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SiDRADIO: an integrated
using a DVB-T dongle
. . . incorporating a tuned RF preselector, an
up-converter & coverage from DC to daylight
Pt.1: By JIM ROWE
Below: nearly all the parts for the
SiDRADIO are mounted on a single
large PCB. The DVB-T dongle plugs
directly into an internal USB port
and is housed together with the
PCB in a low-profile instrument
case.
18 Silicon Chip
siliconchip.com.au
SDR
LF/MF/HF
ANTENNA
VHF/UHF
ANTENNA
STANDARD A-B
USB CABLE
(SHORT)
9.500400
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
wowowo
FRONT END
UNIT (INCLUDES
DVB-T DONGLE)
11 – 35MHz
SILICON
CHIP
SiDRADIO
3.4 – 11MHz
1.0 – 3.4MHz
LAPTOP (OR DESKTOP) PC
RUNNING SDR# OR
SIMILAR SDR APPLICATION
300 – 990kHz
100 – 320kHz
IN-BAND TUNING
BAND SELECT
RF GAIN
LF–HF POWER
Fig.1: the SiDRADIO has inputs for LF/MF/HF and VHF/UHF antennas and is
connected to a PC running SDR# (or similar) via a standard USB cable.
VHF-UHF
+12.5V
POWER SUPPLY
CIRCUITRY
+3.3V, +5V
LF-HF
INPUT
CON3
5–BAND
PRESELECTOR &
RF AMPLIFIER
S1
+5V
TO PC
USB PORT
LF-HF
SIGNAL
SWITCHING
RELAY
UPCONVERTER
(SHIFTS SIGNAL
FREQUENCIES
UP BY 125MHz)
CON1
DVB-T DONGLE
CON2
VHF-UHF
INPUT
CON4
USB SIGNAL
LEADS
INSIDE THE BOX
Fig.2: block diagram of the SiDRADIO. It includes a 5-band tuned RF preselector and amplifier,
an up-converter and the DVB-T dongle all in one box. The up-converter shifts LF-HF signals up
by 125MHz so that they can be tuned by the DVB-T dongle.
SiDRADIO is a low-cost communications receiver with
coverage from 100kHz to over 2GHz. It is self-contained,
housing a USB DVB-T dongle plus all the circuitry for
an Up-Converter and RF preselector, and is powered
from your PC via the USB cable.
I
F YOU ARE JUST dipping your toe
into the world of radio communications, you won’t want to spend much
money. However, a fully-fledged communications radio is an expensive
acquisition.
Fortunately, software-defined radios
have radically changed the whole communications scene. This has been further shaken up by the fact that cheap
and readily available USB DVB-T
dongles, normally used for watching
digital TV on a personal computer, can
now be configured as communications
radios with a wide range of reception
modes: FM, AM, SSB, CW etc. Not only
siliconchip.com.au
that but the SDR# software provides
fancy features such as spectrum analyser and waterfall displays on your
PC’s screen.
We first introduced this cheap
and cheerful approach to a softwaredesigned radio (SDR) in the May 2013
issue and followed it with a matching
Up-Converter, to enable the DVB-T
dongle to receive frequencies below
about 52MHz, in the June 2013 issue.
Both of these articles have created a
great deal of reader interest.
Inevitably though, readers are now
hankering for extra features such as
band-switching and tuning, gain on
October 2013 19
L6 1mH
+12.5V
L1: 48T 0.3mm ECW WOUND ON BOBBIN OF FERRITE POT CORE (LF-1060);
TAPS AT 17T & 4T
L2: 14T 0.3mm ECW WOUND ON AN 18mm OD x 6mm FERRITE TOROID (LO-1230);
TAP AT 4T.
L3: 6.5T 0.3mm ECW WOUND ON A 7mm LONG FERRITE BALUN CORE (LF-1222);
TAP AT 1.5T
L4: 15T 0.3mm ECW WOUND ON A MINI COIL FORMER WITH SLUG & SHIELD
CAN (LF-1227); TAP AT 4T.
22k
150k
1 µF
100nF
MMC
RF GAIN
VR1
50k
10nF
L5: 26T 0.3mm ECW WOUND ON AN 18mm OD x 6mm FERRITE TOROID (LO-1230)
12mH
100nF
1.3mH
100k
10nF
L1
1.8k
47k
100k
110 µH
L2
LF/MF/HF
INPUT
CON3
1
1
S2a
T1
2
2
3
4
10 µH
L3
S2b
3
100nF
4
G2
27T
27T
D
5
5
G1
TUNING
VC1
10-210pF*
1 µH
L4
VHF/UHF
INPUT
Q1
BF998
10nF
S
100nF
360Ω
100nF
BAND SELECT
CON4
* BOTH SECTIONS IN PARALLEL, TRIMMERS SET TO MINIMUM
SC
2013
SiDRADIO
Fig.3: the circuit diagram of the SiDRADIO. The tuned RF front-end is based on coils L1-L4 & tuning capacitor VC1. Q1
amplifies the tuned RF signal and feeds it via T1 to the up-converter which is based on an SA612AD/01 or SA602AD/01
double-balanced mixer (IC1) and oscillator XO1. IC1 then feeds the antenna input of the DVB-T dongle via relay RLY1.
the frequency bands covered by the
up-converter and ease of operation,
so that you don’t have to juggle input
cables, supply switching and so on. So
we went back to the drawing board.
We wanted to dispense with the
need for a string of small boxes hooked
up to the PC: the DVB-T dongle, the
LF-HF up-converter and either an
active antenna or an RF preamp and
preselector. Plus, you also need two
antennas and a power supply for the
up-converter and the proposed RF
preamp/preselector. This could easily
end up as an untidy mess of boxes and
cables hooked to your PC.
With SiDRADIO (Software Integrated & Defined Radio), we have
come up with what is effectively a
low-cost integrated communications
20 Silicon Chip
receiver. It combines the DVB-T dongle
(which
ever one you want to use) with
the LF-HF Up-Converter we described
in the June issue (including its HF/
VHF signal-switching relay circuit)
and an RF preamp/preselector, with it
all powered from the PC via a single
USB cable.
