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

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  1. SiDRADIO: an integrated using a DVB-T dongle incorporating a tuned RF preselector, an up-converter &; coverage from DC to daylight
  2.  
  3. Pt.1: By JIM ROWE
  4. [Picture of Internals]
  5. siliconchip.com.au
  6.  
  7. SDR
  8.  
  9.  
  10. STANDARD A-B
  11. USB CABLE
  12. (SHORT)
  13.  
  14. 9.500400
  15. FRONT END
  16. UNIT (INCLUDES
  17. DVB-T DONGLE)
  18.  
  19. 11 – 35MHz
  20.  
  21. SILICON
  22. CHIP
  23.  
  24. SiDRADIO
  25.  
  26. 3.4 – 11MHz
  27. 1.0 – 3.4MHz
  28.  
  29. LAPTOP (OR DESKTOP) PC
  30. RUNNING SDR# OR
  31. SIMILAR SDR APPLICATION
  32.  
  33. 300 – 990kHz
  34. 100 – 320kHz
  35.  
  36. IN-BAND TUNING
  37.  
  38. BAND SELECT
  39.  
  40. RF GAIN
  41. from your PC via the USB cable.
  42.  
  43. 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
  44. 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
  45. 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
  46. great deal of reader interest. Inevitably though, readers are now hankering for extra features such as band-switching and tuning, gain on
  47.  
  48. L6 1mH
  49. +12.5V
  50.  
  51. L1: 48T 0.3mm ECW WOUND ON BOBBIN OF FERRITE POT CORE (LF-1060);
  52. TAPS AT 17T & 4T
  53. L2: 14T 0.3mm ECW WOUND ON AN 18mm OD x 6mm FERRITE TOROID (LO-1230);
  54. TAP AT 4T.
  55. L3: 6.5T 0.3mm ECW WOUND ON A 7mm LONG FERRITE BALUN CORE (LF-1222);
  56. TAP AT 1.5T
  57. L4: 15T 0.3mm ECW WOUND ON A MINI COIL FORMER WITH SLUG & SHIELD
  58. CAN (LF-1227); TAP AT 4T.
  59.  
  60. 22k
  61. 150k
  62.  
  63. 1 µF
  64.  
  65. 100nF
  66.  
  67. MMC
  68.  
  69. RF GAIN
  70.  
  71. VR1
  72. 50k
  73.  
  74. 10nF
  75.  
  76. L5: 26T 0.3mm ECW WOUND ON AN 18mm OD x 6mm FERRITE TOROID (LO-1230)
  77.  
  78. 12mH
  79.  
  80. 100nF
  81.  
  82. 1.3mH
  83.  
  84. 100k
  85.  
  86. 10nF
  87.  
  88. L1
  89.  
  90. 1.8k
  91.  
  92. 47k
  93. 100k
  94. 110 µH
  95.  
  96. L2
  97.  
  98. LF/MF/HF
  99. INPUT
  100.  
  101. CON3
  102.  
  103. 1
  104.  
  105. 1
  106.  
  107. S2a
  108.  
  109. T1
  110.  
  111. 2
  112.  
  113. 2
  114. 3
  115. 4
  116.  
  117. 10 µH
  118.  
  119. L3
  120.  
  121. S2b
  122.  
  123. 3
  124.  
  125. 100nF
  126.  
  127. 4
  128.  
  129. G2
  130.  
  131. 27T
  132.  
  133. 27T
  134.  
  135. D
  136.  
  137. 5
  138.  
  139. 5
  140.  
  141. G1
  142.  
  143. TUNING
  144.  
  145. VC1
  146. 10-210pF*
  147.  
  148. 1 µH
  149.  
  150. L4
  151.  
  152. VHF/UHF
  153. INPUT
  154.  
  155. Q1
  156. BF998
  157.  
  158. 10nF
  159.  
  160. S
  161.  
  162. 100nF
  163.  
  164. 360Ω
  165.  
  166. 100nF
  167.  
  168. BAND SELECT
  169.  
  170. CON4
  171.  
  172. * BOTH SECTIONS IN PARALLEL, TRIMMERS SET TO MINIMUM
  173.  
  174. SC
  175.  
  176. 2013
  177.  
  178. SiDRADIO
  179.  
  180. Fig.3: the circuit diagram of the SiDRADIO. The tuned RF front-end is based on coils L1-L4 & tuning capacitor VC1. Q1
  181. amplifies the tuned RF signal and feeds it via T1 to the up-converter which is based on an SA612AD/01 or SA602AD/01
  182. double-balanced mixer (IC1) and oscillator XO1. IC1 then feeds the antenna input of the DVB-T dongle via relay RLY1.
