kopia lustrzana https://github.com/JamesP6000/PiCW
208 wiersze
8.7 KiB
Plaintext
208 wiersze
8.7 KiB
Plaintext
Raspberry Pi bareback LF/MF/HF/VHF CW (Morse code) transmitter
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Makes a very simple Morse Code transmitter from your RasberryPi by connecting
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GPIO port 4 to Antenna (and LPF). Operates on LF, MF, HF and VHF bands from 0
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to 250 MHz.
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Compatible with the original Raspberry Pi, the Raspberry Pi 2/3, and
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the Pi Zero.
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******
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Installation / update:
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******
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Simple instructions (see BUILD file for more information):
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sudo apt-get install git
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git clone https://github.com/JamesP6000/PiCW.git
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cd PiCW
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make
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Note that compiling takes about 60 seconds on the RPi v1!
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Install to /usr/local/bin:
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sudo make install
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Uninstall:
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sudo make uninstall
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******
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Example usage:
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******
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Brief help screen
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./PiCW --help
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Send the Morse code message "TEST DE N9NNN" on carrier frequency 10.140 MHz
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using the default rate of 20 WPM:
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sudo ./PiCW --freq 10.140e6 TEST DE N9NNN
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Transmit an endless series of dits at 60 WPM. Can be used to measure the
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worst case frequency domain performance of the transmitter.
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sudo ./PiCW --freq 10.140e6 --ditdit --wpm 60
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Transmit a continuous tone at 10.140 MHz
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sudo ./PiCW --freq 10.140e6 --test-tone
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******
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"PiCW --help" output:
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******
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Usage:
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PiCW [options] "text to send in Morse code"
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Options:
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-h --help
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Print out this help screen.
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-f --freq f
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Specify the frequency to be used for the transmission.
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-w --wpm w
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Specify the transmission speed in Words Per Minute (default 20 WPM).
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-p --ppm ppm
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Known PPM correction to 19.2MHz RPi nominal crystal frequency.
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-s --self-calibration
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Call NTP periodically to obtain the PPM error of the crystal (default).
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-n --no-self-cal
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Do not use NTP to correct frequency error of RPi crystal.
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-d --ditdit
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Transmit an endless series of dits. Can be used to measure TX spectrum.
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-t --test-tone
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Continuously transmit a test tone at the requested frequency.
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******
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Radio licensing / RF:
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******
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In order to transmit legally, a HAM Radio License is REQUIRED for running
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this experiment. The output is a square wave so a low pass filter is REQUIRED.
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Connect a low-pass filter (via decoupling C) to GPIO4 (GPCLK0) and a ground
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pin of your Raspberry Pi, then connect an antenna to the LPF. The GPIO4 and
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GND pins are found on header P1 pin 7 and 9 respectively, the pin closest to
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P1 label is pin 1 and its 3rd and 4th neighbour is pin 7 and 9 respectively.
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See this link for pin layout: http://elinux.org/RPi_Low-level_peripherals
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Examples of low-pass filters can be found here:
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http://www.qrp-labs.com/LPF
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http://www.qrp-labs.com/ULPF
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http://www.gqrp.com/harmonic_filters.pdf
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TAPR makes a very nice shield for the Raspberry Pi that is pre-assembled,
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performs the appropriate filtering for the 20m band, and also increases
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the power output to 100mW (+20dBm)! Just connect your antenna and you're
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good-to-go!
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https://www.tapr.org/kits_20M-wspr-pi.html
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The expected power output is 10mW (+10dBm) in a 50 Ohm load. This looks
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neglible, but when connected to a simple dipole antenna this may result in
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reception reports ranging up to several thousands of kilometers.
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As the Raspberry Pi does not attenuate ripple and noise components from the
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5V USB power supply, it is RECOMMENDED to use a regulated supply that has
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sufficient ripple supression. Supply ripple might be seen as mixing products
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centered around the transmit carrier typically at 100/120Hz.
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DO NOT expose GPIO4 to voltages or currents that are above the specified
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Absolute Maximum limits. GPIO4 outputs a digital clock in 3V3 logic, with a
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maximum current of 16mA. As there is no current protection available and a DC
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component of 1.6V, DO NOT short-circuit or place a resistive (dummy) load
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straight on the GPIO4 pin, as it may draw too much current. Instead, use a
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decoupling capacitor to remove DC component when connecting the output to
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dummy loads, transformers, antennas, etc.
