X-band receiver on 20 m Green Bank telescope

[Dimitry UA3AVR]

Hi everyone.
Now the X-band receiver 8000-10000 MHz is switched on. Skynet does not accept observations in L-band. May be somebody knows for how long?

P.S. May be also somebody knows interesting objects for observations in the X-band.

Regards, Dimitry UA3AVR.

[Andrew Thornett]

This is what ChatGPT suggests......does anyone know which of these are practical with 20m?

The X-band (roughly 8–12 GHz) is a surprisingly rich part of the radio sky—less crowded than lower frequencies but still full of interesting natural and artificial signals. Since you’re working in radio astronomy, this band sits in a sweet spot between atmospheric transparency and compact high-energy sources.

Here are some of the most interesting things you can observe:

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🌌 Galactic & Extragalactic Sources

Supernova Remnants (SNRs)

• Strong synchrotron emitters → still bright in X-band
• Key targets:
• Crab Nebula
• Cassiopeia A
• Good for studying spectral index changes (compare with L-band)

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Active Galactic Nuclei (AGN) & Quasars

• Compact, bright, often variable
• Ideal for interferometry (you mentioned using RSPduo)
• Examples:
• 3C 273
• Cygnus A

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🌠 Galactic Emission

H II Regions & Star Formation

• Dominated by free–free (bremsstrahlung) emission
• Smooth spectrum → still detectable at X-band
• Example:
• Orion Nebula

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Galactic Plane Continuum

• Diffuse synchrotron + thermal emission
• At X-band:
• Less synchrotron dominance than lower frequencies
• Cleaner view of thermal components

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🪐 Solar System Objects

The Sun (when active)

• Produces microwave bursts during flares
• Strong enough to saturate sensitive setups
• Great for dynamic monitoring

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Planets

• Jupiter
• Mostly quiet at X-band (its famous decametric bursts are much lower freq)
• Weak thermal emission detectable with good setup
• Venus
• Strong thermal microwave emitter (thick atmosphere)

---

🛰️ Artificial Signals (Very Strong!)

Satellites & Spacecraft

• X-band is heavily used for:
• Deep space comms (e.g., NASA DSN)
• Weather satellites
• Radar systems
• You’ll easily detect:
• Passing satellites (Doppler shifts are fun to track)
• Occasional spacecraft carriers

---

📡 Special Techniques Worth Trying

• Continuum mapping
  Scan across the Galactic plane → measure brightness variations

• Spectral index experiments
  Compare X-band vs your 1420 MHz setup

• Interferometry targets
  Bright compact sources (e.g., 3C catalog) are ideal

• Atmospheric studies
  X-band is sensitive to:

• Water vapor
• Rain fade (useful calibration experiments)

---

⚠️ Practical Reality Check

• Hydrogen line (1420 MHz) → not in X-band
• You’ll mostly be doing continuum radio astronomy, not line spectroscopy
• Dish size matters more here (shorter wavelength → narrower beam)

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Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Dimitry UA3AVR <ua3avr...@gmail.com>
Sent: Thursday, May 14, 2026 9:17:44 PM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] X-band receiver on 20 m Green Bank telescope

 

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[Dimitry UA3AVR]

Thanks, Andrew ... it seems the natural objects are mostly of continuum spectra. Cas A, Tau A are of measurable fluxes ~500-600 Jy in this frequency band. For spectral observatins, there exists a cyanoacetylene molecule HC3N, see fragment of table from Wilson, Rohlfs, Hüttemeister, Tools of Radio Astronomy, 2013, with relatively high Einstein coefficient A, but it seems rare.

четверг, 14 мая 2026 г. в 23:37:07 UTC+3, Andrew Thornett:

[Ayushman Tripathi]

Hi Dimitry,

Here's the info I found on HC3N targets:

• Sgr B2: the strongest HC3N emitter in the sky, this is the original Turner 1971 detection. The J=1-0 line shows weak maser action.

• TMC-1: cold dark cloud (Tk ~10 K), cyanopolyyne-rich. Plenty of J=1-0 literature on this one.

Good paper covering both as HC3N targets (and many more): https://adsabs.harvard.edu/pdf/1976ApJ...205...82M (Morris et al. 1976 multi-source survey)

Also worth a shot: Orion-KL, DR21, IRC+10216 (carbon-star envelope).

Here's a plot of relative abundances of HC3N for TMC-1, Orion Ridge, and IRC+10216 from Wilson / Rohlfs "Tools of Radio Astronomy" that I got this month and really enjoying it:


X-band RFI to dodge (NRAO list: https://science.nrao.edu/facilities/vla/docs/observing/RFI/X-Band):

• 9300–9900 MHz: SAR satellites + airborne weather radars

• 10740–11600 MHz: terrestrial microwave links

• 11700–12000 MHz: continuous strong RFI along the geostationary belt

The HC3N line at 9.098 GHz sits just below the SAR band at 9.3 GHz, so it's in one of the cleaner spots in the band.

BTW, HC3N is also observable at higher transitions, J=2-1 at 18.2 GHz, J=3-2 at 27.3 GHz, J=4-3 at 36.4 GHz, etc., spaced ~9.1 GHz apart all the way up to sub-mm.

Thanks!

Ayushman

[Dimitry UA3AVR]

Thanks, Ayushman, for nice investigation. 

The paper reference, the abundance plots, and the RFI analysis are very helpful. Unfortunately, the telescope is currently not operating in high-resolution mode needed for spectral observations; Skynet returns an error when attempting to configure high resolution. TMC-1 and Sgr B levels are strong in comparison to others; nevertheless, detecting them requires at least 500–1000 seconds of tracking (their brighness temperatures ~ hundreeds of mK, thanks to ChatGPT). Also, these are rather expensive observations: one second costs one credit, and the current balance of the SARA account is about 2000 credits.

Many regards, Dimitry UA3AVR.

суббота, 16 мая 2026 г. в 02:25:44 UTC+3, Ayushman Tripathi:

[Dimitry UA3AVR]

Here is the reference with level estimations: https://chatgpt.com/share/6a080faf-f854-8384-b759-b3dafa22663e

суббота, 16 мая 2026 г. в 09:04:21 UTC+3, Dimitry UA3AVR:

[Adrian]

Also as Dimitry stated not only is high resolution disabled giving the error message except possibly @ 9 GHz only but the map function portal settings are also suffering from a bug in that at these frequency's , the estimated beam width is ~0.13°, so Nyquist sampling for a scan requires a sweep spacing of roughly 0.04°. However, the raster UI portal selection does not allow dgree settings and only allows for beamwidth gaps and actually result in real setting gap no smaller than 0.10°, regardless of the selected “beam fraction” options even at a 1/10 beam selection. The preset fractions (1/3, 1/4, 1/5 beam) all resolve to fixed values around 0.20–0.33°, which are far larger than the actual beam. Thus a map setting that should be giving a raster of 13-18 passes are only set for 2-4 even though the credit charges are for the higher number. I've tried to report this problem but only expect a response sometime after the estimated half life of the proton or possibly that of the heat death of the univerese from them.

Adrian