  183.  
  184. 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
  185. 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
  186. (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.
  187.  
  188. 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
  189.  
  190. L5 470 µH
  191.  
  192. D1 1N5819
  193. K
  194.  
  195. LF-HF POWER
  196.  
  197. 4.7Ω
  198.  
  199. A
  200.  
  201. CON1
  202.  
  203. +5V
  204.  
  205. USB
  206. TO PC
  207.  
  208. S1
  209. 47 µF
  210. TANT
  211.  
  212. 180Ω
  213.  
  214. 22k
  215.  
  216. 7
  217. 8
  218. 1
  219.  
  220. +1.25V
  221.  
  222. 5
  223.  
  224. 2.4k
  225.  
  226. DrC
  227. SwC
  228. Cin-
  229.  
  230. 6
  231.  
  232. Ips
  233.  
  234. 1 µF
  235.  
  236. Vcc
  237.  
  238. MMC
  239.  
  240. (TYPE B)
  241.  
  242. A
  243.  
  244. IC2
  245. MC34063
  246.  
  247. Ct
  248.  
  249. λ LED1
  250.  
  251. 3
  252.  
  253. K
  254.  
  255. 390pF
  256.  
  257. GND
  258. 4
  259.  
  260. SwE
  261. 2
  262.  
  263. 390Ω
  264.  
  265. CON2
  266. REG1 LP2950-3.3
  267.  
  268. +3.3V
  269.  
  270. OUT
  271.  
  272. 1 0 0nF
  273. 4
  274. Vdd
  275. 1
  276.  
  277. 10nF
  278.  
  279. XO1
  280.  
  281. EN FXO-HC536R OUT
  282. -125
  283.  
  284. L7
  285. 390nH
  286. 3
  287.  
  288. 3.3pF
  289.  
  290. GND
  291. 2
  292.  
  293. GND
  294.  
  295. 47 µF
  296.  
  297. 10k
  298.  
  299. 2
  300.  
  301. InA
  302.  
  303. 10nF
  304.  
  305. 6
  306. OscB
  307.  
  308. 8
  309. Vcc
  310. 4
  311. OutA
  312.  
  313. IC1
  314. SA612AD
  315. OR SA602AD
  316. InB
  317.  
  318.  
  319. RLY1
  320. (JRC-23F-05
  321. OR SIMILAR)
  322.  
  323. K
  324.  
  325. 470pF
  326.  
  327. 1
  328.  
  329. (TYPE A)
  330.  
  331. 10 µF
  332.  
  333. 220nF
  334.  
  335. 125MHz
  336.  
  337. 10k
  338.  
  339. USB TO
  340. DVB-T
  341. DONGLE
  342.  
  343. +5V
  344.  
  345. IN
  346.  
  347. A
  348.  
  349. VHF/UHF
  350. OUTPUT
  351. TO DONGLE
  352.  
  353. T2
  354.  
  355. 11T
  356.  
  357. OutB
  358.  
  359. Gnd
  360. 3
  361.  
  362. D2
  363. 1N4004
  364.  
  365. 2T
  366.  
  367. 5
  368.  
  369. 7
  370. BAND
  371. BAND
  372. BAND
  373. BAND
  374. BAND
  375.  
  376. T1: WOUND ON AN 18mm OD x 6mm FERRITE TOROID T2: WOUND ON A 14mm LONG FERRITE BALUN CORE
  377. (LF-1220); PRIMARY 11T OF 0.3mm ECW,
  378. (LO-1230); PRIMARY & SECONDARY BOTH 27T OF
  379. SECONDARY 2T OF 0.8mm ECW
  380. 0.3mm ECW
  381.  
  382. BF998
  383.  
  384. LED
  385.  
  386. D1, D2
  387. A
  388.  
  389. K
  390.  
  391. 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.
  392.  
  393. Circuit details
  394. The full circuit diagram of our SiDRADIO is shown in Fig.3 and if
  395.  
  396. G2(3)
  397.  
  398. K
  399. A
  400.  
  401. G1(4)
  402.  
  403. GND
  404.  
  405. D(2)
  406. S(1)
  407.  
  408. IN
  409.  
  410. 8
  411.  
  412. 100kHz – 320kHz
  413. 300kHz – 1.0MHz
  414. 1.0MHz – 3.4MHz
  415. 3.4MHz – 11MHz
  416. 11MHz – 35MHz
  417.  
  418. XO1
  419.  