The 5-band RF preamp and preselector circuit gives improved reception
on the LF-HF bands from 100kHz to
beyond 35MHz.
Integrated SDR concept
Fig.1 shows how SiDRADIO is connected to your computer. To cover all
the available bands, you will need
a VHF/UHF antenna and an LF-HF
antenna and these are both connected
to their respective sockets on the
rear panel. Also on the rear panel is
a USB socket so that you can hook it
up to your laptop or desktop PC. No
other cables are required, so it is very
straightforward to hook it all up and
then listen to the world.
On the front panel is a 5-position
band switch, a thumb-operated knob
for band tuning and a gain control
knob. On the righthand side of the
front panel is a toggle switch which
allows you to switch between the two
antennas via an internal relay – ie,
there’s no need to disconnect antennas. Our earlier Up-Converter design
lacked this switch.
All of the components and circuitry
for SiDRADIO are built on a doublesided PCB measuring 197 x 156mm,
which is housed (along with the donsiliconchip.com.au
L5 470 µH
D1 1N5819
K
LF-HF POWER
4.7Ω
A
CON1
+5V
USB
TO PC
S1
47 µF
TANT
180Ω
22k
7
8
1
+1.25V
5
2.4k
DrC
SwC
Cin-
6
Ips
1 µF
Vcc
MMC
(TYPE B)
A
IC2
MC34063
Ct
λ LED1
3
K
390pF
GND
4
SwE
2
390Ω
CON2
REG1 LP2950-3.3
+3.3V
OUT
1 0 0nF
4
Vdd
1
10nF
XO1
EN FXO-HC536R OUT
-125
L7
390nH
3
3.3pF
GND
2
GND
47 µF
10k
2
InA
10nF
6
OscB
8
Vcc
4
OutA
IC1
SA612AD
OR SA602AD
InB
RLY1
(JRC-23F-05
OR SIMILAR)
K
470pF
1
(TYPE A)
10 µF
220nF
125MHz
10k
USB TO
DVB-T
DONGLE
+5V
IN
A
VHF/UHF
OUTPUT
TO DONGLE
T2
11T
OutB
Gnd
3
D2
1N4004
2T
5
7
BAND
BAND
BAND
BAND
BAND
T1: WOUND ON AN 18mm OD x 6mm FERRITE TOROID T2: WOUND ON A 14mm LONG FERRITE BALUN CORE
(LF-1220); PRIMARY 11T OF 0.3mm ECW,
(LO-1230); PRIMARY & SECONDARY BOTH 27T OF
SECONDARY 2T OF 0.8mm ECW
0.3mm ECW
BF998
LED
D1, D2
A
K
gle) in a low cost ‘low profile’ ABS
instrument case measuring 225 x 165
x 40mm (W x D x H).
Fig.2 is the block diagram of the
SiDRADIO and shows all the circuit
sections, including the USB DVB-T
dongle. Note switch S1 – it switches
power to the circuitry and controls a
relay which selects either the output
signal from the up-converter or the
signal from the VHF-UHF antenna.
The selected signal is fed to the USB
dongle for processing and its output is
fed via the USB cable to the computer.
Note that the USB cable also feeds
power to the circuitry.
Circuit details
The full circuit diagram of our
SiDRADIO is shown in Fig.3 and if
siliconchip.com.au
G2(3)
K
A
G1(4)
GND
D(2)
S(1)
IN
8
100kHz – 320kHz
300kHz – 1.0MHz
1.0MHz – 3.4MHz
3.4MHz – 11MHz
11MHz – 35MHz
XO1
SA612AD,
SA602AD
LP2950
1:
2:
3:
4:
5:
4
3
4
1
1
OUT
(TP)
2
Table 1: Common DVB-T Dongle Tuner Chips & Their Frequency Ranges
Tuner Chip
Elonics E4000
Frequency Range
DVB-T dongle model in which chip is found
52 – 2200MHz* EzCAP EzTV668 DVB-T/FM/DAB, many current 'no name' devices
Rafael Micro R820T
24 – 1766MHz
? (not known – but may be in many future dongles)
Fitipower FC0013
22 – 1100MHz
EzCAP EzTV645 DVB-T/FM/DAB, Kaiser Baas KBA010008 TV Stick
Fitipower FC0012
22 – 948MHz
Many of the earlier DVB-T dongles
* With a gap from 1100MHz to 1250MHz (approx)
you are familiar with the previous
articles in this series, you’ll see that it
incorporates a good deal of the circuit
of the HF Up-Converter published in
June 2013. The only real difference
is that instead of the Up-Converter’s
input transformer T1 being connected
directly to the LF-HF antenna input as
before, it’s now fed from the output of
the RF preamp and preselector section.
This is the circuitry on the lefthand
NOTE: Elonics may have ceased manufacture
side of Fig.3 and based around Q1, a
BF998 dual-gate VHF depletion-mode
MOSFET.
Q1 is configured as a standard
common-source RF amplifier, with
the incoming RF signals fed to gate
G1 and the transistor’s gain varied by
adjusting the DC bias voltage applied
to gate G2, using 50kΩ pot VR1. The
output signal appears at Q1’s drain,
and is fed directly to the primary of T1.
October 2013 21
input to the input tap on each coil,
while S2b connects tuning capacitor
VC1 and the preamp input to the ‘top’
of each coil. Note that the ‘Q’ of each
coil is relatively modest, so the tuning
of VC1 is fairly broad rather than sharp
and critical. This is especially the case
with coil L1.
Up-converter operation
DVB-T tuner dongles can be purchased online quite cheaply. These three
units all feature a 75-ohm Belling-Lee antenna socket but many other
dongles come with a much smaller MCX connector.
Q1 therefore acts as an RF preamplifier, with VR1 able to adjust its gain
from virtually zero up to approximately +20dB. It may seem strange to have
a preamp whose gain can be reduced
down to zero but having the gain variable over a wide range is essential to
reduce overloading and cross-modulation from very strong signals.
