Flexradio Flex-3000 review

EQUIPMENT REVIEW PETER HART, G3SJX ♦ E-MAIL: [e-mail] AUGUST 2009 ♦ RADCOM

FlexRadio FLEX-3000 HF
and 50MHz SDR Transceiver

quadrature transmit signal from the PC via
the Firewire bus and on-board 24-bit D/A
converters to give the transmit signal source.
This is then amplified using power MOSFET
transistors and low-pass filtered to give the
required 100W output power. An auto ATU
is built in, using relay-switched inductors

and capacitors.

The radio is powered from an external

13.8V power supply, drawing up to 25A
on transmit. The circuitry is contained on
two printed circuit boards mounted on a
base plate and a thin heatsink is blown
by two fans which are quite noisy,
particularly on transmit. This assembly
fits into a wrap-around case measuring
311mm (w) x 44mm (h) x 311mm (d).

INTRODUCTION. FlexRadio Systems has

recently added another transceiver to their
range of innovative software defined radios.
The FLEX-3000 is a new model, smaller and
lower in cost compared to the FLEX-5000A
that was reviewed in the January 2008
and March 2009 issues of RadCom. The
FLEX-3000 received CE certification in May
and first deliveries to Europe started in June.
With a footprint and height similar to a laptop
PC, it uses the same architecture as the
FLEX-5000A and feature set provided by
the same PowerSDR software.

COMPARISON WITH FLEX-5000A. The

FLEX-5000A uses a modular construction
with plenty of space to add additional boards
such as anATU, second receiver andtransverter.
The FLEX-3000 uses two PCBs mounted on
a flat bottomplate with noprovisionfor
expansion. A single hardware receiver is
accommodated but the PowerSDR software
allows for two separate and isolated receive
channels within a 96kHz receive window. No
duplex, cross-band or cross-mode operation is
possible. The FLEX-3000 does, however,
include a built-in auto ATU that is only
selectable if the antenna match is poor. There
is a single antenna socket (BNC connector),
no provision for separate receiver antenna
and the audio line input/output and switching
interfaces are more limited for the FLEX-

3000. However,
the receiver frequency range and transmit
output power are the same. The panadaptor
spectrum display is limited to 96kHz and
the front-end filtering in the FLEX-3000 is
significantly reduced. The claimed dynamic
range figures are lower than for the FLEX­5000A, probably because a lower specified

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ADC is used, but the cost is considerably less.

SYSTEM HARDWARE. The FLEX-3000 is

used in conjunction with a PC and a Firewire
bus provides all control for the hardware
and the digitised transmit and receive IF
paths. A sound card is not required in the
PC. The receiver tunes from nominally
100kHz to 60MHz. Incoming signals are
down-converted to a low IF using a pair of
quadrature sampling detectors as an image
rejection mixer. The IF is set by default to
9kHz but can be set by the software to be in
the range 0Hz to 20kHz. Image rejection is
the principal weakness with this architecture
although software trimming reduces the
image to quite low levels. A spur reduction
mode is provided that allows the IF to vary
between about 9 and 16.6kHz, coarse
stepping the DDS in 7.6kHz steps and fine
tuning by the DSP at the IF. This moves the
image frequency and hopefully helps when
image or other spurs are a problem. The
resulting I and Q outputs from the mixers
are fed to 24-bit A/D converters and thence
to the PC for all signal processing. Local
oscillator drive in quadrature to the two
mixers is obtained directly from a high
frequency Direct Digital Synthesiser (DDS)
IC tuning in 1Hz steps. The receiver front-end
uses 5th order bandpass filters (7th order
on 160m) and a total of seven filters covers
the tuning range of the radio. In comparison,
the FLEX-5000 uses higher performance
11th order filters, one for each amateur
band. A nominal 26dB gain front-end
preamplifier can be selected on bands
above 160m, or a 20dB front-end attenuator
for very strong signals.

