Fullscreen HTML5Med Res (??MB)HTML4

“ ” 90% of the performance . . . at 5% of the cost   RF Explorer: The spectrum analyser that fits in the palm of your hand H ow much would you expect to pay for a sophisticated blight Mike Jagger’s vocals, a wireless door-bell frustrate a portable, but PC linkable UHF spectrum analyser? security system, a theatre’s softly-spoken Lady Macbeth be cursed by a cell phone texting or a nearby radio amateur Thousands? torment a studio broadcast. UHF “frequency domain” (frequency versus signal However, for those of us not setting up Rolling Stone strength) test gear analysers can indeed be very costly and concerts or theatrical events, UHF spectrum analysis test sometimes bulky and difficult to master. Typical of budget spectrum analysers is the well thought gear can be dauntingly costly. Budget monitoring at sub-GHz frequencies can normally of TTi PSA2702, costing almost $2000. Advanced test gear is called for when sensing and dis- only be done with a UHF scanner and scanning (although playing weak, complex, interfering or transient signals over rapid) usually requires prior entry of channels. Although Uniden’s range offer “close call” features, weaker interferwide-band UHF (300MHz to 3GHz). For RF transmission, circuit and antenna testing, a spec- ence nearby may be missed. UHF scanners are also usually optimised for FM receptrum analyser is viewed as an essential tool, comparable to a multimeter for DC or oscilloscope for AC. When setting up tion and the increasing sub-1Ghz digital data transmissions professional cellular networks, TV, telemetry links or live may be ignored. This is of particular significance around 700MHz, as event broadcast and control systems it would be foolish to there’s a move to free up UHF analog TV spectrum for more even consider skin-flint approaches. Steep commercial RF test equipment prices may be tol- efficient digital TV and 4G cellular use. erable for professionals on reliability grounds – it’d be a RF Explorer concert nightmare if potential stage mic It’s therefore pleasing to see the cost-efinterference was missed by simpler gear. “Hands On” Review fective “RF Explorer”. At prices an order Unless checked and isolated, the likes by Stan Swan of magnitude cheaper than professional of CB chatter from a passing truckie could 82  Silicon Chip siliconchip.com.au analysers but with features approaching those of the big boys, the RF Explorer increasingly looks like a game changer! Background RF Explorers are the brainchild of Spanish engineer Ariel Rochell, who designed them to monitor the nearby RF spectrum while flying radio controlled models. In many parts of the world 433MHz and 868MHz bands are a “soup” of potentially interfering signals and such band monitoring can be extremely beneficial in preventing plane loss or accidents. Uptake of the RF Explorer has been rapid, not only by radio control modellers but also general UHF users. The device is now manufactured by Seeed Studio – a Chinese electronics supplier. Agents are also active in most countries, including Australia and New Zealand. The units come in several variants, with the top WSUB3G/3G covering from 15MHz to 2.7GHz and costing $US269 (on the manufacturer’s website with free shipping). The slightly more sensitive, much cheaper ($US129) WSUB1G model evaluated here covers from 240MHz to 960MHz and looks the most appealing and cost-effective version for many UHF users. An add-on 2.4GHz expansion module (and second antenna) is available if required. The Explorer uses a powerful Microchip PIC24FJ64GA004 16-bit microcontroller to control the SiLabs (Silicon Labs) Si4432 transceiver. Some model variants use this as an internal signal calibrator. SiLab’s thumbnail-sized Si4432 is a popular RF engine in many current UHF devices, with Chinese firm Dorji using them in their 433MHz data transceivers. (Dorji’s recent DRF4463D20 in fact uses a newer SiLab Si4463 RF IC, although the Si4432 has superior frequency coverage). The units are nicely assembled, with a very clear backlit mono LCD and outstanding battery life. Perhaps the only initial concerns relate to a very small on/off switch, buttons that tend to “click”, a bottom mini-USB socket and the lack of audio output. Features and specifications The RF Explorer makers claim “90% of what a high cost unit will do at 5% of the price”. Can they be any good at such user-friendly prices? A feature check of the budget WSUB1G model is reassuring:: • Pocket size and light weight (185g) – solid aluminum metal case (113 x 70 x 25mm). • Wide band coverage, from 240MHz to 960MHz - suiting all popular sub-1GHz ISM bands (315, 433, 868 and 915MHz), plus