La Jolla Sciences - Report on Riometers, 2004
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  La Jolla Sciences  
 


REPORT  ON RIOMETERS,  JULY 2004


 
 

 

Dear Colleague:

We are pleased to report that we have in the last few years incorporated significant improvements to the original 1973 design of our instruments.   Although steady improvements have been made to the control unit over the 31 years we have been making Riometers, we have now completely modernized the receiver portion of the Riometer.   In a joint project with Ian Bird of Radio Technology, Melbourne, Australia, we now offer a Riometer with much better rejection of out-of-band interference.   This has been accomplished using ceramic filters and modern integrated circuits.

DESIGN IMPROVEMENTS:  The new receiver has a significantly sharper bandpass at the operating frequency giving a greater rejection of interference on adjacent frequencies plus better rejection of frequencies near the intermediate frequency (IF) of 10.7MHz.  Specifically, with a -3db passband of 250KHz, the rejection at   ±0.5MHz about the center frequency is at -80db (was -40db).    IF rejection is now at -100db (was -60db).   Users of Riometers will appreciate the superiority of the new design for observing absorption in difficult locations (and most locations are difficult for Riometry!).  Note that any of our older Riometers can be improved by installing the new Receiver.

There has been a significant increase in the use of Riometers worldwide for measurements of Ionospheric Absorption using the imaging technique (IRIS) first implemented by Professor Rosenberg and his colleagues at the University of Maryland.   Although many groups still use the Riometer in synoptic wide beam observations, there are more and more units incorporated into sophisticated systems involving multiple beams.  Since the latter type is rapidly switched from beam to beam, it was necessary to develope a model of the Riometer (Model SI) in which the self calibrating and timing sequence were deleted.   The standard model (Model SSR) complete with calibrations and time markers is still available for conventional (mostly wide beam) installations.

During the development of the Riometers for the first imaging system, it was necessary to further decrease the integrating time constant from the 0.25Sec which had become standard to as little as 5mSec with particular emphasis on a symmetrical response to both increasing and decreasing absorption.  Because of this we are now able to offer these options as an upgrade to many of the Riometers we have manufactured in our 31 year history.  In addition, some of our earlier Riometers need to be upgraded to include improved time constant and/or its symmetry, power linearity and dynamic range.  Our current production Riometers achieve maximum theoretical dynamic range.

We are pleased to attach a new price list.    Note that we have included prices for upgrading units to the new receiver design, plus prices for upgrading older control boards.  Please contact us if you need further clarification or if you wish to discuss special modifications for your observing objectives.

                                                                                                With warm regards,

                                                                                                Hugh Chivers

 
 
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