What is benefit of upgrading from 1m dish to 2.4m dish for hydrogen line?
This analysis is for a friend who has made this upgrade. The largest diameter dish we are currently using at LRO is 150cm dish made of 6 petals – soon to be changed to a solid 160cm dish. It is likely 160cm will be the largest we use for a while, although we do have in storage 180cm petal dish.
Andy
BELOW IS A RESPONSE FROM CHATGPT:
Note the following Wolfgang’s comment on this ChatGPT answer, before reading the ChatGPT response.
There is one important effect which ChatGPT misses:
Hydrogen emission is an extended source. Therefore, you also need to consider that a smaller dish is looking at more hydrogen due to its wider beam width. Because of that, the power does not scale with the collecting area of the dish. In fact, if Hydrogen would be evenly distributed over the sky, the received power would be independent of the dish size. So “1.Sensitivity increase” from ChatGPT is not true for hydrogen emission. It would be valid for sources where their diameter is less than the beam width of the antenna, though.
Other than that, the main benefit of having a higher resolution remains vaild.
Best regards,
Wolfgang
Upgrading from a 1-metre dish to a 2.4-metre dish for 1420 MHz hydrogen-line work brings several big improvements. The gains are mainly in sensitivity, signal-to-noise ratio, and angular resolution.
Below is a clear breakdown:
1. Sensitivity increase (~5.7× more collecting area)
Dish sensitivity scales with collecting area, which goes as πr².
- 1 m dish area ≈ 0.79 m²
- 2.4 m dish area ≈ 4.52 m²
Area ratio ≈ 5.7×
This means:
- You collect ~5.7 times more power from the hydrogen-line emission.
- Your signal-to-noise ratio improves by about √5.7 ≈ 2.4× (if system noise stays similar).
This is the biggest real-world benefit:
► Weaker sources become detectable, and integration times shorten dramatically.
2. Better angular resolution (~2.4× improvement)
Beamwidth is roughly:
θ ≈ λ / D
At 1420 MHz, λ ≈ 0.21 m.
- 1 m dish → beam ~12°
- 2.4 m dish → beam ~5°
So you get:
- Sharper beam, less spillover
- Ability to distinguish finer structure in the hydrogen profile
- Less sensitivity to unwanted off-axis noise sources
3. Lower noise from spillover and ground pickup
A larger dish has a:
- narrower illumination pattern from the feed
- reduced ground spillover
- lower effective noise temperature
This helps the system temperature (Tsys) drop, improving SNR further.
4. Faster, cleaner integrations
Because you start with higher SNR:
- You need less integration time for the same quality spectrum
- Or you can integrate longer but achieve much cleaner line profiles
- Baselines become smoother
- Drift-scan results are significantly improved
5. Ability to detect more subtle astrophysical structure
With a 2.4 m dish you can:
- Resolve Galactic rotation curves more clearly
- See multiple velocity components in the Milky Way more distinctly
- Detect structure in the hydrogen layer that a 1 m dish has trouble separating
Many Radio JOVE-type feeds and simple LNAs perform noticeably better when paired with larger apertures for this reason.
Summary
Upgrading from 1 m → 2.4 m gives:
| Improvement | Factor |
| Collecting area | 5.7× |
| Signal-to-noise | ~2.4× |
| Angular resolution | ~2.4× better |
| Integration time needed | ~1/6 for same quality |
| Ability to see Galactic features | Much better |
If you’re doing serious hydrogen-line spectroscopy—especially velocity mapping—the upgrade is a very large step up.