44 September 2010

configuration. It also detects the desired

audio channel. The SDRMAX-II program is

the one you work with directly with through

its complex graphical interface. The two

programs talk to each other using TCP/IP

protocols. You normally run both of them in

the same PC, but you can place them in sepa-

rate computers on a LAN — and across the

Internet, if your connection is fast enough.

(I measured a typical data rate of 333 kbit/s

between the programs.)

While currently the Windows-only

SDRMAX-II is the recommended software,

you do have (free) alternatives. They include

a “cross-platform” SDRMAX-III that works

with Linux, MacOS X, or Windows, and in-

dependent software such as Winrad (www.

winrad.org) and WinradHD (www.hdsdr.

de). Naturally, each program has its strong

points. I am a Linux fan, and I appreciate that

I can run SDRMAX-III on my Ubuntu system,

even if I have to compile it from source. How-

ever, I found that SDRMAX-II for Windows

was more mature and easier to use. I think it

looks better too, but that’s a matter of taste.

A major update called SDRMAX-IV is in

development.

Because SDR is CPU intensive, I wanted

to explore how it worked on a small comput-

er. I was able to run SDRMAX-II on my Cel-

eron M (1.5 GHz) laptop, using 40 to 60% of

its CPU power. Operation was fairly smooth

even on this small machine, especially after

I reduced the spectrum update rate. SRL

specifies the minimum configuration as a

1.6 GHz Atom 330 CPU with 512 MB RAM

(2.5 GHz Dual Core recommended).

All the QS1R code from SRL is open

source, so if you have the desire and exper-

tise, you can make modifications or even roll

your own software. That’s important, even for

non-programmers, because developers are

likely to provide new capabilities over time.

Skimmer Server (see the sidebar) is an

elegant product developed on the QS1R

platform. It takes complete control of the

QS1R, bypassing the SRL software. Because

this program uses much more of the FPGA’s

capability, up to 7 receivers with 192 kHz

bandwidth running in parallel, it needs a

beefy power supply. Even if you aren’t going

to use Skimmer Server, I recommend using a

supply with at least 2 A capacity — it leaves

your options open for future applications.

Learner’s Permit

Any advanced radio takes some time to

learn, and the QS1R is no exception. The

hardware connections are simple, but the

SDRMAX-II software definitely has a learn-

ing curve to climb. The operating screen is

complex, and it is not immediately clear how

to do even the basic functions such as tuning.

There is no built-in help system, except that

tooltips are displayed if your cursor hovers

over a particular control. The support Web

site offers an online help manual that helps,

but it is incomplete. The site’s FAQ list fills

in some of the gaps, but you’re going to

face a certain amount of trial and error and

e-mail consultation! A training video would

go a long way toward getting new users up

to speed.

Joy of the Open Road

I enjoyed learning to drive this radio, but

the real fun begins when you take it out on

the highway. Hooked to my antenna farm

(dipoles for 80 and 40 meters plus a three

element SteppIR Yagi), its receive perfor-

mance on the amateur bands was comparable

to my Ten-Tec Orion, except for reduced

sensitivity on the higher bands. My home

location is relatively quiet — no high power

transmitters in the area — and the bands were

not crowded.

Figure 1 — The SDRMAX-II software with QS1RServer behind.

For me, the major plus of the SDR is

the spectrum display and the waterfall. You

can monitor a band segment, a whole band,

or even multiple bands (up to 20 MHz of

spectrum) to monitor propagation using HF

broadcast or amateur stations. The waterfall

shows a time history. You can find some

very interesting modulation modes, swept

frequency radios and ionosondes. You can

even do radioscience — watch interference

patterns (selective fading) drifting across

the sidebands of a distant HF broadcast

signal, telling you how ionospheric clouds

are moving!

There are many other ways you can use

the QS1R. You can find a signal with an

unknown frequency, such as parasitic os-

cillations, very quickly. You can diagnose

obscure interference issues. Many interfer-

ence sources have broad spectra that can be a

little hard to understand with a narrowband

receiver. I discovered that a problem I had

been seeing on 10 meters was actually spread

out over several MHz, putting me on the

track to find some arc-like source. The QS1R

would serve as a fine panadapter attached

to another receiver’s first IF, but it would

be overkill for this relatively narrowband

application.

You can connect the audio output to your

computer’s audio input jack and use any au-

dio analysis program you like. For example,

DRM or other digital voice decoders, PSK31,

RTTY and other digital data modes should

be simple to decode. With its synchronous

AM detection, the QS1R makes an excellent

AM broadcast receiver.

Conclusions

There are a few rough edges with this

product, which I’ve touched on above. The

documentation is incomplete, although

the e-mail and Web based help ecosystem

is very useful. The receiver sensitivity is

relatively low, limiting performance in the

higher bands, and the input low-pass filter is

not sufficient to prevent aliasing of signals

above 62.5 MHz. If all you want is a good

general-coverage receiver, there are less ex-

pensive products on the market with better

specifications.

The compelling features of the QS1R

SDR have to do with its ability to quickly

survey the entire spectrum from 10 kHz to

62 MHz and to provide a very flexible display

with point and click signal tuning and setting

of bandpass filters. As a panoramic display of

one or more entire amateur bands, it can add

a lot of capability to your station. It is also a

useful piece of test equipment for your bench.

On top of that, the QS1R has a lot of untapped

horsepower for special applications, as the

Skimmer Server product shows.

Manufacturer: Software Radio Laboratory,

8776 Shillington Dr, Powell, OH 43065-9001;

tel 614-339-4324; www.srl-llc.com.

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