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DO NOT expose GPIO4 to electro- static voltages or voltages exceeding the
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0 to 3.3V logic range. Connecting an antenna directly to GPIO4 may damage
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your RPi due to transient voltages such as lightning or static buildup as
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well as RF from other transmitters operating into nearby antennas. Therefore
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it is RECOMMENDED to add some form of isolation, e.g. by using a RF
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transformer, a simple buffer/driver/PA stage, two schottky small signal
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diodes back to back.
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In transmitting Morse code, the CW carrier must be turned on and off.
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To avoid abruptly turning the carrier on and off, the drive strength
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of the GPIO pin used for transmission is gradually increased from 0 to
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16ma with the idea being that this will reduce the frequency spurs created.
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Specifically, the current is increased up to maximum current by following
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the shape of a raised cosine curve.
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Furthermore, a random amount of time domain jitter is added to the turn on
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and turn off ramps to again reduce the spurs created by the turn on/ off
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transients.
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******
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Calibration:
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******
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As of 2017-02, NTP calibration is enabled by default and produces a
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frequency error of about 0.1 PPM after the Pi has temperature stabilized
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and the NTP loop has converged.
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Frequency calibration is HIGHLY recommended to ensure that your
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transmissions lie within the CW band you are targetting.
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NTP calibration:
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NTP automatically tracks and calculates a PPM frequency correction. If your
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Pi is connected to the internet and you are running NTP, you can use the
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--self-calibration option to have PiCW periodically querry NTP for the latest
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frequency correction. Some residual frequency error may still be present
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due to delays in the NTP measurement loop. This method works best if your
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Pi has been on for a long time, the crystal's temperature has stabilized,
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and the NTP control loop has converged.
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AM calibration:
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A practical way to calibrate is to tune the transmitter on the same frequency
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of a medium wave AM broadcast station. Keep tuning until you zero beat (the
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constant audio tone disappears when the transmitter is exactly on the same
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frequency as the broadcast station), and determine the frequency difference
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with the broadcast station. This is the frequency error that can be applied
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for correction while tuning on a WSPR frequency.
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Suppose your local AM radio station is at 780kHz. Use the --test-tone option
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to produce different tones around 780kHz (eg 780100 Hz) until you can
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successfully zero beat the AM station. If the zero beat tone specified on the
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command line is F, calculate the PPM correction required as:
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ppm=(F/780000-1)*1e6 In the future, specify this value as the argument to the
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--ppm option on the command line.
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******
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PWM Peripheral:
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******
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The code uses the RPi PWM peripheral to time the frequency transitions
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of the output clock. This peripheral is also used by the RPi sound system
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and hence any sound events that occur during transmission will
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interfere with CW transmissions. Sound can be permanently disabled
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by editing /etc/modules and commenting out the snd-bcm2835 device.
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******
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Reference documentation:
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******
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http://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
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http://www.scribd.com/doc/127599939/BCM2835-Audio-clocks
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http://www.scribd.com/doc/101830961/GPIO-Pads-Control2
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https://github.com/mgottschlag/vctools/blob/master/vcdb/cm.yaml
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https://www.kernel.org/doc/Documentation/vm/pagemap.txt
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******
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History/Credits:
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******
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Credits go to Oliver Mattos and Oskar Weigl who implemented PiFM based on
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the idea of exploiting RPi DPLL as FM transmitter.
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http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
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Dan MD1CLV combined this effort with WSPR encoding algorithm from F8CHK,
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resulting in WsprryPi a WSPR beacon for LF and MF bands.
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https://github.com/DanAnkers/WsprryPi
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Guido PE1NNZ <pe1nnz@amsat.org> extended this effort with DMA based PWM
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modulation of fractional divider that was part of PiFM, allowing to operate
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the WSPR beacon also on HF and VHF bands. In addition time-synchronisation
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and double amount of power output was implemented.
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https://github.com/threeme3/WsprryPi
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James Peroulas <james@peroulas.com> AB0JP added several command line options,
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a makefile, improved frequency generation precision, and a self calibration
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feature where the code attempts to derrive frequency calibration information
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from an installed NTP deamon.
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https://github.com/JamesP6000/WsprryPi
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Michael Tatarinov for adding a patch to get PPM info directly from the
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kernel.
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James Peroulas <james@peroulas.com> AB0JP created PiCW.
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https://github.com/JamesP6000/PiCW
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Retzler András (HA7ILM) for the massive changes that were required to
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incorporate the mailbox code so that the RPi2 and RPi3 could be supported.
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