HamSci PSWS Grape1

HamSci is a group of hams participating in citizen science projects. You can find out more at www.hamsci.org/ .

One of their projects is a Personal Space Weather Station which "aims to create a small, multi-instrument system that can make ground-based measurements of the space environment. " More info here www.hamsci.org/basic-project/personal-space-weather-station and in an April, 2018 QST article www.hamsci.org/sites/default/files/publications/201804_QST_Silver_PSSW.pdf

Part of that project includes monitoring the ionisphere by accurately observing the Doppler frequency shifts seen while monitoring time stations like WWV. There are both low cost and high performance development tracks in progress. This page covers experiences I had building and using the initial "low cost" Grape1 receiver www.hamsci.org/grape1 This is a development release of the design which, based on experience gained, will be revised, so the Grape1 receiver has a limited useful life.

The basic system includes a Leo Bodner GPS Disiplined Oscillator, The Grape1 receiver, an HF antenna and a Raspberry Pi 4 with a USB audio dongle and software. The receiver is a small PCB with surface mount components that includes RF filters, a mixer and audio filters. The GPSDO is used for a local oscillator. I ordered a set of three boards from oshpark.com/ and parts from Digi-Key.

The receiver build was not difficult except for the RF protection diode package which is vanishingly small. I also destroyed the power indicating LED when it stuck to the soldering iron instead of the PCB. 2 pin headers were added for signal out and power in. I packaged my Grape1 in a 3D printed tray placed in an Altoids tin. Connections are RF in, LO in, DC power and audio out. All connections were choked to cut down common mode RFI . The receiver is powered by an ancient linear transformer wall wart I had laying around. The Pi 4 has heat sinks applied and is in a case with a cooling fan and is powered by the Raspberry Pi "official" wall wart. The wall warts are plugged into a Furman SS6B surge protector and RFI/EMI reducer.

The antenna is a 4' diameter small loop made of .410" diameter coax cable sheath and tuned with an air variable cap to 10 MHz yielding a 1.6:1 SWR. The antenna loop is in the North/South plane so its pattern main lobes are East/West facing WWV in Colorado from my home in NE Ohio. The antenna is 11' from the Pi/Grape1/power supplies and all are in an outbuilding on the opposite side of my house from the ham station and about 90' away. The antenna null also faces my ham antennas and nearby neighbors. My nearest East/West neighbors are more that 500 meters away. I have monitored the Grape1 while transmitting on 30 meters and saw that the receiver was not overloaded and did not loose track of WWV. The GPSDO antenna is also inside the building but the Leo Bodner GPSDO has no problem finding satellites through the wood and shingle roof.

The Raspberry Pi 4 runs custom software available here: github.com/HamSCI/PSWS_Documentation The software includes a modified version of fldigi and several utility python programs for station setup and operation. RealVNC is included and after installing a RealVNC client on your local computer you can monitor and transfer files remotely from the headless Pi.

After your station is running well you can request a node number and send your collected data to HamSci.

To better understand the data collected I programed a python plotting utility that can plot multiple raw data sets from one or more nodes. The code is available here github.com/rkayakr/PSWSmultiPlot

An updated program that plots processed files for one or more nodes, dates and beacons is at github.com/rkayakr/ProcessPlot/releases

Some examples are below:

A bug in the system

I noticed that fldigi was not getting a signal. I assumed that I had knocked off a wire while handling for the magnetometer install. I open the case and found a bug.