Compaq FLEX-5000A - Manual (Page 5)

From July 2008 QST © ARRL
Figure 5 — You can split the PowerSDR screen to show any
combination of the panadapter and waterfall displays. Figure 6 — PowerSDR offers 3 or 10 band graphic equalizers for
both receive and transmit.
dow and seemed tacked on as an afterthought
(or maybe they just ran out of space). I liked
the combination panadapter/waterfall display,
since the waterfall sometimes shows signals
not readily visible on the spectrum scope.
Manually tuning with the cursor works
like this: Hold down the left button and the
cursor becomes a little hand. Then swipe the
“hand” across the display horizontally in the
desired direction. But there’s the rub. I had
to swipe in the opposite direction, or sense,
from what my aging brain expected. To move
up the band, you swipe from right to left,
whereas on a conventional transceiver you’d
turn the knob from left to right (clockwise).
It’s logical when you think about it (mov-
ing from a lower frequency to the left to a
higher one to the right), and I eventually got
the hang of it.
If you don’t like swiping/sliding to tune,
the little mouse scroll wheel does the job
quite nicely. This made better sense to my
brain too. You scroll up to move up in fre-
quency, down to move down.
You can use the cursor not only to tune
but to shift the receive passband and change
its bandwidth. FlexRadio calls this feature
“FilterSlide.” It works very well for custom
filtering on the fly, although the preset filters
suffice under most circumstances. Filters are
not mode-specific and you can winnow the
passband down to a lean 25 Hz assuming
adequate sampling rate and buffers. You can
click and drag the
VFO B passband anywhere
on the visible display — above or below your
operating frequency.
PowerSDR also lets you control vari-
ous radio functions, including tuning, band
switching, mode, filter and RIT/XIT via the
keyboard. This includes the ability to directly
enter a frequency.
For less pointing and clicking, an optional
ShuttlePRO controller is available through
FlexRadio. This mouse-like device has 15 pro-
grammable buttons and two concentric tuning/
control knobs that you can set up for VFO tun-
ing, RIT, filter width, mode and other often-
used functions. The optional Griffin Power
Mate VFO control knob is also available if
you find you can’t live without a knob.
Of Buffers and Sampling Rates
The various buffer and sampling rate
settings significantly affect how — and how
well
— the FLEX-5000A functions. Reach-
ing equilibrium can be a chore. First you need
to set the sampling rate and buffer size for
the FLEX-5000A driver, which determines
the data rate and buffer size for the FlexWire
interface. Once inside PowerSDR, you enter
the same sampling rate and buffer size under
the Setup menu
AUDIO tab and set buffers for
transmit (TX) and receive (RX) under the
DSP tab. These DSP buffer settings signifi-
cantly impact filter shaping and latency.
FlexRadio suggests setting the driver and
the audio buffers as low as the associated
computer’s processor can handle (lower buf-
fer settings shift the workload to the proces-
sor with less latency or delay but broader
filter skirts). The “Buffers and Sample Rate”
appendix of the Owner’s Manual advises
avoiding a buffer size of 512 for SSB opera-
tion “except for casual QSOs and then only
at sample rates of 48 kHz and 96 kHz.” For
those situations where you need steep filters,
however, the manual suggests buffer sizes
of 2048 or 4096. It’s a bit different for CW
and digital operation. For these FlexRadio
recommends steering clear of buffers of 512
and 1024 and using “only the sample rate
of 48 kHz.” FlexRadio says that some of
these suggested settings are in error and has
revised the instructions for proper selection
of buffer size.
Operating with our second computer
(see sidebar, “Switching Computers Mid-
stream”) and using a 192 kHz sampling rate,
the FLEX-5000A was more prone to audio
dropout — essentially “holes” in the audio —
especially when you’re working in one of the
menus, enabling other radio features such as
MULTIRX or using (not just running) another
program on the same PC. Lowering the RX
buffer seemed to cure this. I went through
2048 to 1024, experiencing far less dropout
at the latter and even lower settings.
There’s a tradeoff, however. Reducing the
size of the RX buffer alters the filters’ skirt
shape and makes them less effective — “roll-
off” filters as opposed to “brick-wall” filters.
With a too small buffer you’ll find essentially
no change in the actual passband below a
certain filter selection, depending on mode.
On the other hand, latency — a minute but
finite lag between the time you key the PTT
and the RF signal appears — gets closer to
real time with smaller driver and audio tab
buffer sizes; the DSP TX buffer also has
an effect, however. In short, getting it just right
for a particular mode can be a juggling act.
Big and Beautiful SSB
Simply put, this radio can generate a
remarkable SSB signal. Within legal limita-
tions your ability to tailor the radio’s audio
characteristics is extensive. The panadapter
displays your SSB/phone waveform, so you
can see what’s going on. The compander —
something not found on most transceivers —
yields bigger, louder audio while not being
obnoxious. It is possible to engage both the
compressor and the compander, but you’ll
want to avoid extreme settings. Less is more
in this case. Stations I worked told me the
DX
button, which is new with PowerSDR v 1.10.4,
added another S unit or so to my signal. How
cool is that?
Switching in my headset’s DX
mic element augmented the effect.
The radio also has a “leveler” — a sort
of AGC to compensate for times when the
operator changes position with respect to the
microphone. A
NOISE GATE is available to
handle high background noise situations; it
operates independently of VOX.