On transmit, a similar pair of quadrature

mixers and DDS is used to up-convert the

The only controls on the front panel are
the illuminated on/off switch, headphone
jack, RJ-45 microphone socket (Yaesu
compatible pinning) and CW key jack.
The rear panel contains a BNC antenna
socket, PTT input, TX grounded output,
audio line in (via FlexWire socket) and
audio line out. Computer style powered
speakers can be connected to the audio
line out socket. The 9-pin D connector
FlexWire interface provides control for a
future range of accessories using I
control. The Firewire computer interface
uses the IEEE1394a 400Mb/s standard
and not the higher speed 1394b standard.

SYSTEM SOFTWARE. Apart from the

hardware functions already described, the
remaining features and functions of the
radio are defined largely by the PowerSDR
software, which runs on the PC. This
software is common to the FLEX-5000
and hence both radios share the same
user interface and software-related feature
set. PowerSDR is constantly being developed
and improved as freely available GPL open
source code. Code updates are quite frequent
and are released via the FlexRadio website
at www.flex-radio.com. The feature set is
quite awesome, there are probably more
features and functions than any other top
end radio currently available. The core feature
set was described in the FLEX-5000A review
in the January 2008 RadCom and will not
be repeated here but a full description of all
the features is included in the FLEX-3000
user manual, which runs to nearly 200
pages. Paper manuals are not included with
the radio, except for a quick start guide. All
files and manuals are provided on CDROM

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C bus

EQUIPMENT REVIEWRADCOM ♦ AUGUST 2009

but the latest versions of all are readily
downloadable from the FlexRadio website.

The first step to getting the radio up and
running is to install the driver and system
firmware either from the supplied CDROM
or from the FlexRadio website. All software
is compatible with Windows Vista and XP
operating systems. The next step is to install
the PowerSDR software and then finally
a few configuration set-ups. The whole
process takes about 10 minutes. The radio
is supplied fully calibrated, including image
nulling, although this can be optimised with
some care.

FlexRadio have completed an adaptive
nulling routine termed ‘Wide Band Image
Rejection’ or WBIR and this was demonstrated
at Dayton this year. This will reduce images
down to the noise floor automatically as
the frequency is changed and will be issued
this summer.

A fast PC is a definite advantage as it
minimises time delays (latency) and enables
additional applications such as RTTY or PSK
to be used via the Virtual Audio Cable without
problems. A Firewire IEE1394 interface is
of course required and the radio is provided
with a 6 pin lead. A 6-pin to 4-pin adaptor
or separate lead will be needed with laptop
computers where this smaller socket is fitted.
I used my Dell laptop PC with a 1.3GHz
Celeron M processor, which is quite old now,
with generally satisfactory results, but a faster
PC would be better.

MEASUREMENTS. The measured

performance is shown in the table. The
preamplifier gain is some 10dB higher than
the FLEX-5000A and although the sensitivity
is similar with the preamplifier off, it is
significantly better than the FLEX-5000A
with the preamplifier on. The sensitivity

drops rapidly at
lower frequencies
below 500kHz
and is not really
usable at LF.
Additional front­end bandpass
filters are needed
for MF broadcast
reception to
suppress images
and harmonic
breakthrough. The
image rejection at
18kHz below the
receive frequency
varied across the
bands from 44dB
to 69dB with the
factory default
calibration, which
falls rather short of
the published
specification of

70dB. It is
possible, with some degree of effort, to null
out the image to over 70dB but the settings
do not hold over the band (but see comment
in the Conclusions). Switching-style mixers
respond to harmonic frequencies. Rejection of
2nd and 3rd harmonics was typically some
70 to 90dB (worst case 65dB). The higher
order filters used in the FLEX-5000
remove any harmonic response
entirely. A number of weak spurious
signals or birdies were audible on
most bands and visible on the
spectrum display but, to be fair,
these were largely below band noise
level except on the quieter higher
frequency bands.