UHF TV, PRS, 70cm and 33cm ham radio, GSM etc. • Spectrum analyser mode with Peak, Max, Hold, Normal, Overwrite and Averaging modes. • User-friendly push-button controls. • High capacity lithium polymer battery, USB 2.0 rechargeable. • Open-source Windows (XP/Vista/Win7) and Mac client software. • Selectable frequency span: 112kHz - 100MHz • Mono (backlit) 128x64 pixel graphics LCD for good visibility outdoors. • Standard SMA 50Ω connector – wideband Nagoya NA-773 telescopic antenna included siliconchip.com.au It was originally developed to check the spectrum around 433MHz for radio-controlled aircraft operations. • • • • • • • • • Amplitude resolution: 0.5dBm. Dynamic range: -115dBm to 0dBm Absolute maximum input power: +5dBm. Average noise level (typical): -110dBm Frequency stability and accuracy (typical): ±10ppm Amplitude stability and accuracy (typical): ±3dBm Frequency resolution: 1kHz. Resolution bandwidth automatic 2.6kHz to 600khz Extendable via internal expansion modules for additional bands and functionality. • Lifetime free firmware upgrades available, open to community requested features. The online firmware upgrades are particularly appealing, and anticipated future extensions include: • Transmission test tones in OOK and FSK ( On-Off and Frequency Shift Keying) • Digital transmission decoding and packet sniffing for OOK and FSK, including Manchester code support • Logging features for multi-hour transmission monitoring • Frequency counter and automatic peak detection • Storage for up to five screenshots in internal memory or thousands of screenshots in expanded memory. • Expansion modules for additional ISM band support, ex- A close-up of the RF Explorer screen showing, in this case, a Wi-Fi signal on 2430.749MHz. This is made possible with an add-on module – the normal upper limit for the economy model RF Explorer reviewed here is 960MHz. May 2013  83 “Front panel key presses show on the LCD screen, and control configuration of frequency span and bandwidth,as well as selecting diverse signal display options. Here’s a narrow bandwidth GFSK (Gaussian Frequency Shift Keyed) data signal. Note how little spectrum space this superior filtered signal occupies. The narrower bandwidth makes for a more sensitive receiver as well. panded RF Generator and Tracking Generator for circuit analysis, etc. Hands on Seven front panel keys control operation, which is fairly intuitive. “Menu” initially selects operational mode (with only one being available on the budget model) and further clicks to comprehensive Frequency, Attenuator and Configuration menus. Up and down arrow keys allow option selections, “Enter” toggles through (and also freezes a display) while “Return” goes back. The left and right arrow keys control displayed frequency span and bandwidth (ranging from 600kHz down to 2kHz). The higher setting allows 100MHz wide band monitoring, while the narrower setting shows increasingly tighter spectrum slices that suit individual signal analysis. Displayed frequency was found pleasingly accurate, with resolution being best at the lowest 2kHz bandwidth. A handy way to confirm calibration is via a UHF CB PRS transceiver on low power. However this should NOT be too close to the RF Explorer as overload may occur. Perhaps even remove the SMA antenna entirely? A check with several 40-channel Uniden UH039P transceiver on channel 24 (nominally 477.000MHz) showed all uniformly transmitting on a close 477.005MHz . Many users will soon settle on a band of interest, and be content to use the unit as a portable monitor, perhaps when setting up 433MHz equipment. However connecting via USB cable both charges the inbuilt battery and allows comprehensive client (Windows/Mac) software to be run. (Above): a switch and USB connector are on the bottom of the case, necessitating it be raised above bench level. Fortunately, a low-cost “desk stand” is available to support the RF Explorer (see right). 84  Silicon Chip In contrast a similar FSK (Frequency Shift Keyed) data signal has`a much wider bandwidth, and may be wasteful of spectrum.” (Windows requires Microsoft’s .NET Framework version 4 (or higher) to be installed.) Client software is not just limited to the official version, as Stage Research’s “RF Scanner” allows for both continuous monitoring of the spectrum and valuable alerts when designated signals go beyond a programmable threshold. Applications The unit proved especially convenient for quick spectrum checks to see “just what’s going on” nearby. This relates not just to signal detection but thanks to the signal strength reading, detailed display of signal level. Changes to the latter may arise from