Scientific Computing

Antenna Hungária has broadcast Kossuth Rádió (now also available via internet streaming) on 540 kHz for over 40 years with a two megawatt, 50% efficient transmitter on the 303 meter tower at Transmitter Solt. With the old transmitter, four megawatts of 11 kV utility power resulted in two megawatts of RF on 540 kHz. The new solid-state Nautel NX2000 transmitter commissioned in November 2017 consists of five 400 kW transmitters combined, and “only” 2.2 megawatts input power at 11 kV is needed. Six-inch and twelve-inch RF coaxial hardline pump the RF to the combiner and then the antenna tower. This is the most powerful medium wave transmitter in Europe, and is equal to other most powerful two megawatt medium wave transmitters in the world.

Several one+ megawatt transmitters are shown in this graph.

Models: a groundwave propagation model covering 10 kHz - 30 MHz is described in ITU-R P.368. A very simple example (too inaccurate for planning work) is from ITU grwave. During the 1960s when high altitude nuclear weapons testing was permissible, D-layer absorption increases were thought to be responsible for loss of MW skywave reception for several days over thousands of kilometers. Because ground conductivity is so important, a meaningful MW groundwave model should take into account dynamics of earth conductivity in the coverage area.

Reference:

• MWLIST
• 1958 BBC book on LF and MW groundwave coverage modeling

FGPMMOPA6H GPS manual

• PA6H provides 1 PPS (pin 13) after 3-D Fix at 2.8 V (p. 7, 13)
• 3.3V external antennas may draw up to 28 mA (p.15)
• Power supply: 3.3 V, 25 mA
• NMEA: GGA, GSA, GSV, RMC, VTG over 2.8 V TTL (p. 17)

The PA6H GPS module and Raspberry Pi can make an NTP server. Note that the Raspberry Pi has 3.3 V logic so level shifters may be necessary to/from the 2.8 V GPS IO.

NMEA over UART: the Raspberry Pi UART via PySerial can read NMEA with a program such as NMEAutils. The hardware UART connection is to GPIO pins 14 and 15 on the various Raspberry Pi versions.

Red Pitaya NMEA over UART: starting with the Red Pitaya UART Example in C, one could scoop up the NMEA and extract the current time using a 1PPS driven interrupt. Perhaps use PySerial to access /dev/ttyPS1 to use the Red Pitaya UART from Python. The Red Pitaya UART pinout is to pins 7 and 8 of connector E2.

This would not be for setting the clock accurately like NTP, but rather for determining which second the 1PPS tick occurred at. This technique (with different hardware) was used for the HiST auroral tomography system.

The obsolete Fortran 66 statement pause had various behaviors depending on the operating system and compiler. Fortran pause was used for three different purposes in the Fortran 66 / 77 era:

• (most common use) program waits forever, until the user pressed the Enter key, ignoring typed input.
• wait for user to type text on tty stdin, assigning the typed text to a variable.
• (very old programs) drop to a system shell, allowing any shell command to be used

These can be replaced with unambiguous modern Fortran code.

Wait till Enter: the program waits for the Enter key, ignoring any console input.

use, intrinsic:: iso_fortran_env, only: input_unit

print *, 'Waiting for Enter.'
read(input_unit, *)

The examples below are for Ubuntu, but equivalents may be found for Debian Gentoo Arch Linux and other distros.

File: “Search the content of Packages” in the Ubuntu Package Search, to find which packages provide a file for specific Ubuntu versions. This is important for files that aren’t available in your Ubuntu version.

Example: search for core/dbus/dbus.h shows it’s in libdbus-cpp-dev.

Program: show which versions Fortran open-coarrays is available in. Search source package names open-coarrays

Microsoft Miracast display adapter worked for me for a couple years. Suddenly I couldn’t pair from an Android device. The adapter is configured to use a PIN, and I had the correct PIN, but nothing would work. I had firmware V.2.0.8372 on the Microsoft Miracast adapter.

Use a native Windows laptop, as typical virtual machine software such as VirtualBox doesn’t provide the necessary software links to allow Miracast to work from a Windows guest OS. After a couple tries, I could connect.

1. Disable PIN and restart adapter
2. Enable PIN and restart adapter

Then the Miracast adapter again worked from an Android device as usual.

