Alan E.E. Rogers, Heidi Johnson
(Email from Alan E.E. Rogers on August 25th, 2018)
Thank you all for participation in the 21-cm Systems Workshop at Haystack 23/24 August 2018. Judd, Raul and I found the talks, discussion and interactions extremely useful. A lot was earned about how to improve the 21-cm systems with the goal of finding the true global absorption and agreement between different systems.
The files containing the presentations are available at:
and the password is ‘workshop’.
Here are some notes we made:
Tests for EDGES:
- Try to combine low, mid and high-band data in some way to increase frequency range.
- Consider different functional forms of absorption signature.
- Understand why best fit at midband has less flattening.
- Rent a Ground Penetrating Radar (GPR) for more information on ground at MRO, OVRO and Marion.
- Need spectrum analyzer at the MRO for better check of RFI leakage from the backend and ADC plus measurement of the RFI leakage from hut.
- Measure the S11 looking into the receiver to check dependence on LNA input connected to short, open and load to check for sufficient reverse isolation to ensure cable ripple is canceled by 3-position switching.
- Cynthia suggests rotating antenna 45deg, and try different digital spectrometer.
- Thermal improvements: LEDA finds better Alan variance when minimize air in thermal controlled volume (convection).
- Foreground fitting: GMOSS analysis by SARAS says 5 or 6-terms needed.
- LEDA uses a solid state switch from mini-circuits that is not listed in catalog – ask Lincoln for details. If EDGES can tolerate more loss in switches future EDGES receivers could use solid-state switches for calibration.
- Hills: We wonder how do double gaussian and chirp models look when poly is increased to more terms? We found that the double Gaussian and chirp models both continue to work with higher-order polynomials.
- 60 MHz feature: We need to go back investigate where (if anywhere) it might have been related to a backend issue. We believe any 60 MHz structure is from the sky in all of our receiver-1 data, but we should try to confirm.
- SARAS-3: may have updates end of September.
- Ionosphere: Another vote (in addition to Hills) to try to remove absorption using GPS data.
Venue: MIT Haystack Observatory, 99 Millstone Road, Westford, MA 01886
Recommended Hotel: Groton Inn, 128 Main St, Groton, MA 01450, 978-448-6600