alterations to transmitter power, antenna or feed lines but may also relate to propagation obstructions. Path obstructions become increasingly significant at high UHF, as even seasonal vegetation changes or weather may significantly attenuate signals. The rise of “all or nothing” digital TV at ~600MHz increasingly requires good signal levels and rooftop antenna sweet spots to be located; tasks readily performed with an RF Explorer. The Nagoya telescopic whip strictly covers 144- 430MHz but is usually satisfactory for quick spectrum checks at other frequencies. Naturally, specific band antennas should be used on higher frequencies. As these will be short (at 900MHz a quarter wavelength is just ~75mm long), simple resonant lengths can easily be made from scrap wire and connected via adaptors. Various SMA adapters are readily available, with Jaycar’s SMA socket to BNC socket (PA-0624) particularly suitable. A short extension lead could also be used to ease wear and (Above): a simple jumper lead is essential if you are continually swapping antennas. siliconchip.com.au tear on the unit’s SMA antenna socket, as this may eventually fail with continual antenna changes. Interference location All manner of signals abound on the licence-free 433MHz ISM band, and interference may blight activities. Hobbyists may also yearn for a simple “is my %$#<at>&! transmitter actually working?” A BNC to Banana socket adapter (Jaycar PA-3666) or BNC-Spring terminal (Jaycar PA-3715) readily accepts stiff wires at its double binding posts and with these each trimmed to ~160mm a simple half-wave dipole results. (The adapter’s internal wiring contributes some antenna length too of course). Rotation of this antenna to maximize displayed signal level, along with simple readings from several locations readily allows a fix on the nearby interference source. Naturally a more directive Yagi antenna could do this with some precision! Transmitter Placing the RF Explorer near a 433MHz transmitter will readily show the signal presence, nature, duration, frequency and relative strength. Improvements in signal strength may well relate to finding an unobstructed and elevated take off position for the likes of a backyard wireless weather station. For omni-directional work at 433MHz a simple quarterwave vertical whip is common, although some uncertainly often arises over the best length, especially in tight enclosures. Connecting a stiff piece of bell wire to a BNC-RCA adapter (Jaycar PA-3654) readily allowed it to be snipped progressively shorter while monitoring the received signal strength. Much as theory predicted, the best performance occurred at ~165mm. In a world filled with wireless radio signals, there is a real need to quickly search for clear bands, find interference and measure signals. Wireless microphones, video links, phone networks, Wi-Fi, ZigBee, Bluetooth, ISM bands, remote control hobbies and more all clutter the airwaves… Introducing The RF Explorer - RF Spectrum Analyser - Affordable - Handheld and portable - Capture and analyse data - Long-life rechargeable battery - Upgradeable and updateable - Free downloadable Mac and Windows software Available in various frequency versions, the RF Explorer is a useful addition to your toolbox. The various models and their frequency coverage: Conclusion At such a bargain price and considering the enhanced features, the RF Explorer looks like an indispensable portable test item for almost anyone working with higher frequency radio signals. The increased popularity of the 700-900MHz spectrum makes them especially prized, as off-the-shelf monitoring gear in this sub-GHz band can be elusive or costly. Antenna designers and installers alone may find them an answer to their prayers, as they quickly assess relative antenna and feed line performance, as well as locating UHF signal sweet spots that terrain may otherwise obscure. As a tribute to the RF Explorer’s niche popularity the NZ agent (Sound Techniques-Auckland) reports that interest arising just from passing inspection of my evaluation unit has already lead to several local sales. These little darlings sell themselves! Where can you get one? The choice is via local agents or online. The designer has just emailed me to say “We have an official distributor in Australia, www.soundlabsgroup.com.au”. However, SoundLabsGroup doesn’t have a dedicated page for RF Explorer yet but hope to have one up by the time this issue is released. Alternatively, in New Zealand Sound Techniques (www. soundtq.co.nz) will be able to help you out. SC siliconchip.com.au www.soundlabsgroup.com.au Sydney: (02) 4627-8766 Melbourne: (03) 9859-0388 May 2013  85