  420. SA612AD,
  421. SA602AD
  422.  
  423. LP2950
  424.  
  425. 1:
  426. 2:
  427. 3:
  428. 4:
  429. 5:
  430.  
  431. 4
  432.  
  433. 3
  434.  
  435. 4
  436. 1
  437.  
  438. 1
  439.  
  440. OUT
  441.  
  442. (TP)
  443.  
  444. 2
  445.  
  446. Table 1: Common DVB-T Dongle Tuner Chips & Their Frequency Ranges
  447. Tuner Chip
  448. Elonics E4000
  449.  
  450. Frequency Range
  451.  
  452. DVB-T dongle model in which chip is found
  453.  
  454. 52 – 2200MHz* EzCAP EzTV668 DVB-T/FM/DAB, many current 'no name' devices
  455.  
  456. Rafael Micro R820T
  457.  
  458. 24 – 1766MHz
  459.  
  460. ? (not known – but may be in many future dongles)
  461.  
  462. Fitipower FC0013
  463.  
  464. 22 – 1100MHz
  465.  
  466. EzCAP EzTV645 DVB-T/FM/DAB, Kaiser Baas KBA010008 TV Stick
  467.  
  468. Fitipower FC0012
  469.  
  470. 22 – 948MHz
  471.  
  472. Many of the earlier DVB-T dongles
  473.  
  474. * With a gap from 1100MHz to 1250MHz (approx)
  475.  
  476. 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.
  477.  
  478. Up-converter operation
  479. 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.
  480. 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.
  481.  
  482. 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.
  483.  
  484. 3
  485. 2
  486. 1
  487.  
  488. A
  489.  
  490. LED1
  491.  
  492. K
  493.  
  494. D1
  495.  
  496. L5
  497.  
  498. 5819
  499.  
  500. 26T
  501.  
  502. TPG1
  503.  
  504. 10nF
  505.  
  506. 47k
  507. TPG4
  508.  
  509. 1 µF
  510.  
  511. TUNING
  512.  
  513. 100nF
  514.  
  515. Q1
  516. BF998
  517. S
  518. G1
  519.  
  520. D
  521.  
  522. 100nF
  523.  
  524. VC1
  525.  
  526. 100nF
  527.  
  528. 100nF
  529.  
  530. G2
  531.  
  532. 100nF
  533.  
  534. 27T
  535.  
  536. T1
  537.  
  538. IC1
  539. SA612A
  540.  
  541. 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.
  542.  
  543. 1
  544. 2
  545. 3
  546. 4
  547. 5
  548.  
  549. TPG2
  550.  
  551. S2
  552.  
  553. 8
  554.  
  555.  
  556. ROTOR
  557. B
  558.  
  559. 7
  560.  
  561. All the parts except for bandswitch S2 and the VHF-UHF input connector (CON4) are mounted on a large PCB
  562.  
  563. 4T TAP
  564.  
  565. GND
  566.  
  567. Construction
  568.  
  569. BAND SELECT
  570.  
  571. ROTOR
  572. A
  573. 11
  574. 10
  575. 9
  576.  
  577. GND
  578.  
  579. 4T TAP
  580.  
  581. L4 1.0 µH
  582.  
  583. 1.5T TAP
  584. 15T
  585.  
  586. L3
  587. 14T
  588.  
  589. 6.5T
  590.  
  591. GND
  592.  
  593. GND
  594.  
  595. L1
  596.  
  597. L2
  598.  
  599. 4T TAP
  600.  
  601. 48T
  602.  
  603. 17T TAP
  604.  
  605. 10nF
  606.  
  607. 10nF
  608.  
  609. TPG3
  610.  
  611. 1
  612.  
  613. 27T
  614.  
  615. 11T
  616. (SA602A) 1
  617.  
  618. 10k
  619. 470pF
  620. 125MHz
  621.  
  622. 3
  623.  
  624. XO1
  625.  
  626. 3.3pF
  627.  
  628. 4
  629.  
  630. 2
  631.  
  632. 100k
  633.  
  634. 390nH
  635.  
  636. select switch, with the dongle receiving LF-HF signals when S1 is in the on position and VHF/UHF signals when it is off.
  637.  
  638. VR1 50k LIN
  639. LF-HF GAIN
  640.  
  641. TANT
  642.  
  643. 47 µF
  644.  
  645. +
  646.  
  647. L6
  648.  
  649. T2
  650.  
  651. TP 12V
  652.  
  653. VERTICAL
  654. SHIELD
  655. PLATE
  656.  
