line observers use with the SAWBird H1 that improves SNR by 2–4 dB without adding hardware.
A simple improvement many hydrogen-line observers use with the Nooelec SAWbird+ H1 can noticeably improve the received SNR without adding another filter. The trick: Reduce gain at the SDR input…
Would adding an 1415-1425 MHz cavity filter before Nooelec SAWBird H1 improve the signal received at SDR?
Short answer: sometimes yes, but only in specific situations. In many hydrogen-line setups it gives little improvement and can even slightly reduce sensitivity. What the SAWBird H1 already does The…