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Third generation all solid state Riometers have been made by La Jolla
Sciences (www.lajollasciences.com)
since 1973. The design was developed at UCSD under a grant from the Office
of Polar Programs of the US National Science Foundation. The initial design
emphasized low power, rugged reliability and simplicity of function. Over
the years these concepts have been proven to be successful at installations
throughout the world. Total production to date is 320 units along with
accompanying antennas and test RF noise sources.
During the 36 years of production, vast developments
have taken place in electronics technology. LJS has incorporated some of
these to improve system performance particularly in the receiver portion of
the instrument. Frustratingly, some components have become obsolete and
have had to be replaced by others of different shape and size and function.
Each time, the circuit boards have been ‘patched’ to accept the new devices
resulting in increased hand manufacturing and related extra labor effort.
With the pending closure of LJS, it is time to consider
the future since there remains a demand for new Riometers in both the wide
beam and imaging system configuration, and a demand for continued
maintenance services for existing Riometers in the field.
These notes are intended to provide a framework to
develop a plan for the replacement of the LJS series of equipment hopefully
in a format which will last another 30 years without serious component
substitution.
FIRST PRINCIPLES
These essential concepts would continue to be the foundation of a new
design:
Small, low power, rugged, reliable and
shippable
Wide range of operating temperature (Polar use)
Minimum switches and connectors for maximum reliability of field
data.
GENERAL
Since the Riometer system involves several electronic disciplines, it may be
practical to divide the work into sections so that different groups could
contribute to producing a fourth generation system. Eventually though a
single assembly location would need to be established for production,
marketing, and maintenance purposes.
RECEIVER SECTION
Critical parts for the first LJS receiver became
obsolete about 10 years ago. The current receivers are manufactured by
Radio Technology in Australia but unfortunately the main integrated circuit
for that design is also no longer available.
Any new design would presumable have a small parts
count (Receiver on a chip?) and parts with a future should be chosen. A
wide band (250 KHz) low noise design is called for with CW sensitivity down
to at least -125dbm. A range of bandwidths choices should be available and
the design for various operating frequencies worked out.
CONTROL BOARDS
Two types are in current production:-
- Simple control board (Model SI). This section
incorporates the RF switching, noise generator and phase detection for
the Ryle-Vonberg system used in all Riometers. It is mainly for IRIS
use where automatic timing and calibration is not practical.
- Full control board (Model SSR). Adds an automatic
calibration system and accurate time marking to the simple control board
for stand alone wide beam Riometers. New logic gates and timing clocks
would be needed since the current ones (CMOS) are no longer readily
available.
ANTENNA
The LJS developed double dipole wide beam design incorporates a unique balun
and a rugged connector block to ensure reliability in all weathers. A
machine shop could be utilized to produce quantities of the connector block,
but otherwise hand manufacture is needed.
RF NOISE SOURCES
- The present LJS servo and test noise sources have
been basically unchanged for 36 years except for incorporating some SMT.
Components continue to be available. Since the noise transistors are
used ‘off label’ they must be purchased in quantity and suitable ones
selected.
- A portable battery operated noise source
(Dial-a-Noise!) has been made for 36 years with little modification.
This design could be continued also, but selection of the noise
transistor is required. The selection criterion is different from that
of the Riometer noise generators. This portable unit is invaluable in
the field and in the laboratory, and has an output greater than the
maximum sky noise expected for full range testing. Units need to be
returned to the factory for recalibration after 3years or so as the
batteries fail.
- LJS has also developed a reference thermionic
noise source with servo controlled selectable noise level in the VHF
band up to 10,000K. All LJS Riometers and portable noise sources are
referenced to this standard.
TEST EQUIPMENT NEEDS.
A Riometer manufacturing and test facility would need the following test
equipment in addition to normal oscilloscopes, voltmeters etc.:-
a. CW signal generator with
sufficient shielding to be usable below -125dbm (hard to find!)
b. VHF vector voltmeter for
noise source and receiver matching and for antenna balun manufacture.
c. Standard noise source as
above.
d. Portable noise source as
above for full dynamic range testing.
e. Switchable VHF attenuator
to -40db in 1db steps.
f. Riometer test jigs for
both bench and field use to isolate the servo loop.
EXISTING RIOMETERS
Since 320 Riometers have been supplied world wide, a service facility needs
to be established to deal with occasional failures of the units. LJS should
gradually withdraw from this responsibility in the next few years.
SUMMARY
36 years ago UCSD received a major grant from the NSF to fund a third
generation Riometer. It now seems that we need another award to establish a
fourth generation machine for the next 30 years. Apparently (re. Volodya
Papitaslivili) NSF has a grant program called “Small Business Innovative
Applications” (SBIA) which might be tried for this, or perhaps OPP may be
willing to fund another development since the majority of Riometers are used
in the polar regions.
If different groups undertake the task of developing
the various sections, there would need to be a coordination effort to decide
on the final configuration. Eventually there would need to be a single
manufacturing facility probably in private hands as at present. At this
time I would be willing to be a consultant to the new groups as development
takes place over the next 2-3 years.
The possibility exists that the Riometer system could
be changed dramatically in ways I have not anticipated, however the
principles I have listed here have stood the test of time and should be
thoughtfully recognized.
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