  657. 1mH
  658.  
  659. GND
  660.  
  661. 2T
  662.  
  663. 10 µF
  664. +
  665. LP2950
  666. -3.3
  667.  
  668. 220nF
  669. REG1
  670.  
  671. +
  672.  
  673. 150k
  674. 10nF
  675. 1.8k
  676.  
  677. 47 µF
  678.  
  679. SHORT LENGTH
  680. OF 75 Ω COAXIAL
  681. CABLE (RG6)
  682.  
  683. RLY1
  684.  
  685. COMMON
  686.  
  687. COIL
  688.  
  689. VHF/UHF
  690. OUTPUT
  691.  
  692. (TO DONGLE)
  693.  
  694. D2
  695.  
  696. 10k
  697.  
  698. 1 0 0nF
  699.  
  700. 390pF
  701.  
  702. 1 µF
  703.  
  704. 2
  705. 1
  706.  
  707. 2.4k
  708. 4.7Ω
  709.  
  710. 3
  711. 4
  712.  
  713. JRC-23F-05
  714.  
  715. RO
  716. F DN
  717. E T N ORF F H
  718. HF FRONT
  719. END
  720. FOR
  721. DESA B EBASED
  722. L G N OD T- BVD
  723. DVB-T DONGLE
  724. OIDAR DE
  725. NIFED ERRADIO
  726. AWTF OS
  727. SOFTWARE
  728. DEFINED
  729.  
  730. 100k
  731. 360Ω
  732. 10nF
  733.  
  734. CON1
  735.  
  736. 4004
  737.  
  738. 1
  739. 3190160
  740. 06109131
  741. 3
  742. 10
  743. 2 C
  744. C
  745. 2013
  746.  
  747. 22k
  748. 180Ω
  749.  
  750. CON3
  751. LF-HF INPUT
  752.  
  753. IC2
  754.  
  755. CON4
  756. VHF-UHF INPUT
  757.  
  758. MC34063
  759.  
  760. NC
  761.  
  762. 22k
  763.  
  764. USB IN
  765.  
  766. 390Ω
  767. NO
  768.  
  769. Fig.6: the parts layout & wiring diagram. Start with the SMD parts and make sure all polarised parts are correctly orientated.
  770.  
  771. LF/HF POWER
  772.  
  773. 4
  774.  
  775. S1
  776.  
  777. 1
  778.  
  779. DVB-T
  780. DONGLE
  781.  
  782. 3
  783. 2
  784.  
  785. USB OUT
  786.  
  787. CON2
  788.  
  789. 4
  790.  
  791. 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
  792.  
  793. 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
  794.  
  795. (VIEW FROM FRONT)
  796.  
  797. Fig.7: this diagram shows the mounting
  798. details for tuning capacitor VC1. It must be
  799. stood off the PCB by 3.5mm using M3 nuts
  800. and flat washers as spacers, so that its tuning
  801. wheel clears the bottom the case.
  802.  
  803.  
  804. 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
  805.  
  806. 1
  807.  
  808. 2
  809.  
  810. 1
  811.  
  812. 2
  813.  
  814. A
  815.  
  816. 2
  817.  
  818. 2
  819.  
  820. 1
  821.  
  822. 2
  823. 15T
  824. (FINISH)
  825.  
  826. 4T
  827. TAP
  828.  
  829. 2
  830.  
  831. TOP
  832. VIEW
  833. 1
  834.  
  835.  
  836. 1
  837.  
  838. 1
  839.  
  840. GND
  841.  
  842. GND
  843.  
  844. 1
  845.  
  846. 2
  847.  
  848. 3
  849.  
  850. SOLDER WIRE
  851. END TO PIN 1,
  852. WIND 4 TURNS
  853. AT BOTTOM
  854. OF FORMER
  855.  
  856. MAKE LOOP IN WIRE,
  857. BEND DOWN THROUGH
  858. SLOT 'A' THEN WIND
  859. ON 11 MORE TURNS
  860. (IN SAME DIRECTION)
  861.  
  862. AFTER WINDING ON 11
  863. MORE TURNS, SOLDER
  864. WIRE END TO PIN 2.
  865. ALSO SCREW SLUG
  866. INTO CORE.
  867.  
  868. WINDING DETAILS FOR COIL L4
  869.  
  870.  
  871. Software Is Crucial
  872. The software needed to configure
  873. a DVB-T dongle and PC combination as an SDR consists of two main
  874. components: (1) a driver which allows
  875. the PC to communicate via the USB
  876. port with the Realtek RTL2832U (or
  877. similar) demodulator chip inside the
  878. dongle; and (2) application software
  879. to allow the PC to perform all the
  880. functions of an SDR in company with
  881. the SiDRADIO and its DVB-T dongle.
