Receiver Lab Talks: 2025
Questions: Edward Tong
Time: Thursday 12:00 PM EST/EDT
Where: M-340/Zoom
| Date | Speaker | Title | Summary |
|---|---|---|---|
| Feb. 27 | Jim Moran CfA |
The Origins of Very Long Baseline Interferometry in Radio Astronomy | In this talk, I will describe the origin of the idea that the image of a radio source can be built up from the fringe visibility measurements of a two element interferometer, as first demonstrated by Michelson in the 1920s. The achievable resolutions at radio wavelengths were limited to about 0.05" in the early 1960s, but an amazing confluence of the technological developments of television recording technology, precise atomic clocks and fast digital computers made possible the formation of coherent interferometers with arbitrarily large element separations. Angular esolutions have been pushed down to 25 microarcseconds over more than 50 years of development. |
| Feb. 20 | Laura Fissel Queens Univ., Canada |
Very Long Baseline Interferometery from the Stratosphere: The Balloon-borne VLBI Experiment (BVEX) | The resolution of ground-based Very Long Baseline Interferometry (VLBI) is limited in baseline by the size of the Earth, and in observing frequency by the molecular absorption of the atmosphere. While space missions are extremely costly, balloon-borne VLBI would give access to frequencies beyond those of the Event Horizon Telescope (EHT) at a fraction of the cost. As a first proof of concept for balloon-borne VLBI, the Balloon-borne VLBI Experiment (BVEX) will launch as part of the Canadian Space Agency's (CSA) Stratos program from Timmins, Ontario, Canada in August 2025, operating above more than 99% of the Earth's atmosphere. This experiment consists of a K-band 22 GHz radio telescope and receiver, where the signals will be correlated with simultaneous observations made by the Very Large Baseline Array. In this talk we will give an overview of the telescope, receiver, and backend as well as technical challenges such as position tracking and timing reference stability that arise when attempting VLBI from the stratosphere. To wrap up, we will talk about how lessons learned from BVEX will help in designing a mm/sub-mm VLBI mission in the future, which could improve the uv-coverage of VLBI networks such as the EHT or next-generation EHT (ngEHT). |
| Feb. 13 | Liam Connor Harvard |
Large-N Small-D Arrays at ~1 GHz | Radio astronomy at GHz frequencies is uniquely coupled to Moore's Law. Modern interferometers are computational cameras, driving survey telescopes towards the large-N small-D paradigm. I will discuss two proposed radio telescopes. The first is the 2000-antenna deep synoptic array (DSA-2000), which will map 3 pi sr of sky between 0.7 and 2 GHz at unprecedented speed, with commensal HI, pulsar, FRB, and continuum surveys. The second is a concept for a "coherent all-sky monitor": a dense aperture array that will find the brightest FRBs from the local Universe. While these projects are at different stages and are of disparate scales, they have a number of key technologies in common. On the all-sky monitor, I welcome ideas, advice, and engagement! |
| Jan. 30 | Sara Issaoun CfA |
Frequency Phase Transfer for (sub)millimeter VLBI | Frequency Phase Transfer (FPT) is a key technique to increase coherence and sensitivity in radio interferometry via the use of non-dispersive phase solutions derived at lower frequencies to calibrate higher frequencies. While this technique, pioneered by the Korean VLBI Network, is readily used at frequencies under 130 GHz, it remains largely untested in the (sub)millimeter regime. Over the last two years, an effort has been made to outfit dual-band systems at (sub)millimeter observatories participating in the Event Horizon Telescope (EHT) and to test the feasibility and the performance of FPT up to the 1.3mm observing wavelength of the EHT. In this talk, I will present the status and results of simultaneous dual-frequency VLBI observations carried out and the applications of this technique to ongoing and future projects. |
| Jan. 16 | Edward Tong CfA |
Receiver Linearity Considerations: How to measure gain compression accurately | Astronomical receivers typically handle very weak input signals. With the development of ultra-wideband receivers and the neccessity to calibrate them using a relatively warm black body, there is a risk that the receiver may operate outside its linearity range. The most prevalent issue is gain compression, which occurs when a receiver component's gain is reduced by large input signals. In this presentation, I will detail a technique for accurately measuring low-level gain compression in both amplifiers and mixers, ensuring the linear operation of receivers |
Previous presentations available here:
CfA managed Google Drive