Because Q1 performs best in this
kind of circuit with a +12V DC supply, we are using a DC-DC step-up
converter to derive this +12V from
the +5V USB supply fed in via CON1.
It’s basically a simple boost converter
using IC2, an MC34063, together with
inductor L5 and Schottky diode D1.
The output of the converter is about
+12.5V (12.2-13.2V range), as measured
across the 47µF tantalum capacitor.
The DC-DC converter operates at between 50kHz to 60kHz and as a result
its output voltage carries a significant
amount of ripple at these frequencies. To minimise interference to the
RF preamp due to harmonics of this
ripple (especially on the lowest 100320kHz band), the converter’s output
is filtered using RF choke L6 (1mH)
and its accompanying 1µF capacitor.
These form a low-pass LC filter with
a corner frequency of around 5kHz.
Shielding
Also critical to the circuit’s performance is the shielding we have had
to provide between the converter’s
circuitry (especially L5) and the RF
preamp and preselector circuitry. We
will discuss this shielding later.
The 5-position 2-pole switch (S2a/
S2b), coils L1-L4 and tuning capacitor
VC1 form the preselector section of the
circuit. This is connected between LFHF antenna input connector CON3 and
the preamplifier input. Coils L1-L4 are
used to cover each of the five bands,
with L1 tapped so that it can be used
to cover both of the lower bands. Tuning within each band is then carried
out using VC1.
Switch S2a connects the antenna
Fig.4: this scope
grab shows the
125MHz signal
from the crystal
oscillator. This was
measured using a
400MHz probe and
a 350MHz scope,
so many of the
upper harmonics
have been heavily
attenuated. Even so,
it can be seen that
the waveform is
far from sinusoidal
and that’s why it’s
followed by an LC
filter to clean it
up and so reduce
spurious responses.
22 Silicon Chip
Although we discussed the operation of the up-converter circuit in July
2013, we are also providing a summary here for the benefit of those who
didn’t see the earlier article. The actual
frequency conversion is performed
by IC1, which is an SA612AD or its
close relative the SA602AD. Both are
double-balanced mixer devices designed specifically for this kind of use.
The LF-HF signals to be up-converted
enter the circuit from the RF preamp
via matching transformer T1, before
being fed into the balanced inputs
(pins 1 & 2) of IC1.
The 125MHz signal used to ‘shift’
the input signals up in frequency is
generated by crystal oscillator module
XO1, a very small HCMOS SMD device which produces a 125MHz clock
signal at its pin 3 output. The output
voltage at this pin is 2.65V peak-topeak, which is rather too high for linear
operation of the mixer. In addition,
it’s essentially a square wave, rich in
harmonics of 125MHz as well as the
fundamental. You can see its output in
the scope grab shown in Fig.4.
As a result, this ‘squarish’ 125MHz
signal is fed through a low-pass filter
formed by a 390nH inductor and 3.3pF
capacitor, to filter out most of the
harmonics. These would otherwise
contribute to spurious signals via
cross-modulation in the mixer. Then
we reduce the filtered 125MHz signal
down to a more suitable level for the
mixer, via a voltage divider consisting
of two 10kΩ resistors.
The signal is then fed into the oscillator input (pin 6) of IC1 via a 470pF
coupling capacitor.
Inside the mixer, the balanced input
signals at pins 1 & 2 are mixed with
the 125MHz oscillator signal at pin
6. The resulting mixing products appear in balanced form at the outputs
(pins 4 & 5).
Because IC1 is a double-balanced
mixer based on a Gilbert cell, the
outputs contain very little of the
original input signal frequencies Fin
or the oscillator signal frequency Fosc
siliconchip.com.au
(125MHz). Mainly they contain the
‘sum’ and ‘difference’ products, ie:
Sum product = (Fosc + Fin)
Difference product = (Fosc - Fin)
It’s the sum product that we want.
Although the difference product is also
present in the outputs, the signals it
contains are in a different tuning range
so they can be ignored.
The balanced output signals from
the mixer are passed through a second
matching transformer, T2. As well as
stepping them down in impedance
level (1500Ω:75Ω), T2 also converts
them into unbalanced form to provide
better matching to the input of the
DVB-T dongle.
The output signals from T2 are not
taken directly to the dongle input
but instead to the normally open
contact of relay RLY1. It’s the moving common contact of RLY1 which
connects to the dongle and since
the actuator coil of RLY1 is driven
by the +5V supply line when switch
S1 is closed, this means that the upconverter’s output is only connected
to the dongle when power is applied
via S1. This mode is indicated by LED1
being lit.
When S1 is switched off and +5V
power is not applied, the moving
contact of RLY1 connects to the normally closed contact and this connects
directly to the converter’s VHF/UHF
input connector CON4 at lower left.
So when S1 is turned off to remove
power from the LF-HF front-end circuitry, the input of the DVB-T dongle
is connected directly to the VHF/UHF
antenna, as noted above in the brief
discussion of Fig.2.
IC1 and RLY1 operate directly from
the nominal +5V USB rail, with diode D2 used to absorb any back-EMF
spikes which may be generated by the
coil of RLY1 when power is removed.
Crystal oscillator module XO1 operates from +3.3V and this is derived
by REG1, an LP2950-3.3 LDO (low
drop-out) device in a TO-92 package.
That’s about it, apart from mentioning that the DVB-T dongle is always
connected to the USB port of your PC
regardless of the position of S1. That’s
because USB connectors CON1 and
CON2 are linked together. This means
that providing the USB cable remains
plugged into CON1 and the PC’s port,
the dongle is always powered up and
operating.
So, effectively, S1 acts as a bandsiliconchip.com.au
The SDR# Application & Its Features
SDR# is an easy-to-use software application designed to turn almost any PC
into a powerful SDR (software defined radio), using either a DVB-T dongle (the
hardware “front end”) or other devices. Here are some of its salient features:
(1) RF performance, frequency accuracy: the RF performance basically depends
on the chips used in the DVB-T dongle used with SDR#. A typical dongle fitted
with the Elonics E4000 tuner chip can tune from 52-1100MHz and 1250-2200MHz,
with a sensitivity of approximately 1.5µV for 12dB of quieting at frequencies up to
about 180MHz, rising to about 20µV for the same degree of quieting at 990MHz.