  882. The driver must be installed first.
  883. The most popular driver for a DVB-T
  884. dongle with an RTL2832U demodulator chip (when used as an SDR)
  885. is the “RTLSDR” driver (nearly all
  886. dongles use the RTL2832U). The
  887. website at www.rtlsdr.org provides
  888. lots of information on this.
  889. Once the driver has been installed,
  890. the application software can be installed. The most popular application
  891. software is SDR#, available from
  892. www.SDRSharp.com
  893. The article on Software Defined
  894. Radio in the May 2013 issue of SILICON
  895. CHIP has all the details on installing
  896. the driver and application software.
  897.  
  898. That done, trim the start and finish
  899. ends to about 10mm and strip 6mm
  900. of enamel from each end and from the
  901. tap loop. The coil can then be fitted to
  902. the PCB, secured with Nylon cable ties
  903. and the leads soldered.
  904. •  Coil L5 can be tackled next. It simply consists of 26 turns of 0.3mm ECW,
  905. with no taps or other complications.
  906. As before, it’s secured to the top of the
  907. PCB using two small cable ties.
  908. •  RF output transformer T2 is wound
  909.  
  910. on a 14mm-long ferrite balun core
  911. (Jaycar LF-1220 or similar), with the
  912. winding wire passed up through one
  913. hole in the balun core and then back
  914. down through the other hole, and so on.
  915. The secondary consists of just two
  916. turns of 0.8mm ECW and should be
  917. wound first. Then you can wind the
  918. primary, which consists of 11 turns
  919. of 0.25mm ECW. Note that the leads
  920. of the two windings emerge from opposite ends of the balun.
  921. When you have finished both windings, trim the free wire ends to about
  922. 10mm and strip the enamel from each
  923. end. The completed balun can then be
  924. mounted on the PCB and its four wire
  925. leads soldered to their respective pads.
  926. Make sure that the balun is orientated
  927. with its 11-turn primary winding to
  928. the left and solder these wires on both
  929. sides of the PCB.
  930. •  Coil L3 is wound on one of the
  931. smaller 6mm-long ferrite balun cores
  932. (Jaycar LF-1222 or similar). In this
  933. case, you need to wind on 6.5 turns
  934. of 0.3mm ECW with a ‘loop tap’ made
  935. after 1.5 turns from the start (ie, from
  936. the GND connection).
  937. It’s just a matter of winding on the
  938. first 1.5 turns, then bringing the wire
  939. out and doubling it back after about
  940. 12mm to form the tap, then winding
  941. on the remaining five turns – see Fig.6.
  942. •  Coil L4 (band 5) is close-wound on
  943. a small RF coil former that’s fitted with
  944. a ferrite tuning slug and housed in a
  945. shield can (Jaycar LF-1227 or similar).
  946. Although this coil only has 15 turns of
  947. 0.3mm ECW with a loop tap, it’s a bit
  948. fiddly to wind because of the former’s
  949. small size and because the former has
  950. only two termination pins.
  951. Fig.8 shows the winding details for
  952. L4. The ‘loop tap’ is formed just after
  953.  
  954. Table 1: Resistor Colour Codes
  955.  
  956. o
  957. o
  958. o
  959. o
  960. o
  961. o
  962. o
  963. o
  964. o
  965. o
  966. o
  967. o
  968. siliconchip.com.au
  969.  
  970. No.
  971.   1
  972.   2
  973.   1
  974.   2
  975.   2
  976.   1
  977.   1
  978.   1
  979.   1
  980.   1
  981.   1
  982.  
  983. Value
  984. 150kΩ
  985. 100kΩ
  986. 47kΩ
  987. 22kΩ
  988. 10kΩ
  989. 2.4kΩ
  990. 1.8kΩ
  991. 390Ω
  992. 360Ω
  993. 180Ω
  994. 4.7Ω
  995.  
  996. 4-Band Code (1%)
  997. brown green yellow brown
  998. brown black yellow brown
  999. yellow violet orange brown
  1000. red red orange brown
  1001. brown black orange brown
  1002. red yellow red brown
  1003. brown grey red brown
  1004. orange white brown brown
  1005. orange blue brown brown
  1006. brown grey brown brown
  1007. yellow violet gold brown
  1008.  
