The Pisgah Low Frequency Monitor



Overview: The Pisgah Low Frequency Monitor (PLFM) is a system for surveying the radio frequency spectrum below 100 MHz at the Pisgah Astronomical Research Institute (PARI), a remote observing site south of Asheville, NC. This survey will serve also as a pilot experiment, quantifying the suitabilty of this site for important low frequency science including transient surveys and study of the 21-cm emission associated with the Epoch of Reionization (EoR).

Maintainer: S.W. Ellingson
This page is http://www.ece.vt.edu/~swe/PLFM/
Last Updated: June 5, 2004 1128 EDT


June 5, 2004: A Pair of Solar Bursts

Click on picture for high resolution version.

Here's a picture of a pair of solar radio observed and confirmed in the PLFM data, from June 2. There are two distinct events: One at 2300 UT and another at about 2315 UT (see high-resolution figure for time index). These same events can be seen in data from the GBSRS in Green Bank, WV. See comments below about difference between the time-frequency resolution of the GBSBRS and the PLFM.


June 4, 2004: First Solar Radio Burst Spectragram

Click on picture for high resolution version.

Here's a picture of the first solar radio burst to be observed and confirmed in the PLFM data, from June 1, about 1830 UT (see high-resolution figure for time index). This same event can be seen in data from the GBSRS in Green Bank, WV. Note that the time-frequency resolution in the PLFM spectragram is 195 seconds (we're doing deep integration here) and 610 Hz (for resolution of narrowband RFI), whereas the resolution of the GBSRS is a few seconds and tens of kHz. (Clearly, if the intended use of the PLFM was solar radio, we would want to adopt the GBSRS configuration!) Another issue is that the shape of the 4 MHz passband has not been corrected in the PLFM image, which accounts for the apparent spectral ripple. Also worth noting in the spectragram is the Galactic background noise, which is prominent below 35 MHz in this spectragram.


May 27, 2004: First Look

The First 328 Milliseconds

Click on picture for high resolution version.
Here is a first look at 26.5-89.5 MHz with 610 Hz resolution. This is a single sweep stitched together from the flat central portion of the passband after each tuning. The effective integration time is 328 ms. The input to the receiver has been deliberately padded down (attenuated) to the point where the Galactic noise spectrum is just barely visible rising towards the low frequency end of the plot: The notion is that this yields the highest linearity that can be achieved with useful (Galactic-noise-dominated) sensitivity. This minimizes the extent to which self-generated intermodulation can enter into integrated spectrum. The monster signal straddling 70 MHz is TV Channel 4. The video and audio carriers from Channels 2, 3, 5, and 6 are all clearly identifiable, although much weaker. Although difficult to see due to the resolution of this image, FM carriers are identifiable in every 200 kHz allocation from 88.1-89.3 MHz. It should be noted that the extreme sensitivity and resolution of this measurement make the situation look worse than it actually is: In fact, the vast majority of the 104,858 spectral channels shown here exhibit no detectible interference.


May 22-23, 2004: Installation

Antenna

Click on picture for high resolution version.
The "big fat droopy dipole" and active balun (barely visible near the feedpoint) is of the original vintage created by Bill Erickson and the Low Frequency folks at the U.S. Naval Research Laboratory (NRL). The copper dipole arms and the active balun unit were provided by NRL.

Receiver/Console

Click on picture for high resolution version.
The receiver and console are located in Building 28 on the PARI Campus, separated by 300 feet of cable. The current receiver (2nd shelf from the bottom) is an "up/down-converter" tunable from about 10 MHz to about 150 MHz, outputing an I/Q baseband signal 4 MHz wide. I and Q are digitized with 12 bits at 10 MSPS using a PCI-based digitizer card and are acquired and analyzed using software written in C running on Windows XP Pro. Complete "as if you were there" access to the PC is possible via an internet connection.