The SDR# software used with the dongle provides a “Frequency Correction”
feature, whereby you can correct for any frequency error in the DVB-T dongle. In
addition, there is a “Frequency Shift” feature, allowing you to display the correct
frequencies even when you have an up-converter connected ahead of the dongle.
(2) Demodulation modes: AM (amplitude modulation), NFM (narrow frequency
modulation), WFM (wide frequency modulation), LSB (lower sideband), USB
(upper sideband), DSB (double sideband), CW-L (carrier wave with BFO on low
side) and CW-U (carrier wave with BFO on high side).
In all these modes, the RF filter bandwidth can be adjusted over a wide range,
while the filter type can be selected from a range of five (Hamming, Blackman,
Blackman-Harris, Hann-Poisson or Youssef). The filter order can also be selected
over a wide range. In both CW modes, the frequency separation of the software
BFO can also be adjusted. There is adjustable squelch and also both linear and
“hang” AGC.
(3) FFT spectrum display and/or Waterfall spectrum/time display: the FFT
spectrum display and Waterfall display can be selected either separately or together.
The windowing function used can be selected from six choices: None, Hamming,
Blackman, Blackman-Harris, Hamm-Poisson or Youssef, and the display resolution
can be adjusted over a wide range by changing the block size from 512 to 4,194,304,
in powers of two, with the higher resolutions requiring greater processing overhead.
Good results can be achieved with the default resolution of 4096, which was
used for the screen grab shown below.
Fig.5: SDR# spectrum and waterfall displays for a 702kHz AM signal. Note
that a frequency shift of 125MHz has been entered (at top right) so that the
correct tuned frequency is displayed.
October 2013 23
3
2
1
A
LED1
K
D1
L5
5819
26T
TPG1
10nF
47k
TPG4
1 µF
TUNING
100nF
Q1
BF998
S
G1
D
100nF
VC1
100nF
100nF
G2
100nF
27T
T1
IC1
SA612A
coded 06109131 and measuring 197
x 156mm. This has a cut-out area at
the righthand end to provide space for
the DVB-T dongle and its input connector, in order to make an integrated
assembly.
As shown in the photos, the PCB/
DVB-T dongle assembly fits neatly into
the low-profile ABS instrument case.
1
2
3
4
5
TPG2
S2
8
ROTOR
B
7
All the parts except for bandswitch
S2 and the VHF-UHF input connector
(CON4) are mounted on a large PCB
4T TAP
GND
Construction
BAND SELECT
ROTOR
A
11
10
9
GND
4T TAP
L4 1.0 µH
1.5T TAP
15T
L3
14T
6.5T
GND
GND
L1
L2
4T TAP
48T
17T TAP
10nF
10nF
TPG3
1
27T
11T
(SA602A) 1
10k
470pF
125MHz
3
XO1
3.3pF
4
2
100k
390nH
select switch, with the dongle receiving LF-HF signals when S1 is in the
on position and VHF/UHF signals
when it is off.
24 Silicon Chip
VR1 50k LIN
LF-HF GAIN
TANT
47 µF
+
L6
T2
TP 12V
VERTICAL
SHIELD
PLATE
1mH
GND
2T
10 µF
+
LP2950
-3.3
220nF
REG1
+
150k
10nF
1.8k
47 µF
SHORT LENGTH
OF 75 Ω COAXIAL
CABLE (RG6)
RLY1
COMMON
COIL
VHF/UHF
OUTPUT
(TO DONGLE)
D2
10k
1 0 0nF
390pF
1 µF
2
1
2.4k
4.7Ω
3
4
JRC-23F-05
RO
F DN
E T N ORF F H
HF FRONT
END
FOR
DESA B EBASED
L G N OD T- BVD
DVB-T DONGLE
OIDAR DE
NIFED ERRADIO
AWTF OS
SOFTWARE
DEFINED
100k
360Ω
10nF
CON1
4004
1
3190160
06109131
3
10
2 C
C
2013
22k
180Ω
CON3
LF-HF INPUT
IC2
CON4
VHF-UHF INPUT
MC34063
NC
22k
USB IN
390Ω
NO
Fig.6: the parts layout & wiring diagram. Start with the SMD parts and make sure all polarised parts are correctly orientated.
LF/HF POWER
4
S1
1
DVB-T
DONGLE
3
2
USB OUT
CON2
4
Rotary bandswitch S2 mounts directly
on the lefthand end of the front panel,
while the VHF-UHF input connector
(CON4) is mounted on the rear panel
with its ‘rear end’ protruding into a
second (small) cut-out in the PCB.
Fig.6 shows the parts layout on the
PCB. There are eight SMD components
in all: IC1 (SA612A), crystal oscillator
siliconchip.com.au
This view shows the completed PCB inside the case, together with a DVB-T dongle. Note that a metal shield is fitted to
the PCB, while horizontal shields are fitted to the top & bottom of the case. These shields are described next month.
module XO1, the 390nH inductor,
a 3.3pF capacitor, a 10nF capacitor
(alongside XO1), the two 10kΩ resistors
and transistor Q1 (BF998). These parts
should be installed first, starting with
the five passive components and then
Q1, XO1 & IC1.
You will need a fine-tipped soldering iron and a magnifier (preferably a
magnifying lamp) to solder the SMD
parts in. The trick is to carefully position each part on the PCB and solder
just one lead to begin with, then check
that the device is correctly aligned
before soldering the remaining leads.
If it’s not correctly located, it’s just a
matter of re-melting the solder on the
first lead and nudging the device into
position.
Don’t worry if you get solder bridges
between IC1’s pins when soldering it
into position. These bridges can easily
be removed using solder wick.
By the way, there are actually two
siliconchip.com.au
versions of the BF998 MOSFET, both in
the SOT-143 SMD 4-pin package – the
standard BF998 and the BF998R with
transposed (reversed) pin connections.
