Microtelecom Perseus Software Defined Receiver
Reviewed by Steve Ford, WB8IMY
The Perseus SDR uses cutting edge receiver technology to offer excellent performance and a wide range of features. It covers 10 kHz to 30 MHz and can receive all popular analog and digital modes with appropriate software.
As depicted in ancient Greek dramas, Perseus was a hero who used a clever ruse to slay the hideous Medusa (she of the reptilian coiffure and statuesque stare) and went on to save his beloved Andromeda from a sea monster. The 21st century Italian-made Perseus is a receiver that is striving to create its own legend by taking an innovative approach to software defined radio (SDR). Whether or not the gods smile on this Perseus — only time will tell.
To set the stage for this "drama," some explanation is in order. Most amateurs think of a software defined receiver as a device that starts with conventional front-end hardware — a filter and/or preselector, followed by an RF preamplifier and finally a stage that converts the RF signal to in-phase (I) and quadrature (Q) signals at audio frequencies. These baseband signals are subsequently fed to a computer sound card that samples and digitizes them, making the resulting data available for sophisticated massaging by software. As Gerald Youngblood, K5SDR, stated in his 2002 QEX article, "Give me I and Q and I can demodulate anything."
The Perseus receiver uses a somewhat different method. It digitizes the RF the moment it exits the front end filters and preamplifier. A high-speed analog-to-digital converter (ADC) converts the RF to data
by taking 80 million samples of the signal each second. Next, the Perseus uses a field programmable gate array (FPGA) to create I and Q information that is streamed to the PC via a USB cable for processing. In other words, the signal becomes data before it even reaches the computer.
This approach to SDR has several benefits that are apparent right away...
■ Fewer parts housed in a compact enclosure. The Perseus hardware enclosure only measures 4.3 x 1.4 x 7.3 inches. Figure 1 is a look inside the box.
■ Fewer cables. No sound card audio cables required —just a single USB cable to your computer.
■ And saving one of the best benefits for last, the performance of the Perseus does not depend on the quality of your computer sound card. With a conventional SDR your sound card acts as the analog-to-digital converter, so a mediocre sound card will give a mediocre result. With the Perseus, the analog-to-digital conversion is handled by high-performance hardware within the radio itself. The sound card in your computer is only there to drive your speakers, so any sound card will do.
Setting Up the Perseus
The Perseus arrives in a small, unpretentious package with very little inside. There is the radio itself, a 5 V wall-wart power supply with interchangeable US or European plugs, a USB cable and a CD-ROM with the Perseus software, USB drivers and instruction manual.
Microtelecom recommends a minimum 2 GHz PC running Windows XP or Vista. If you want to push the Perseus to its performance limit, they recommend a 2.5 GHz dual-core system. (Our ARRL Lab tests shown in Table 1 were performed using a 1.86 GHz dual-core PC.) The minimum requirements shown in Table 2 are easily met with any recent computer.
For my tests, I used a 2 GHz Toshiba Satellite laptop computer with 1 GB of memory and Windows Vista Home Basic. This is typical for what now passes as a "budget" consumer laptop.
It is worth noting that the Perseus is not confined to a Windows environment. Any SDR application can be used as long as it can "talk" to the Perseus hardware. If Linux is your pleasure, Microtelecom encourages you to try the popular Linrad application at www.sm5bsz.com/linuxdsp/linroot.htm.
Once you have the Perseus applications loaded to the computer, simply plug in the USB cable on the rear panel (Figure 2). With the Perseus hardware attached, fire up the application of your choice (the main Perseus software or the spectrum analyzer) and the radio comes to life.
At first I tried receiving with just a 30 foot wire plugged directly into the radio's BNC RF INPUT port. This didn't work well because the antenna was too close to my RF-noisy laptop, resulting in a continuous S7 level noise floor. I tried using a 15 foot USB extension cable to put some distance between the laptop and the antenna. This reduced the noise substantially. When I connected the Perseus to my outdoor inverted V antenna, the laptop interference was finally inaudible.
The World at Your Fingertips
Hams who've read my product reviews know that one of my favorite yardsticks is the no-manual test. Yes, we should all read the manuals before we apply power to any equipment. In theory, however, a well designed piece of hardware or software should be sufficiently user friendly that it works right out of the box with as little study as possible.
The Perseus software passed the no-manual test admirably. Once you figure out how to click your mouse on the arrow keys at the lower edges of the spectrum display, you're in business. There is a digital frequency readout as well. If you double-click within the readout window, a direct frequency entry keypad appears. Just enter your desired frequency in kilohertz and click OK or turn your mouse wheel. There are a total of 10 ways to tune the radio by clicking and dragging
various parts of the display. If you prefer a more tactile tuning experience, the Perseus will also work with the Griffin Technology PowerMate USB controller acting as a traditional knob ($45 at www.griffintechnology. com/products/powermate).
The Perseus software creates an attractive "virtual radio" on your computer screen, as you can see in the accompanying illustrations. All functions are clearly labeled and the operation of the software overall is very intuitive. During my first 30 minutes of ex-
ploration, I only had to resort to the manual when I wanted to learn the finer points of a particular function.
The Perseus has an effective receive range of 10 kHz to more than 30 MHz. Within the spectrum display window you can monitor up to 800 kHz at a time.2 For most of my applications, however, I reduced the display bandwidth considerably to make it easier to tune narrow signals such as CW or digital.
There are eight receive modes available at the click of a software button: CW, Upper Sideband, Lower Sideband, AM, Synchronous AM, RTTY, FM and DRM (more about DRM in a moment). The Perseus also provides a USER mode that makes the raw I and Q data available for user-designed applications.
The turbocharged performance of the Perseus became evident when I used it to dig weak CW signals out of the noise one evening on 40 meters. Some of the signals that I could hear clearly with the Perseus were mere whispers when I switched to my conventional transceiver using the same antenna. Best of all, I could create ultra-narrow filters by simply clicking my mouse cursor in the Perseus bandwidth window and dragging the right and left-hand bars that represent the filter skirts. It was fascinating to tune into a crowded band, then narrow the filters slowly, listening as the nearby signals vanished. You can also "drag" the filter through the bands, hearing signals pop in and out of the filter window.
If you've never listened to shortwave broadcasts using synchronous AM (SAM), you don't know what you've been missing. When you tune in an AM signal and toggle the SAM mode button, the Perseus creates a stable reference carrier to effectively replace the one sent by the transmitting station. This greatly reduces the effects of fading, making the signal a pleasure to hear. Even music, which often suffers worst of all, is enhanced with SAM.
I used the Perseus in the RTTY mode to receive digital signals, but the software does not have a built-in RTTY decoder. To use the Perseus with a digital decoding application such as DigiPan, you have to find a way to share the receiver's audio output signal. You can do this with a clever piece of Windows software known as Virtual Audio Cable (VAC). VAC is available at software.muzy-chenko.net/eng/vac.html for $30. There is a free trial version, but it injects a nagging voice into the audio stream saying "Trial!" every 10 seconds or so. With VAC running in the background, I was able to eavesdrop on PSK31 conversations using DigiPan.
With the Perseus you can get a taste of digital shortwave broadcasts that use the DRM (Digital Radio Mondiale) format.
You've probably heard the wide, buzzing DRM signals from time to time on the HF bands. These broadcasts offer FM quality audio, text streams and more, but the Perseus cannot decode DRM directly. You must download the general-purpose DRM decoder at www.winradio.com/home/download-drm.htm and purchase a license key for.........
FULL ARTICLE... Copyright © 2008 by the American Radio Relay League Inc.