Radio Astronomy SA

A radio receiver, also known as a receiver, is an electronic device that receives radio waves and converts information carried by them to a usable form.  They are an essential component of detection systems that use radio and are usually used with an antenna.  The information being detected may be in many forms such as propagation phenomena, sound, moving images or digital data.  Practical radio receivers perform three basic functions on any signal from an antenna: filtering, amplification and demodulation.  During filtering of radio frequencies, the wanted information is allowed to pass while any undesired signal and noise is minimised or cancelled out.  This may include the complete or partial suppression of some aspect of the signal.  Amplification is the process of increasing the desired output, to partially compensate for power loss during transmission.  At the receiver’s end, the frequency must be carefully amplified to maintain the relationships between the signal's original characteristics.

For the first three spectrometers, ASSA purchased commercial-off-the-shelf (COTS) Callisto Receivers from the e-Callisto PI, Christian in Switzerland.  There are detailed descriptions on the theory, design and operation of both the European variant here and the North American variant here.   Note that the COTS receiver draws ≈260mA @ +14VDC (3.7W) in measurement mode.

Peter chose to build new receivers for our more recent receiver requirements.
It was not too difficult to find an appropriate enclosure to house the Callisto Rev 1.12 printed circuit board (PCB) and the Philips CD1316 Tuner which when installed, towers above it. Altronics Cat. # H0442 is almost a perfect fit for installation of both the PCB and tuner.  This diecast aluminium box with flanged mounting points on the lid, is slightly smaller than the Eurocard style enclosures constructed in the EU and USA.  The size reduction allows us to better use the amount of space available to house our receivers and associated hardware.  Having only one access opening, there is less likelihood of radio frequency interference (RFI) entering or leaving the enclosure.  There is more than sufficient space and structural integrity to mount D-Sub connector(s), power socket(s), LED indicator(s) and switch(s), as required.  The brackets imply, and our images show that there might be a requirement for two power switches, two power sockets and two LED indicators.

There is a CD1316 Tuner option (-P) available where a DC supply can be routed to an LNA, perhaps two LNAs, via the RF Input connector of the tuner.  It appears that this option is only in the horizontal format, not vertical.  The current PCB supports the -P option and provision may be incorporated to do this from a separate power source.  Recently, there have been some units on eBay in Germany, but they don't post to Australia.

We have opted to omit the focal plane unit (FPU) capability but included the D-Sub 25 connector because it would be painful to retrofit, if ever required.  The coaxial connections for the 10.7MHz IF output, Video output and 1MHz clock input have been omitted but would be a simple job to install if either, or all functions are required sometime in the future.  Some effort to minimise conducted emissions on the DC power wiring entering or exiting the receiver case is jammed into the corner in the form of a first order common mode filter for each power connector.

In both of our Phase 3 (MWA) Spectrometers and Phase 4 Spectrometers, each Low Voltage Modification (LVM) Callisto Receiver has been constructed to operate from unregulated power supplies of > +6.5VDC, primarily to reduce the total power consumption of the instruments.  Note that our LVM receivers each draw ≈165mA @ +14VDC (2.3W) in measurement mode (this includes DC-DC converter losses).  The DC-DC converter outputs are set for a +7.5VDC input to the LVM receiver.

There is another section about the Callisto Low Voltage Modifications here.

Peter chose the Noolec NESDR SMArtee XTR over the usual R820T-based RTL-SDR devices primarily because this E4000-based SDR has a much lower current drain on the USB port of the Raspberry Pi 3B+ that it was going to be used with for this tracking task.  This Raspberry Pi runs 24/7 up in the shed and the shed has a tendency to accumulate heat over summer.  Apparently it excels at sensitivity at <500MHz and >1500MHz, and is capable of far higher frequencies, up to approximately 2350MHz.  There is a small gap in frequency capability near 1100MHz.  For about AU$76 delivered, it is a great little unit, the SMA connector was an additional bonus too.  Rather than use the internal Bias-Tee facility with the Mini-Kits LNA that was chosen for the job, an external bias tee was used with a +10VDC wall wart.  This allowed the LNA to be powered up and shut down with a 240V mains programmable timer, set to operate around morning and evening balloon flights.

Duncan chose several of these generic SDR boards cloned from an SDRplay RSP1 design as a general purpose SDR for various projects.  This particular model has been around for a while, sporting a single SMA input, two banks of switches to select different frequency ranges and a USB C connector for power input and data output.  Supplied with a USB-A to USB-C cable and not much else, it really needs some effective shielding prior to use, assuming you find software that will run it.  Don't bother with the SDRplay API or SDRconnect etc... they have locked these clones out.  GNU Radio can acccomodate this device, and so can Gqrx if you're willing to find the patches and add-on software to do so.  Unfortunately for Peter, this device may be unsuitable for SPECTRE, a suite of programs under development for the automated recording, analysis, and visualisation of radio spectrograms.  Perhaps DragonOS_Pi64 or DragonOS_Focal will prove to be the way to go for this project.