  1009. four turns from the start/GND end (pin
  1010. 1) and is fed down through one of the
  1011. small slots (A) in the former’s base, so
  1012. that it can subsequently be fed through
  1013. its matching hole in the PCB. Again,
  1014. make this ‘loop tap’ about 12mm long,
  1015. then wind on the remaining 11 turns
  1016. and terminate the wire on pin 2.
  1017. That done, screw the supplied ferrite slug into the former, along with the
  1018. small piece of rubber thread supplied
  1019. to act as a ‘hold tight’. You should
  1020. then scrape the insulating enamel
  1021. from the ‘tap loop’ so that it’s ready
  1022. for soldering.
  1023. The completed coil assembly can
  1024. now be mounted on the PCB (just
  1025. below coil L3). Orientate it as shown
  1026. on Fig.6, so that the two pins and
  1027. the ‘tap loop’ each go through their
  1028. matching PCB holes (ie, pin 1 GND at
  1029. bottom right, 4T tap at top). Once it’s
  1030. in place, solder the three connections
  1031. underneath the PCB, making sure that
  1032. you get a good solder joint to both of
  1033. the tap loop wires.
  1034. The next step is to gently screw
  1035. down the ferrite slug inside L4 using
  1036. a Nylon alignment tool until it just
  1037. touches the surface of the PCB. That
  1038. done, slip the metal shield can over
  1039. the completed coil former, until its two
  1040. attachment lugs pass down through
  1041. the holes provided on each side. These
  1042.  
  1043.  
  1044. Capacitor Codes
  1045.  
  1046. Value
  1047. 1µF
  1048. 220nF
  1049. 100nF
  1050. 10nF
  1051. 470pF
  1052. 390pF
  1053. 3.3pF
  1054.  
  1055. µF Value
  1056.   1µF
  1057.   0.22µF
  1058.   0.1µF
  1059.   0.01µF
  1060.   NA
  1061.   NA
  1062.   NA
  1063.  
  1064. IEC Code EIA Code
  1065.   1u0
  1066.  105
  1067.   220n
  1068.   224
  1069.   100n
  1070.   104
  1071.   10n
  1072.  103
  1073.  470p
  1074.  471
  1075.  390p
  1076.  391
  1077.   3p3
  1078.  3.3
  1079.  
  1080. 5-Band Code (1%)
  1081. brown green black orange brown
  1082. brown black black orange brown
  1083. yellow violet black red brown
  1084. red red black red brown
  1085. brown black black red brown
  1086. red yellow black brown brown
  1087. brown grey black brown brown
  1088. orange white black black brown
  1089. orange blue black black brown
  1090. brown grey black black brown
  1091. yellow violet black silver brown
  1092. October 2013  27
  1093.  
  1094. Parts List For SiDRADIO
  1095. 1 low profile ABS instrument case,
  1096. 225 x 165 x 40mm (Jaycar HB5972 or similar)
  1097. 1 double-sided PCB, code
  1098. 06109131, 197 x 156mm
  1099. 1 set of front & rear PCB panels,
  1100. code 06109132 & 06109133
  1101. (200 x 30mm)
  1102. 1 DVB-T dongle (using an RTL2832U decoder chip and either
  1103. the R820T, E4000 or FC0013
  1104. tuner chips)
  1105. 1 short length of 75Ω coaxial
  1106. cable, with plug to suit RF input
  1107. of dongle
  1108. 1 HCMOS 3.3V crystal oscillator
  1109. module, 125MHz (Fox Electron­
  1110. ics FXO-HC536-125 or similar,
  1111. element14 2058072) (XO1)
  1112. 1 SPDT 5V mini DIP relay, JRC23F-05 or similar (Futurlec)
  1113. (RLY1)
  1114. 1 SPDT PCB-mount vertical acting
  1115. toggle switch (S1) (Altronics
  1116. S1320)
  1117. 1 2-pole 5/6-position rotary switch
  1118. (S2)
  1119. 1 USB type B socket, horizontal
  1120. PCB-mount (CON1)
  1121. 1 USB type A socket, horizontal
  1122. PCB-mount (CON2)
  1123. 1 BNC socket, PCB mount (CON3)
  1124. 1 PAL (Belling-Lee) socket, panelmount (CON4)
  1125. 2 instrument knobs, 20mm diameter x 18mm deep (Jaycar HK7786 or similar)
  1126. 3 toroidal ferrite cores, 18mm
  1127. diameter x 6mm deep (Jaycar
  1128. LO-1230 or similar)
  1129. 1 6mm-long ferrite balun core (Jaycar LF-1222 or similar)
  1130. 1 14mm-long ferrite balun core
  1131. (Jaycar LF-1220 or similar)
  1132. 8 small Nylon cable ties
  1133. 1 mini RF coil former with slug and
  1134. shield can (Jaycar LF-1227 or
  1135. similar)
  1136. 1 pair of ferrite pot core halves
  1137. with bobbin (Jaycar LF-1060 +
  1138. LF1062)
  1139. 1 50kΩ linear pot, 16mm (VR1)
  1140. 1 miniature PCB-mount tuning
  1141. capacitor with knob & mounting
  1142. screws (VC1) (Jaycar RV-5728
  1143. or similar)
  1144. 1 M3 x 25mm Nylon machine screw
  1145. 1 M3 Nylon nut
  1146. 2 M3 flat Nylon washers
  1147. 28  Silicon Chip
  1148.  
