ETA RFI Survey: Sep 10, 2005

Overview: Shown here are the results of a quick-and-dirty measurement of RFI at the PARI Building 17 site on Sep 10, 2005.

Maintainer: Steve Ellingson (Virginia Tech)
This page is
15 Sep 2005 UT 0900. Initial posting.

The measurements were conducted using our Radio Shack discone antenna, held at about head level just outside the west-facing door of Building 17 at PARI. The measurements were performed mid-afternoon on Saturday, September 10, 2005. The discone is connected to about 10 feet of RG-58, which in turn is connected to a Rhode & Schwartz FSH3 handheld spectrum analyzer. The spectrum analyzer is connected to a laptop via optical RS232, and data is acquired using a C-language program written by the author. Each plot below represents just a few minutes of elapsed time observed with a low duty cycle of acquisition (i.e., most of the elapsed time is spent moving data, as opposed to observing), with the spectrum analyzer set to "sample" (as opposed to "autopeak") mode detection to facilitate meaningful averaging. The antenna is being moved over a linear span of about 5 feet during the observation in an attempt to capture magnitude variations due to multipath scattering, should it be a factor (it usually is).

5-95 MHz, 300 kHz resolution. In this very wide spectral view we see the three main threats to receiver linearity at this site: HF transmissions below 30 MHz, TV Channel 4 straddling 70 MHz, and the FM band starting just above 90 MHz.
23-53 MHz, 100 kHz resolution. This view is approximately the same as the ETA frequency span, 29-47 MHz, and so represents what we have to deal with as "in-band" RFI. The signal just above 40 MHz is believed to be the local state police 2-way radio.
37.45-38.35 MHz, 3 kHz resolution. This narrow view conveys a sense of what ETA will see at its maximum spectral resolution (probably about 15 kHz). This view also contains the 37.5-38.0 MHz and 38.0-38.25 MHz bands where Radio Astronomy has secondary and primary allocations respectively in the U.S.