Make sure you are supplied with the
former and not the latter, because the
PCB has been designed to suit the
standard version and won’t take the
‘R’ version. If you source the BF998
device from element14, it has the part
number 1081286.
Both the SA612AD and the SA602AD
mixer devices are in an SOIC-8 package and are pin compatible, so you
can use either as IC1. They are made
by NXP (formerly Philips) and are
available from a number of suppliers
including element14. Whichever one
you use, just make sure you fit it with
the orientation shown in Fig.6 – ie,
with its bevelled long edge towards
transformer T1.
Crystal oscillator module XO1 has a
footprint of just 4 x 3mm. This is a Fox
‘XPRESSO’ FXO-HC536-125 device,
also available from element14.
Its orientation is also critical; it must
go in with pin 1 (indicated by a tiny
arrow or ‘foxhead’ symbol etched into
one corner of the top sealing plate) at
lower left as viewed in Fig.6 (you may
need a good magnifying glass to locate
that symbol).
Once these are in, install the leaded
passive components, starting with
the resistors and moving on to the
capacitors and RF choke L6. Diodes
D1 & D2 can then go in, making
sure that you fit the correct diode in
each position and with the correct
orientation
Follow with 3.3V regulator REG1,
then fit the MC34063 DC-DC converter
controller (IC2). Again, make sure that
these parts are fitted the right way
around.
Power switch S1 is next, after which
you can fit the USB input and output
October 2013 25
replaced with M2.5 x 6mm screws,
to cope with the additional length
required due to the spacers.
Make sure that VC1’s three connection lugs at the rear are fed through
their matching pads on the PCB when
it is installed. Once VC1 is secured in
position, these leads are then soldered
to the pads on both sides of the PCB.
The tuning knob can then be fastened
to the shaft using one of the supplied
M2.5 x 4mm screws.
Main Features & Specifications
A compact ‘RF front end’ for a software defined radio using a laptop or desktop PC. It can
incorporate virtually any of the DVB-T dongles used for SDR and couples the dongle to an
up-converter for LF-HF reception, the latter effectively shifting LF-HF radio signals up by
125MHz into the VHF spectrum.
The front end also includes a signal switching relay so when power is not applied to the
LF-HF preselector and up-converter circuitry, the dongle’s VHF-UHF signal input is switched
directly to the VHF/UHF input (this avoids the need for cable swapping). All power for both
the dongle and the front-end circuitry is derived from the USB port of the PC.
VHF/UHF input impedance: 75Ω unbalanced.
Coils & transformers
Up-converter section conversion gain: approximately +10dB ±2dB over the input range
100kHz - 35MHz (corresponding output range = 125.1MHz - 180MHz).
The next step is to wind transformers T1 & T2 and also coils L1-L5. We’ll
deal with transformer T1 and coils L2
& L5 first, since they are all wound on
identical toroidal ferrite cores, each
with an outside diameter of 18mm and
a depth of 6mm (eg, Jaycar LO-1230
or similar).
• Transformer T1’s primary and secondary windings both consist of 27
turns of 0.3mm ECW (enamelled
copper wire) wound closely on opposite sides of the toroid (they can be
temporarily secured with tape). When
both windings have been made, trim
the leads to about 10mm and strip off
5mm of enamel from each end.
The toroid assembly can then be
mounted on the PCB and secured in
place using two small Nylon cable ties
as shown in Fig.6. After that, it’s just
a matter of soldering its four leads to
the relevant pads on the PCB.
• Coil L2 consists of a single winding
of 14 turns with a tap connection at
four turns, again using 0.3mm ECW.
After winding the first four turns, bring
the wire straight out from the toroid,
then double it back after about 12mm
to form the tap connection and wind
on the remaining 10 turns in the same
direction as the first four.
LF-HF input impedance: 50Ω unbalanced.
Preselector bands: Band 1 = 100-320kHz; Band 2 = 300kHz-1MHz; Band 3 = 1-3.4MHz;
Band 4 = 3.4-11MHz; Band 5 = 11-35MHz
RF gain: variable from zero to about +20dB, over the range 100kHz - 35MHz.
Typical effective LF-HF sensitivity: Band 1 = 20-50μV; Band 2 = 18-50μV; Band 3 =
5-12μV; Band 4 = 1.5-4μV; Band 5 = 1-2μV
VHF/UHF output impedance: 75Ω unbalanced.
Power supply: 5V DC from computer USB port.
Current drain for VHF-UHF reception (ie, dongle only): less than 70mA.
Current drain for LF-HF reception: less than 220mA.
connectors (CON1 & CON2), the LFHF input connector (CON3) and relay
RLY1. Note that RLY1 is again a very
small component, measuring just 12 x
7 x 10mm (L x W x H). A JRC-23F-05
relay from Futurlec was fitted to the
prototype.
Next you can fit the PCB terminal
pins. There are 19 of these, 12 of which
are located to the rear of S2 and one
(TPG2) to the left of S2. Another TPG
pin is located at upper left near CON3,
while two further pins are located at
centre right to terminate the RF output
cable to the DVB-T dongle.
The remaining three pins are at
lower centre of the PCB, two to the
left of inductor L6 and one to the left
of potentiometer VR1.
Fitting VC1
The next step is to fit tuning capacitor VC1. This must be spaced up from
the PCB by 3.5mm, so that the tuning
knob just clears the bottom of the
case when the PCB is later fitted into
it. Fig.7 shows the mounting details.
As can be seen, an M3 nut and a
small flat washer is used as a spacer
on either side. In addition, the M2.5
x 4mm mounting screws supplied
with the tuning capacitor have to be
MINI TUNING CAPACITOR
(CONNECTION PINS AT REAR)
M3 NUTS AND
FLAT WASHERS
USED AS SPACERS
M2.5 x 6mm
LONG SCREWS
PCB
TUNING
KNOB/DISC
(VIEW FROM FRONT)
Fig.7: this diagram shows the mounting
details for tuning capacitor VC1. It must be
stood off the PCB by 3.5mm using M3 nuts
and flat washers as spacers, so that its tuning
wheel clears the bottom the case.