  1149. M3 NYLON
  1150. NUT
  1151.  
  1152. 19 PCB pins, 1mm diameter
  1153. 1 1mH axial RF choke/inductor (L6)
  1154. 1 390nH SMD inductor, 0805 (L7)
  1155. 2 M2.5 x 6mm machine screws
  1156. 10 6mm-long No.4 self-tapping
  1157. screws
  1158. 1 M3 x 6mm machine screw
  1159. 1 M3 spring lockwasher
  1160. 3 M3 nuts
  1161. 2 M3 flat washers
  1162. 1 90 x 36 x 0.8mm aluminium sheet
  1163. or tinplate (to make vertical
  1164. shield)
  1165. 1 rectangular piece of blank PCB,
  1166. 195 x 150mm (for top horizontal
  1167. shield)
  1168. 1 196 x 134 x 0.25mm copper foil
  1169. or tinplate (for bottom horizontal
  1170. shield)
  1171. 1 200mm-length 0.25mm-dia, ECW
  1172. 1 1m-length 0.3mm-dia. ECW
  1173. 1 100mm-length 0.8mm-dia. ECW
  1174. Tinned copper wire, hook-up wire,
  1175. etc
  1176. Semiconductors
  1177. 1 SA612AD/01 or SA602AD/01
  1178. double balanced mixer (IC1) (element14 2212081 or 2212077)
  1179. 1 MC34063 DC-DC converter (IC2)
  1180. 1 BF998 dual-gate VHF MOSFET
  1181. (Q1) (element14 1081286)
  1182. 1 LP2950-3.3 or LM2936-3.3 LDO
  1183. regulator (REG1)
  1184. 1 5mm green LED (LED1)
  1185. 1 1N5819 Schottky diode (D1)
  1186. 1 1N4004 silicon diode (D2)
  1187. Capacitors
  1188. 1 47µF 10V RB electrolytic
  1189. 1 47µF 16V tantalum
  1190. 1 10µF 16V RB electrolytic
  1191. 2 1µF MMC
  1192. 1 220nF MMC
  1193. 5 100nF MMC
  1194. 5 10nF MMC
  1195. 1 10nF SMD ceramic (1206)
  1196. 1 470pF disc ceramic
  1197. 1 390pF disc ceramic
  1198. 1 3.3pF C0G/NP0 SMD ceramic
  1199. (1206)
  1200. Resistors (0.25W, 1%)
  1201. 1 150kΩ
  1202.  
  1203. 2 100kΩ
  1204.  
  1205. 1 47kΩ
  1206.  
  1207. 2 22kΩ
  1208.  
  1209. 2 10kΩ SMD (0805)
  1210. 1 2.4kΩ
  1211.  
  1212. 1 1.8kΩ
  1213. 1 390Ω
  1214. 1 360Ω
  1215. 1 180Ω
  1216. 1 4.7Ω 0.5W
  1217.  
  1218. FERRITE
  1219. POT CORE
  1220. HALVES
  1221.  
  1222. NYLON
  1223. FLAT
  1224. WASHER
  1225.  
  1226. PCB
  1227.  
  1228. M3 x 25mm
  1229. NYLON SCREW
  1230.  
  1231. NYLON FLAT
  1232. WASHER
  1233.  
  1234. (TOP VIEW)
  1235.  
  1236. (START)
  1237. GND
  1238.  
  1239. 17.5T
  1240. TAP
  1241.  
  1242. 4T
  1243. TAP
  1244.  
  1245. 48T
  1246. (FINISH)
  1247.  
  1248. Fig.9: coil L1 is wound on the
  1249. bobbin of a 2-part ferrite pot core
  1250. (see text) and secured to the PCB
  1251. using an M3 x 25mm Nylon screw,
  1252. washers and nut.
