SiliconChip: SiDRADIO an integrated SDR using a DVB-T dongle

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
[Picture of Internals]
siliconchip.com.au

SDR


STANDARD A-B
USB CABLE
(SHORT)

9.500400
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
from your PC via the USB cable.

IF 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 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 software designed 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

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 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 don

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

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. 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.

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.

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.

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

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 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 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.


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


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   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 @
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