26 Silicon Chip
Fig.8: the winding
details for coil L4.
It’s wound using
0.3mm ECW on
a small RF coil
former, with a tap
after four turns at
position ‘A’. Don’t
forget to fit the
ferrite slug.
PLASTIC COIL
FORMER & BASE
FERRITE
SLUG
1
2
1
2
A
2
2
1
2
15T
(FINISH)
4T
TAP
2
TOP
VIEW
1
1
1
GND
GND
1
2
3
SOLDER WIRE
END TO PIN 1,
WIND 4 TURNS
AT BOTTOM
OF FORMER
MAKE LOOP IN WIRE,
BEND DOWN THROUGH
SLOT 'A' THEN WIND
ON 11 MORE TURNS
(IN SAME DIRECTION)
AFTER WINDING ON 11
MORE TURNS, SOLDER
WIRE END TO PIN 2.
ALSO SCREW SLUG
INTO CORE.
WINDING DETAILS FOR COIL L4
siliconchip.com.au
Software Is Crucial
The software needed to configure
a DVB-T dongle and PC combination as an SDR consists of two main
components: (1) a driver which allows
the PC to communicate via the USB
port with the Realtek RTL2832U (or
similar) demodulator chip inside the
dongle; and (2) application software
to allow the PC to perform all the
functions of an SDR in company with
the SiDRADIO and its DVB-T dongle.
The driver must be installed first.
The most popular driver for a DVB-T
dongle with an RTL2832U demodulator chip (when used as an SDR)
is the “RTLSDR” driver (nearly all
dongles use the RTL2832U). The
website at www.rtlsdr.org provides
lots of information on this.
Once the driver has been installed,
the application software can be installed. The most popular application
software is SDR#, available from
www.SDRSharp.com
The article on Software Defined
Radio in the May 2013 issue of SILICON
CHIP has all the details on installing
the driver and application software.
That done, trim the start and finish
ends to about 10mm and strip 6mm
of enamel from each end and from the
tap loop. The coil can then be fitted to
the PCB, secured with Nylon cable ties
and the leads soldered.
• Coil L5 can be tackled next. It simply consists of 26 turns of 0.3mm ECW,
with no taps or other complications.
As before, it’s secured to the top of the
PCB using two small cable ties.
• RF output transformer T2 is wound
on a 14mm-long ferrite balun core
(Jaycar LF-1220 or similar), with the
winding wire passed up through one
hole in the balun core and then back
down through the other hole, and so on.
The secondary consists of just two
turns of 0.8mm ECW and should be
wound first. Then you can wind the
primary, which consists of 11 turns
of 0.25mm ECW. Note that the leads
of the two windings emerge from opposite ends of the balun.
When you have finished both windings, trim the free wire ends to about
10mm and strip the enamel from each
end. The completed balun can then be
mounted on the PCB and its four wire
leads soldered to their respective pads.
Make sure that the balun is orientated
with its 11-turn primary winding to
the left and solder these wires on both
sides of the PCB.
• Coil L3 is wound on one of the
smaller 6mm-long ferrite balun cores
(Jaycar LF-1222 or similar). In this
case, you need to wind on 6.5 turns
of 0.3mm ECW with a ‘loop tap’ made
after 1.5 turns from the start (ie, from
the GND connection).
It’s just a matter of winding on the
first 1.5 turns, then bringing the wire
out and doubling it back after about
12mm to form the tap, then winding
on the remaining five turns – see Fig.6.
• Coil L4 (band 5) is close-wound on
a small RF coil former that’s fitted with
a ferrite tuning slug and housed in a
shield can (Jaycar LF-1227 or similar).
Although this coil only has 15 turns of
0.3mm ECW with a loop tap, it’s a bit
fiddly to wind because of the former’s
small size and because the former has
only two termination pins.
Fig.8 shows the winding details for
L4. The ‘loop tap’ is formed just after
Table 1: Resistor Colour Codes
o
o
o
o
o
o
o
o
o
o
o
o
siliconchip.com.au
No.
1
2
1
2
2
1
1
1
1
1
1
Value
150kΩ
100kΩ
47kΩ
22kΩ
10kΩ
2.4kΩ
1.8kΩ
390Ω
360Ω
180Ω
4.7Ω
4-Band Code (1%)
brown green yellow brown
brown black yellow brown
yellow violet orange brown
red red orange brown
brown black orange brown
red yellow red brown
brown grey red brown
orange white brown brown
orange blue brown brown
brown grey brown brown
yellow violet gold brown
four turns from the start/GND end (pin
1) and is fed down through one of the
small slots (A) in the former’s base, so
that it can subsequently be fed through
its matching hole in the PCB. Again,
make this ‘loop tap’ about 12mm long,
then wind on the remaining 11 turns
and terminate the wire on pin 2.
That done, screw the supplied ferrite slug into the former, along with the
small piece of rubber thread supplied
to act as a ‘hold tight’. You should
then scrape the insulating enamel
from the ‘tap loop’ so that it’s ready
for soldering.
The completed coil assembly can
now be mounted on the PCB (just
below coil L3). Orientate it as shown
on Fig.6, so that the two pins and
the ‘tap loop’ each go through their
matching PCB holes (ie, pin 1 GND at
bottom right, 4T tap at top). Once it’s
in place, solder the three connections
underneath the PCB, making sure that
you get a good solder joint to both of
the tap loop wires.