  1253.  
  1254. are then soldered to their pads on the
  1255. underside of the PCB to secure the
  1256. can in place.
  1257.  
  1258. Winding coil L1
  1259. The remaining coil to be wound is
  1260. L1 – see Fig.9. It’s wound on the bobbin of a 2-section ferrite pot core assembly measuring 25mm in diameter
  1261. and 16.5mm high (Jaycar LF-1060 +
  1262. LF1062).
  1263. This coil is wound in a conventional
  1264. fashion directly on the bobbin and
  1265. consists of 48 turns of 0.3mm ECW
  1266. with two tapping loops. The winding
  1267. procedure is as follows.
  1268. First, anchor the ‘start’ end of the
  1269. wire to one side of the bobbin using
  1270. cellulose tape. That done, close-wind
  1271. four turns onto the bobbin, then bring
  1272. out a loop of wire to form the antenna
  1273. ‘tap’ via the same slot in the bobbin’s
  1274. side that was used for the ‘start’ lead.
  1275. Anchor this loop tap to the side of
  1276. the bobbin with another small piece
  1277. of cellulose tape, then close-wind on
  1278. 13.5 more turns in the same direction
  1279. as the first four turns.
  1280. After winding on these extra turns,
  1281. bring out another tap loop through the
  1282. slot in the opposite side of the bobbin
  1283. (ie, opposite the ‘start’ and ‘4T tap’
  1284. wires). Anchor this loop to the outside
  1285. of the bobbin using cellulose tape, then
  1286. siliconchip.com.au
  1287.  
  1288. 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.
  1289.  
  1290. Completing the PCB assembly
  1291. 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.
  1292.  
  1293. Helping to put you in Control
  1294. LED Power Supply
  1295.  
  1296. 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.
  1297. SKU:PSL-0412 Price: $106.20+GST
  1298.  
  1299. Ultrasonic Range Finder
  1300.  
  1301. 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.
  1302. SKU:MXS-114
  1303. Price:$159.95+GST
  1304.  
  1305. Mini PLC - Arduino Compatible
  1306.  
  1307. Fitted with Ethernet, USB &
  1308. RS-485 interfaces, our new
  1309. controller features; 8 relay
  1310. outputs, 4 opto-isolated
  1311. inputs and 3x 4-20 mA or
  1312. 0-5 VDC analog inputs.
  1313. Windows, Mac OS X and Linux compatible.
  1314. Accepts XBee form factor expansion boards.
  1315. 12/24 VDC powered. DIN rail mountable.
  1316. SKU:KTA-323
  1317. Price:$185.00+GST
  1318.  
  1319. Universal Double Level Terminal
  1320.  
  1321. SKJ universal DIN rail
  1322. double level Screw terminal offers a wire section of
  1323. 4 mm2 with 4 side cable
  1324. entry. Rated to 1000 V @
  1325. 41 A. Can be mounted on
  1326. standard hat type railyway
  1327. Other sizes are also available
  1328. SKU:TRM-011
  1329. Price:$1.69+GST
  1330.  
  1331. Ambient Light Sensor
  1332.  
  1333. 4 to 20 mA loop powered
  1334. ambient light sensor. Screw
  1335. terminal connec-tions. Housed
  1336. in IP65 rated enclosure
  1337. SKU:KTA-274
  1338. Price:$99+GST
  1339.  
  1340. Bipolar Stepper Motor
  1341.  
  1342. 4-wire NEMA34 industrial
  1343. grade stepper motor, ideal
  1344. for driving heavier loads.
  1345. Has a holding torque of
  1346. 122 kg.cm (11.96 Nm or
  1347. 1694 oz-in). Front and rear
  1348. shafts. Other bipolar stepper motors are also available.
  1349. SKU:MOT-135
  1350. Price: $179.00 + GST
  1351.  
  1352. AM882 Stepper Motor Drive
  1353.  
  1354. Fully digital microstepping
  1355. stepper motor driver with antiresonance tuning and sensorless stall detection. 20 to 80
  1356. VDC powered with current
  1357. output of 0.1 to 5.86 A RMS.
  1358. Automatic/PC tuning via free Pro-tuner
  1359. software. Over-voltage/current & phaseerror protections.
  1360. SKU:SMC-011
  1361. Price: $159.00 + GST
  1362.  
  1363. For OEM/Wholesale prices
  1364. Contact Ocean Controls
  1365. Ph: (03) 9782 5882
  1366. oceancontrols.com.au
  1367.  
  1368. October 2013  29
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