siliconchip.com.au Australia’s electronics magazine June 2019 89
use in Australia, the 25mW and 10mW
settings are possible.
Reception sensitivity of the SX1278’s
RF front end is rated at -148dBm,
which corresponds to about 10nV at
the input. As a result, SX1278-based
modules are often described as hav-
ing a reliable communication range
of 3km.
However, this assumes that they are
set for an output power of 100mW,
have a 5dBi gain antenna, a clear line-
of-sight path between them and are
operating at 2400 baud.
In Australia, with a maximum out-
put power of 25mW (taking into ac-
count the antenna gain), this range
drops to around 1.5km. And remember
that this is for a clear line of sight path
with a high-gain antenna and a data
rate of 2400 baud. So in many cases,
you’ll be doing well to get a range of
1km, but that’s still quite useful.
Despite its internal complexity and
multiple functions, the chip is rela-
tively economical in terms of power
consumption. Operating from a 3.3V
DC supply, it draws less than 100mA
in transmit mode (at the 100mW set-
ting), less than 13mA in receive mode
and less than 2mA in standby mode.eByte’s E32-TTL-100 module
As mentioned earlier, the E32-
TTL-100 has a UART/USART serialbefore modulation. GFSK modulation
was the original type of modulation
used in Bluetooth, and is still used
in BR (basic rate) Bluetooth devices.
Fig.1 shows the SX1278’s SPI inter-
face at far right, which allows it to be
fully configured by a microcontroller.
Although two separate UHF front
ends are shown at far left, one for HF
and one for LF, the SX1278 only uses
the LF front end as its specified fre-
quency range is 137-525MHz. It can
be programmed for a spreading fac-
tor of 6-12.
So the main sections of Fig.1 which
are relevant to the SX1278 are the LF
front end at lower left, with its fraction-
al-N PLL (phase-locked loop) driving
the two quadrature (I and Q) mixers,
plus both sections of the fancy modem
at top centre-right.
The modulator section is shown
tinted blue, while the demodulator
section is tinted orange.
The SX1278 can operate at data rates
up to 37.5kb/s, but in the 434MHz
LoRa modules, the maximum recom-
mended rate is 9600 baud, or 2400
baud for maximum reliability.
The transmitter in the SX1278 has
a rated maximum power output of
100mW (+20dBm), but can be pro-
grammed to provide lower output
levels: +17dBm (50mW), +14dBm
(25mW) or +10dBm (10mW). For legalThe RF input/output is via an SMA
connector on one end of the module,
with all of the remaining connections
made via a seven-pin SIL header at the
other end.
While we will focus on using the
E32-TTL-100 module, we’ll still pro-
vide a quick rundown on using the
RA-02.
Since both modules are based on the
SX1278 chip, let’s start by looking at
the chip itself.
Inside the SX1278
Fig.1, the simplified block diagram,
shows what’s inside that compact (6 x
6mm) 28-pin QFN chip. Note that this
diagram covers all four of the different
devices in Semtech’s SX127X range,
not just the SX1278.
The SX1278 is a single-chip UHF
wireless data transceiver combined
with a data modem capable of modu-
lating and demodulating LoRa spread-
spectrum signals.
But it supports other kinds of modu-
lation too, including FSK (frequency-
shift keying), GFSK (Gaussian FSK),
MSK (minimum shift keying), GMSK
(Gaussian MSK) and OOK (on-off key-
ing).
The term ‘Gaussian’ in GFSK and
GMSK signifies that the modulating
data is passed through a Gaussian fil-
ter to make the transitions smoother
Fig.1: block diagram of the SX1276-SX1279 range of LoRa ICs. Even though there’s an upper UHF front end shown in
cyan, the SX1278 only uses the lower band (yellow) from 137-525MHz.