The next step is to gently screw
down the ferrite slug inside L4 using
a Nylon alignment tool until it just
touches the surface of the PCB. That
done, slip the metal shield can over
the completed coil former, until its two
attachment lugs pass down through
the holes provided on each side. These
Capacitor Codes
Value
1µF
220nF
100nF
10nF
470pF
390pF
3.3pF
µF Value
1µF
0.22µF
0.1µF
0.01µF
NA
NA
NA
IEC Code EIA Code
1u0
105
220n
224
100n
104
10n
103
470p
471
390p
391
3p3
3.3
5-Band Code (1%)
brown green black orange brown
brown black black orange brown
yellow violet black red brown
red red black red brown
brown black black red brown
red yellow black brown brown
brown grey black brown brown
orange white black black brown
orange blue black black brown
brown grey black black brown
yellow violet black silver brown
October 2013 27
Parts List For SiDRADIO
1 low profile ABS instrument case,
225 x 165 x 40mm (Jaycar HB5972 or similar)
1 double-sided PCB, code
06109131, 197 x 156mm
1 set of front & rear PCB panels,
code 06109132 & 06109133
(200 x 30mm)
1 DVB-T dongle (using an RTL2832U decoder chip and either
the R820T, E4000 or FC0013
tuner chips)
1 short length of 75Ω coaxial
cable, with plug to suit RF input
of dongle
1 HCMOS 3.3V crystal oscillator
module, 125MHz (Fox Electron
ics FXO-HC536-125 or similar,
element14 2058072) (XO1)
1 SPDT 5V mini DIP relay, JRC23F-05 or similar (Futurlec)
(RLY1)
1 SPDT PCB-mount vertical acting
toggle switch (S1) (Altronics
S1320)
1 2-pole 5/6-position rotary switch
(S2)
1 USB type B socket, horizontal
PCB-mount (CON1)
1 USB type A socket, horizontal
PCB-mount (CON2)
1 BNC socket, PCB mount (CON3)
1 PAL (Belling-Lee) socket, panelmount (CON4)
2 instrument knobs, 20mm diameter x 18mm deep (Jaycar HK7786 or similar)
3 toroidal ferrite cores, 18mm
diameter x 6mm deep (Jaycar
LO-1230 or similar)
1 6mm-long ferrite balun core (Jaycar LF-1222 or similar)
1 14mm-long ferrite balun core
(Jaycar LF-1220 or similar)
8 small Nylon cable ties
1 mini RF coil former with slug and
shield can (Jaycar LF-1227 or
similar)
1 pair of ferrite pot core halves
with bobbin (Jaycar LF-1060 +
LF1062)
1 50kΩ linear pot, 16mm (VR1)
1 miniature PCB-mount tuning
capacitor with knob & mounting
screws (VC1) (Jaycar RV-5728
or similar)
1 M3 x 25mm Nylon machine screw
1 M3 Nylon nut
2 M3 flat Nylon washers
28 Silicon Chip
M3 NYLON
NUT
19 PCB pins, 1mm diameter
1 1mH axial RF choke/inductor (L6)
1 390nH SMD inductor, 0805 (L7)
2 M2.5 x 6mm machine screws
10 6mm-long No.4 self-tapping
screws
1 M3 x 6mm machine screw
1 M3 spring lockwasher
3 M3 nuts
2 M3 flat washers
1 90 x 36 x 0.8mm aluminium sheet
or tinplate (to make vertical
shield)
1 rectangular piece of blank PCB,
195 x 150mm (for top horizontal
shield)
1 196 x 134 x 0.25mm copper foil
or tinplate (for bottom horizontal
shield)
1 200mm-length 0.25mm-dia, ECW
1 1m-length 0.3mm-dia. ECW
1 100mm-length 0.8mm-dia. ECW
Tinned copper wire, hook-up wire,
etc
Semiconductors
1 SA612AD/01 or SA602AD/01
double balanced mixer (IC1) (element14 2212081 or 2212077)
1 MC34063 DC-DC converter (IC2)
1 BF998 dual-gate VHF MOSFET
(Q1) (element14 1081286)
1 LP2950-3.3 or LM2936-3.3 LDO
regulator (REG1)
1 5mm green LED (LED1)
1 1N5819 Schottky diode (D1)
1 1N4004 silicon diode (D2)
Capacitors
1 47µF 10V RB electrolytic
1 47µF 16V tantalum
1 10µF 16V RB electrolytic
2 1µF MMC
1 220nF MMC
5 100nF MMC
5 10nF MMC
1 10nF SMD ceramic (1206)
1 470pF disc ceramic
1 390pF disc ceramic
1 3.3pF C0G/NP0 SMD ceramic
(1206)
Resistors (0.25W, 1%)
1 150kΩ
2 100kΩ
1 47kΩ
2 22kΩ
2 10kΩ SMD (0805)
1 2.4kΩ
1 1.8kΩ
1 390Ω
1 360Ω
1 180Ω
1 4.7Ω 0.5W
FERRITE
POT CORE
HALVES
NYLON
FLAT
WASHER
PCB
M3 x 25mm
NYLON SCREW
NYLON FLAT
WASHER
(TOP VIEW)
(START)
GND
17.5T
TAP
4T
TAP
48T
(FINISH)
Fig.9: coil L1 is wound on the
bobbin of a 2-part ferrite pot core
(see text) and secured to the PCB
using an M3 x 25mm Nylon screw,
washers and nut.
are then soldered to their pads on the
underside of the PCB to secure the
can in place.
Winding coil L1
The remaining coil to be wound is
L1 – see Fig.9. It’s wound on the bobbin of a 2-section ferrite pot core assembly measuring 25mm in diameter
and 16.5mm high (Jaycar LF-1060 +
LF1062).
This coil is wound in a conventional
fashion directly on the bobbin and
consists of 48 turns of 0.3mm ECW
with two tapping loops. The winding
procedure is as follows.
First, anchor the ‘start’ end of the
wire to one side of the bobbin using
cellulose tape. That done, close-wind
four turns onto the bobbin, then bring
out a loop of wire to form the antenna
‘tap’ via the same slot in the bobbin’s
side that was used for the ‘start’ lead.
Anchor this loop tap to the side of
the bobbin with another small piece
of cellulose tape, then close-wind on
13.5 more turns in the same direction
as the first four turns.
After winding on these extra turns,
bring out another tap loop through the
slot in the opposite side of the bobbin
(ie, opposite the ‘start’ and ‘4T tap’
wires). Anchor this loop to the outside
of the bobbin using cellulose tape, then
siliconchip.com.au
Performance Limitations
While the combination of a DVB-T dongle with an up-converter and an HF
preamp and preselector – as provided by the SiDRADIO – can provide many
of the operating features of a high-performance communications receiver, it’s
unrealistic to expect exactly the same performance. The high cost of communications receivers is the price you pay for superb sensitivity and selectivity, FM
quieting, excellent image rejection and so on. You are not going to get that sort
of performance from a set-up costing a great deal less.