The S-meter showed a very linear
indication with 50µV for S9 and 6dB
per S unit. The display indicates
signal input in dBm with an excellent
accuracy of about ±2dB. The AGC
attack characteristic interrupts the
signal for 5 to 10ms change to and
can impair readability of weak
signals under noisy conditions.
I have seen this effect on a number

FLEXRADIO SYSTEMS FLEX-3000 MEASURED
PERFORMANCE

RECEIVER MEASUREMENTS

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1.8MHz - 1.1µV (-106dBm)

3.5MHz 0.70µV (-110dBm) 1.1µV (-106dBm)
5MHz 0.28µV (-118dBm) 1.0µV (-107dBm)
7MHz 0.16µV (-123dBm) 1.0µV (-107dBm)
10MHz 0.16µV (-123dBm) 1.3µV (-105dBm)
14MHz 0.13µV (-125dBm) 1.0µV (-107dBm)
18MHz 0.13µV (-125dBm) 1.4µV (-104dBm)
21MHz 0.13µV (-125dBm) 1.3µV (-105dBm)
24MHz 0.11µV (-126dBm) 1.4µV (-104dBm)
28MHz 0.14µV (-124dBm) 2.2µV (-100dBm)
50MHz 0.13µV (-125dBm) 2.8µV (-98dBm)

AM sensitivity (28MHz): 0.7µV for 10dBs+n:n at 30% mod FM
sensitivity (28MHz): 0.16µV for 12dB SINAD 3kHz pk dev
Inband intermodulation products: <-50dB

TRANSMITTER MEASUREMENTS

of IF DSP radios. Channel selectivity
measurements were not made as
this is determined by the PowerSDR
software and will be the same as for
the FLEX-5000A.

Reciprocal mixing measurements
were independent of frequency
spacings from 1kHz out to beyond
300kHz. On 21MHz this yielded a
phase noise limited dynamic range of
87dB in 2.1kHz bandwidth (93dB in
500Hz bandwidth or –120dBC/Hz).
The performance degraded at the
lower frequencies and on 1.8MHz
was 9dB worse. These results are

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1.8MHz 95W -55dB -25dB -39dB

3.5MHz 97W -50dB -24dB -38dB
7MHz 100W -68dB -30dB -36dB
10MHz 99W -57dB -34dB -34dB
14MHz 99W -58dB -38dB -36dB
18MHz 100W -54dB -41dB -38dB
21MHz 106W -64dB -34dB -36dB
24MHz 986W -57dB -29dB -36dB
28MHz 102W -66dB -26dB -36dB
50MHz 98W -59dB -22dB -38dB

Intermodulation product levels are quoted with respect to PEP.
Sideband and carrier suppression: 60dB

Transmitter AF distortion: much less than 1%
Microphone input sensitivity: 0.2mV to 30mV for full output

NOTE: All signal input voltages given as PD across antenna
terminal. Unless stated otherwise, all measurements made on
USB with 2.1kHz bandwidth filter selected.

rather poor and some 5 to 9dB worse

than measured for the FLEX-5000A. I was
unable to measure intermodulation limited
dynamic range and third order intercept as
reciprocal mixing noise dominated and at
higher levels ADC overload occurred.
Similarly, blocking could not be measured
but I had the impression that the front-end
had good strong signal performance. Inband
distortion levels are extremely low and this
makes for a very clean sounding receiver.

Transmit intermodulation products on
SSB were generally reasonable on the middle
bands but poor on the low and high bands.
It is important to set the microphone gain
correctly. A helpful TX mic meter setting is
provided for this purpose. The CW keying
envelope was clean and well shaped with
negligible character shortening. A delay
of about 40ms resulted with my laptop, it
should be shorter with a faster PC. This
delay is about half of that measured with
the FLEX-5000A and an earlier version
of PowerSDR.

ON-THE-AIR PERFORMANCE. As might be

expected, the overall operating experience
was similar to the FLEX-5000A. I found
the on-air performance of the radio very
impressive. The receiver sounded very
clean and low noise. The audio quality is
excellent and the filter arrangements are
really effective. There is no click when the

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