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From July 2008 QST © ARRL
PRODUCT REVIEW
Mark J. Wilson, K1RO
Product Review Editor
k1ro@arrl.org
Bottom Line
Key Measurements
Summary
Reviewed by Rick Lindquist, WW3DE
NCJ Managing Editor
As we said in May 1998 QST when
reviewing the first commercially available
strictly computer controlled Amateur Radio
transceiver, the Kachina 505DSP: “The
relegation of functionality from hardware to
software and firmware opens broad vistas of
future capability.” Are we there yet? Or did
our flight to nirvana get canceled? A decade
down the road, Kachina is kaput in the ama-
teur market, and the newer software defined
radio (SDR) technology remains far from
ubiquitous in the modern ham shack. FlexRa-
dio Systems now represents the vanguard of
equipment manufacturers prodding the Ama-
teur Radio community into the SDR era.
Let’s face it: Most equipment in today’s
ham stations reflects only incremental im-
provements in well-established wireless tech-
nology, form factor and human user interface.
Additionally a “knob mentality” persists,
despite Kachina’s confidence, expressed 10
years ago, that owners of its milestone radio
would embrace mouse-and-keyboard operating
to the extent that knobs would become “super-
fluous.” In 2005 FlexRadio Systems nudged
things off the dime again with its SDR-1000.
The FLEX-5000A raises the software-
FlexRadio Systems
FLEX
-5000A
HF/50 MHz Transceiver
defined ham radio bar another notch.
Expanding Your Vocabulary
Just as hams once fretted about grid drive,
overmodulation and key clicks, the very na-
ture of SDRs has given rise to a new crop of
issues with names like “latency” and “sam-
pling rate.” This is serious technology, and
it’s not necessarily for the faint of heart.
In an SDR, analog RF signals are con-
verted to a digital bit stream, and everything
happens at that level using digital signal
processing (DSP) techniques before conver-
sion back to analog. As FlexRadio explains,
its SDR is “essentially a direct-conversion
receiver, but the mixing of the LO [local os-
cillator] to create a 9 kHz IF makes it appear
a lot like a dual-conversion receiver.” Some-
thing called a quadrature sampling detector
(QSD) — 0°, 90°, 180° and 270° — is at the
heart of all FLEX models. This generates the
“I” in-phase composite and “Q” quadrature
signals. Are your eyes glazing over yet?
FlexRadio points out that direct-
conversion receivers like the SDR-1000
and FLEX-5000A don’t require band-pass
or roofing filters. Because the QSD doesn’t
respond to signals below its passband but is
susceptible to odd harmonics above its LO
70
140
70
123
123
123
123
140
20 kHz Blocking Gain Compression (dB)
2 kHz Blocking Gain Compression (dB)
2
20
-40 +30
I
3
2
-40
+35
I
3
20
50
110
I
3
2
2 kHz 3rd-Order Dynamic Range (dB)
20 kHz 3rd-Order Intercept (dBm)
2 kHz 3rd-Order Intercept (dBm)
50
110
I
3
20
99
94
99
39
†
33
39
†
20 kHz 3rd-Order Dynamic Range (dB)
-20
-20
-70
I
9
TX
Transmit 9th-order IMD (dB)
-35
TX
I
3
Transmit 3rd-Order IMD (dB)
-34
-54
pr032
80 M
20 M
Dynamic range and intercept
values with preamp off.
Intercept values were determined
using -97 dBm reference
Key:
† Off Scale
The FLEX-5000A builds on the suc-
cess of the SDR-1000, retaining the
top-shelf radio performance and adding
features. The package is far less compli-
cated, shedding the many wires, cables,
boxes and connectors that characterized
the SDR-1000. Be prepared to experiment
with the software and settings to get the
most from this radio, however.