VLF/ELF Goniometer Receiver
A VLF goniometer (direction-finding) receiver, essentially similar to that described by Bullough and Sagredo (
1973) but see also Smith et al. (1979), is operated on a synoptic basis. Until the end of 1993, the data
recording medium was ¼" 4-track analogue magnetic tape, using a tape speed of 9.5 cm s 1.. The goniometer
output was low-pass filtered at 11 kHz before recording, to avoid cross-modulation between strong VLF transmissions
above 10 kHz, occurring in the tape recorder. The dynamic range was about 40 dB (limited by the analogue
tape recorder). A second band, typically 15-25 kHz, was frequency translated down to 0-10 kHz for recording
on a second tape recorder. Although containing few magnetospheric signals of interest, this band is useful
for measurements of time-dependent perturbations of sub-ionospherically propagated VLF transmissions. Such
measurements provide an indication of irregularities and gradients near the reflection height in the D-region,
on or near the propagation path between transmitter and receiver. A subset of these transmissions is recorded
by the more specialised Trimpi receiver.
From 1994, analogue recordings will be superseded by digital recordings
using the digital audio tape (DAT) format, with a bandwidth up to 22 kHz and dynamic range of about 90 dB.
This will overcome the limitations which were inherent in the previous system.
Recordings are normally
made for 1 minute every 15 minutes (05-06, 20-21, 35-36, and 50-51 minutes past the hour). At times of
unusual activity or for special campaigns, alternative schedules of 1 minute recording every five minutes,
or of continuous recording, can be run. A time code (IRIG-B) and phase stable reference tone are also recorded
on the tape.
Control of the tape recorders is through the Mk-2 AVDAS (Advanced VLF Data Acquisition System);
this supersedes the Mk-1 AVDAS (Smith and Yearby, 1987), and uses modern digital signal processing technology.
Using AVDAS, short sections of the broadband signal (north-south and east-west components separately) may
be digitised as a time series at 16 bits per sample, with a bandwidth up to 20 kHz.
More information and data.
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