Date: Thu, 29 Nov 2001 02:34:21 -0800 (PST)
From: "John Sexton" <computernetworks@go.com>
Subject: VLF: TECH: Re:IMAGE Radio Plasma Imager
To: rsgb_lf_group@blacksheep.org
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Hi All, 
I listened/watched with Spectran on 15kHz, for the IMAGE Radio Plasma Imager satellite on 21/24/27th, but nothing seen at all. 

Thanks to Peter G8AFN, I eventually tracked down a more informative web page at: 
http://image.gsfc.nasa.gov/campaign/whistler_campaign.html. 

It appears that the satellite is transmitting with an average power of 30.8 watts in order to measure the
plasma resonance frequencies characteristic of the Earth's magnetophere (3 kHz to 3 MHz). 
The RPI instrument consists of an electronics enclosure, four 250 m wire antennae with 
deployers (including switches and couplers), and a z-axis boom canister containing two 
10 m lattice boom antennae and two preamplifiers. 

The mean period is about 854 minutes, so the mean radius of the orbit is 18,566 miles (29879 km) with an apogee at about 8 Earth Radii and the perigee over the southern hemisphere polar. When IMAGE is near perigee, either inside the plasmasphere or at low altitudes, some of the signals launched between 3 kHz and about 500 kHz may propagate in the whistler mode. An outstanding problem to be investigated under these conditions concerns whistler-mode propagation from an in situ source to the ground. It is not expected that detection of RPI signals on the ground will be a common occurrence, and the conditions under which such detection may occur will be of great scientific interest. 

On that web page a table is given showing where and when to listen for it. This table seems to give different longitudes to those from the Locator page, so I am a little puzzled. However it gives more precise times for the start of the VLF transmissions. For the 27th of November it gave turn-on time as 20.16 and longitude as 359.36, and one location as England. 

In fact on the 27th I listened from 19.30 till 20.47, which was when the transmission was scheduled to end, and despite using longer and longer integration times, saw absolutely nothing. Apparently the radio path was then 1.45 radii, so nearly 6000 miles above my head. Presumably 30 watts is not enough for that distance. 

There is one more opportunity for those of us in Europe : On the 30th November starting at 19.26 UT, it should be over Italy. 

One useful thing that came out of this effort, was a better understanding of the latest version of Spectran, especially the Band pass filter and other filters, which seems to be absolutely excellent, not ringing until one gets down to just a few Hz. It is amazing how it makes it possible to hear signals, that with Argo one can only watch. 

73, John, G4CNN 


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