Apart from anything else, most DVB-T dongles are in a plastic case that provides no shielding against the ingress of strong VHF signals like those from FM
stations and DAB+ stations – or from the PC you’re using with the SDR front
end. So even though we have taken a great deal of care to provide shielding for
both the dongle and the rest of the front end circuitry, you’re still likely to find
spurious ‘breakthrough’ signals in that part of the VHF spectrum into which the
up-converter shifts the incoming HF signals. Having said that, the shielding does
significantly reduce breakthrough compared to an unshielded dongle.
Another reason why you’ll tend to find spurious signals is that the simple
input tuning circuitry of the preselector section is inevitably rather modest in
terms of selectivity. So although the new unit does provide improved rejection
of interfering signals compared with the June 2013 “LF-HF To VHF Up-Converter”
with its broadband input, it’s still not in the same league as a high-performance
HF communications receiver.
In spite of that, it’s surprising what results you can get out of this new all-inone SDR interface, particularly if you team it up with a long-wire HF antenna or
an active indoor HF loop antenna with its own low-Q tuning circuit.
wind on a further 13 turns to fill this
first winding layer.
Next, apply a narrow strip (9-10mm
wide) of cellulose tape over this layer
to hold it all in place, then continue
winding in the same direction to produce a second layer of 18 turns.
When the last turn has been wound
on, bring the wire end out through the
same bobbin slot as the ‘17.5T tapping loop’ and cut it off about 10mm
from the bobbin. This lead becomes
the 48-turn ‘top’ of coil L1. Another
narrow strip of cellulose tape is then
placed over the second layer to hold
everything in place.
With the windings completed, the
next step is to scrape off about 5mm
of enamel insulation from the ends of
all four coil connections. That done,
place the bobbin inside one half of the
ferrite pot core and fit the assembly to
the PCB as shown in Fig.9, with each
wire or loop connection fed into its
matching PCB hole.
The top half of the pot core is then
fitted in position and the entire coil
assembly secured to the PCB using
an M3 x 25mm Nylon machine screw,
two Nylon flat washers and an M3
Nylon nut. Note that the screw should
be passed up through the PCB from
underneath, as shown in Fig.9.
Finally, solder the various leads
siliconchip.com.au
running from L1 to the PCB pads on
both sides of the board.
Completing the PCB assembly
The PCB assembly can now be completed (apart from its central shield)
by fitting VR1 and LED1. Before fitting
VR1, cut its shaft to a length of about
9mm and remove any burrs. VR1 can
then be soldered into position, after
which a short length of tinned copper
wire is used to connect the pot’s metal
shield can to the earth copper of the
PCB, via earth terminal pin TPG1.
Note that you may have to scrape
away the passivation from a small area
of the pot’s metal shield and apply
some flux in order to achieve a good
solder joint. You will also need a really
hot soldering iron.
LED1 is mounted vertically with
20mm lead lengths (use a cardboard
spacer). Be sure to orientate it with its
anode lead (A) to the right. Once it’s
in place, bend its leads forward by 90°
about 8mm above the PCB so that it
will later protrude through its matching hole in the front panel.
The next step is to make the central
shield for the PCB plus top and bottom horizontal shields to ensure good
performance. We’ll detail these shields
and complete the construction in Pt.2
SC
next month.
Helping to put you in Control
LED Power Supply
40 W, IP67 power supply
with Australian standard
plug on 1.8 m lead. Designed to work as constant
voltage or constant current
for driving LEDs. Cooling by free air convection. 12 VDC output at up to 3.33 A. Other
models are also available.
SKU:PSL-0412 Price: $106.20+GST
Ultrasonic Range Finder
5 m range, narrow beamwidth, IP67 ultrasonic rangefinder with 1 mm resolution
and filtering tuned to detect
snow depth levels.
Analog voltage, pulse width
and TTL serial outputs. 2.7-5.5 VDC powered. Matches 3/4” PVC pipe fittings.
RoHS compliant.
SKU:MXS-114
Price:$159.95+GST
Mini PLC - Arduino Compatible
Fitted with Ethernet, USB &
RS-485 interfaces, our new
controller features; 8 relay
outputs, 4 opto-isolated
inputs and 3x 4-20 mA or
0-5 VDC analog inputs.
Windows, Mac OS X and Linux compatible.
Accepts XBee form factor expansion boards.
12/24 VDC powered. DIN rail mountable.
SKU:KTA-323
Price:$185.00+GST
Universal Double Level Terminal
SKJ universal DIN rail
double level Screw terminal offers a wire section of
4 mm2 with 4 side cable
entry. Rated to 1000 V <at>
41 A. Can be mounted on
standard hat type railyway
Other sizes are also available
SKU:TRM-011
Price:$1.69+GST
Ambient Light Sensor
4 to 20 mA loop powered
ambient light sensor. Screw
terminal connec-tions. Housed
in IP65 rated enclosure
SKU:KTA-274
Price:$99+GST
Bipolar Stepper Motor
4-wire NEMA34 industrial
grade stepper motor, ideal
for driving heavier loads.
Has a holding torque of
122 kg.cm (11.96 Nm or
1694 oz-in). Front and rear
shafts. Other bipolar stepper motors are also available.
SKU:MOT-135
Price: $179.00 + GST
AM882 Stepper Motor Drive
Fully digital microstepping
stepper motor driver with antiresonance tuning and sensorless stall detection. 20 to 80
VDC powered with current
output of 0.1 to 5.86 A RMS.
Automatic/PC tuning via free Pro-tuner
software. Over-voltage/current & phaseerror protections.
SKU:SMC-011
Price: $159.00 + GST
For OEM/Wholesale prices
Contact Ocean Controls
Ph: (03) 9782 5882
oceancontrols.com.au
October 2013 29
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