From October 2009 QST © ARRL
volume can increase dramatically.
Modes
In the MODE box you can select upper
and lower sideband (for phone, CW or digi-
tal operation), double sideband phone, AM,
synchronous AM, narrow FM or full spec-
trum mode. Digital Radio Mondiale (DRM)
requires a separate software demodulator
application.
The
MODE SPECIFIC CONTROLS
box
provides access to a variety of adjustments
for CW, phone or digital modes. Depending
upon what mode you select, the specific
adjustments in the box will change.
For voice modes, the FLEX-3000 has slid-
ers for mic gain, speech compression, VOX
and a noise gate control. The noise gate is a
kind of digital squelch for audio. Say you
have a noisy fan in your shack. Adjust it to
the fan’s noise level and only sounds louder
than the fan will be transmitted. Note that
this is separate from the VOX function. The
TRANSMIT PROFILE is a stacking memory
that contains settings relevant to transmitter
output settings (microphone gain, compres-
sor level, transmit filter, etc). You can use the
supplied profiles or create your own. Finally
the phone mode specific controls box has a
button to access equalizers for both receive
and transmit audio. The VAC button activates
the Virtual Audio Cable, which is a third
party program used for digital modes.
In the CW box you will find controls to
adjust the internal CW keyer speed (1-60
WPM), select iambic or straight key, adjust
break in delay (10 ms minimum), set the
tone, control the monitor and even indicate
the transmit frequency on the display.
When a digital mode is selected you have
controls for adjusting receive and transmit
gain, sampling rate and mono/stereo control.
The digital mode control is primarily de-
signed to operate using the VAC to interface
with third party software.
Filters
Our current uncooperative sun has caused
a lot of activity to be pushed down below the
15 meter band. Things can get very crowded
on 20 or 40 meters these days and a good set
of filters is invaluable in separating the DX
from the local ragchew. The FLEX-3000 has
10 mode dependent filters and two variable
filters that give you a large amount of control
over what gets through your IF.
Each mode has a preset collection of fixed
filter widths. The fixed CW filters run from
25 Hz to 1 kHz, the fixed SSB/digital filters
run from 1 to 5 kHz and the fixed DSB/FM/
AM filters run from 2.4 to 16 kHz. These
filters come preset by the factory but, as with
just about everything on the ’3000, the values
are adjustable.
There are also two variable filters avail-
able in each mode group. The maximum and
New Product Review Tests
You may notice a few extra lines in the Product Review data (Table 1) this
month. Here at the ARRL Lab we strive to make our test procedures relevant
to current technology and to new features common on today’s transceivers. We
continue to research ways to improve our testing and to develop new tests that
will benefit our members.
Receiver Sensitivity (MDS) at 137 and 505 kHz
Several countries now give amateurs permission to operate at and around
137 and 505 kHz. In the US, there is activity on 495 to 510 kHz by more than
20 stations around the country operating under the ARRL sponsored WD2XSH
experimental license. In addition, there are other Part 15 experimental licensees
operating in this range. The WD2XSH stations are on the air regularly, gathering
propagation data. They are always looking for signal reports. To read more about
these and several other experimental stations, check out www.500kc.com.
With many of today’s transceivers and a suitable antenna, you can listen for
these experimental stations and submit reception reports via the Web site. The
new Product Review tests will help identify transceivers suitable for use on these
frequencies. With equipment built over the last 25 years ago or so, I’ve noticed
a wide variety of available sensitivity, from terrible to quite good. Many receivers
tune to 137 and 505 kHz; not all are proficient at receiving signals there. For you
“lowfers,” this measurement is for you.
Spectral Sensitivity
Spectral sensitivity is the weakest signal that can be “seen” on a visual dis-
play of spectrum above and below the operating frequency. Often called a spec-
trum scope or panadapter, this feature is included on many of today’s mid-range
and high-end transceivers. This data represents the level, in dBm, at which the
operator can see a signal poke up out of the display noise floor. Although the
measurement is somewhat subjective, it works out to be about 3 dB above the
noise floor at the bottom of the display when the scope is adjusted to show
100 kHz of spectrum. With SDR receivers, such as the FLEX-3000, the sample
rate is set to the highest setting.
Audio Output THD at 1 V RMS
One of our technical advisors has asked, “Who ever listens to their receiver
at full volume?” We have tested and reported audio output power and THD (total
harmonic distortion) at the specified load impedances as specified by the manu-
facturer. Generally the specification is at or near the maximum audio output the
receiver is capable of. If severe hearing loss isn’t an issue, we normally listen
with the VOLUME control set to around the 9 o’clock to 11 o’clock position on
most transceivers and not with the control cranked to maximum.
Distortion at normal listening levels is an important factor, especially when
you are listening for an extended period of time. High levels of distortion can
make signals more difficult to understand and add to fatigue. We’ll continue to
measure and report how audio output power and THD compare to manufac-
turer’s specifications, but we have added a new test intended to show distortion
at more typical volume levels.
After testing several radios for comfort, I picked 1 V RMS as an output level
for the new test. It’s an easy figure to remember. We will now also report THD
at this level. Note that this test will appear with the next transceiver reviewed
because the FLEX-3000 has only a low-level audio output and is dependent on
external, user-supplied devices to amplify the audio to normal listening levels.
I hope you will find these new measurements useful in evaluating and com-
paring transceivers. — Bob Allison, WB1GCM, ARRL Test Engineer
minimum sizes for these variable filters are
also configurable. In use, you can change the
width of the variable filters using either the
LOW or HIGH up/down boxes or the WIDTH
slider. The LOW and HIGH boxes permit
the adjustment of the individual edges of
the filter while WIDTH affects both edges
simultaneously. The SHIFT slider moves the
filter’s center frequency with respect to the
VFO frequency. Variable filter settings are
saved until changed.
In PANADAPTER mode you can also use
the mouse to drag the receive filters along the
frequency axis of the display to align it with a
signal and also to vary the width of the filter
by dragging its edges. Very handy.
DSP Noise Control
The ’3000 has four available digital signal
processing (DSP) noise reduction functions:
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