From a native Windows laptop:

1. Windows Store → Microsoft Wireless Display Adapter
2. connect to the Miracast adapter.
3. Select Firmware Update

ActOnChanged.py program has a few operating modes on files changed in a Git repo since the last git commit

Print list of changed files:

./ActOnChanged.py ~/mydir

Edit previously changed files in gedit:

./ActOnChanged.py ~/mydir gedit

Web browser preview of all changed Jekyll pages:

./ActOnChanged.py ~/mydir --jekyll

Android devices can be used as Bluetooth Low Energy (BLE) beacon receivers, loggers and transmitters with the nRF Connect app. For initial experiments, instead of buying BLE-specific beacon hardware, consider using old Android tablets and phones to setup a beacon network. Laptop computerss, BLE-enabled microcontrollers, and BLE-enabled single-board computers can also transmit and receive BLE beacons. A typical application of such beacons is for indoor / outdoor position estimation and tracking. BLE beaconing adjustments include:

• transmit beacon contents (de facto standard formats)
• BLE Advertisement period
• BLE Transmit power

BLE logging uses the nRF Logger app. to write to a log file beacon RSSI vs. time.

For the Aug 2017 eclipse measurements in South Carolina, despite the fans installed on each Red Pitaya, it was important to keep track of CPU temperature and voltage as each PiRadar node was unattended.

Shell script: monitor Red Pitaya CPU temperature: get_temperature.sh

#!/bin/sh
#
# based on www.kkn.net/~n6tv/xadc.sh
#
# works in Ash (Red Pitaya ecosystem 0.95) and Bash (ecosystem 0.97)

# path to IIO device
XADC_PATH=/sys/bus/iio/devices/iio:device0

# Note: used "cat" to work in Ash instead of the typically recommended Bash "<".

OFF=$(cat $XADC_PATH/in_temp0_offset)
RAW=$(cat $XADC_PATH/in_temp0_raw)
SCL=$(cat $XADC_PATH/in_temp0_scale)

FORMULA="(($OFF+$RAW)*$SCL)/1000.0"
VAL=$(echo "scale=2;${FORMULA}" | bc)
echo "in_temp0 = ${VAL} °C"

Shell script: monitor DC input voltage: get_voltage.sh

#!/bin/sh

# based on www.kkn.net/~n6tv/xadc.sh
#
# works in Ash (Red Pitaya ecosystem 0.95) and Bash (ecosystem 0.97)

# power supply voltages (predefined scaling)
# note that Ash doesn't have "array" so we use "set --"

# path to IIO device
XADC_PATH=/sys/bus/iio/devices/iio:device0

set -- "in_voltage0_vccint" \
           "in_voltage1_vccaux" \
           "in_voltage2_vccbram" \
           "in_voltage3_vccpint" \
           "in_voltage4_vccpaux" \
           "in_voltage5_vccoddr" \
           "in_voltage6_vrefp" \
           "in_voltage7_vrefn"

for voltage do
  RAW=$(cat ${XADC_PATH}/${voltage}_raw)
  SCL=$(cat ${XADC_PATH}/${voltage}_scale)

  FORMULA="(${RAW}*${SCL})/1000.0"
  VAL=$(echo "scale=2;${FORMULA}" | bc)
  echo "${voltage} = ${VAL} V"
done

monitor measures many board & GPIO

Using serial ports from Linux is easy and robust. Serial ports also work in WINE. PuTTY has GUI configuration for serial port. Minicom or screen give command line access to serial port links.

On Linux, add the user to the “dialout” group for non-root access to serial ports (one-time)

adduser $(whoami) dialout

Then logout and login.

List hardware serial ports (motherboard or PCI card):

apt install setserial

setserial -g /dev/ttyS* | grep -v unknown

List the USB-serial adapter ports:

• Linux: ls /dev/ttyUSB*
• macOS: ls /dev/tty.usbserial*

Find a random available local port with this Python snippet.

#!/usr/bin/env python
from socket import socket

with socket() as s:
    s.bind(('',0))
    print(s.getsockname()[1])

From shell, this returns on STDOUT a free port number. There is a slight race condition where between end of this program and start of your shell program, another program could grab this port.

reference