A half-wave dipole resonant at 1420 MHz (the hydrogen line) has essentially the same impedance as at any other frequency: In practice The actual feedpoint impedance will vary depending on…
What you’re seeing is real, and it surprises a lot of people the first time they map the Galaxy in the 21-cm line. In short: the Galactic centre is not…
Mostly from the optically dark regions between the spiral arms, not from the bright arms themselves. Here’s why that happens, and how it matches what you’re detecting. 1. What the…
Posted by Alex Pettit on SARA Mailing List 18/1/2026: Typical calculation for a one quarter wavelength (1/4 WL) antenna is WL / 4 * 0.95 211 /4 * 0.95 =…
Following results of investigations by Alex Pettit were posted on SARA Mailing List 20/1/2026: The “Nooelec 1.4GHz” feed seems improperly designed : the Focal Point of a 1m f/D 0.35…
That helps a lot — Ptarmigan Triffid immediately explains the confusion 👍 You have not used the wrong antenna, only the wrong band name. Ptarmigan & Triffid (UK Army) The…
Excellent — I’ll go through all four, keeping it practical and tied to 1420.405 MHz H-line work with WR-650. 1. Field patterns in WR-650 at 1420 MHz For the dominant…
Short answer: because different people are talking about different operating regions of the same waveguide, and some descriptions quietly assume single-mode, low-loss, well-matched operation rather than mere propagation. Here’s the…
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