Weak Signal Dx Reception And Contest Operation And The Orion - Ten-Tec Orion 565 Manual

The ORION is now set up for diversity
reception with the main receiver and
transmitter on ANT 1 and the subreceiver on
ANT 2.
For low band DXing, it may be desirable to
combine the outputs of the two receivers
from two different receive antennas while
having the transmitter use a third antenna.
This is accomplished by connecting receive-
only antennas to both ANT 2 and the RX
ANT jacks on the rear panel, and using ANT
1 for transmitting.
Put the subreceiver on ANT 2, the main
receiver on RX ANT and the transmitter on
ANT 1 by pushing buttons on the front panel
so they light up as shown in Figure 4-9.
Again put both receivers and the transmitter
on VFO A.
Figure 4-9. Diversity reception. Main
receiver on VFO A is using RX ANT jack.
Transmitter on VFO A is using ANT 1.
Sub receiver on VFO B uses a second
receive antenna connected to ANT 2.
Using this configuration, both receivers can
use independent receive antennas while the
transmitter uses a separate TX antenna, all
on the same frequency. Both receivers are
tuned simultaneously by turning the VFO A
main tuning knob.
WEAK SIGNAL DX RECEPTION,
CONTEST OPERATION AND THE ORION
With recent transceivers, an operator
typically would set CW for a low or
comfortable offset, select a narrow
bandwidth filter (like 250 Hz), turn AGC to
either "fast" or "off", use some setting for
DSP noise reduction and start listening for
weak signals. Which is fine – except that
"typical" settings like this used for other
565 manual
Part #74279
Printed in USA
radios simply won't use Orion to its
maximum capabilities.
An important point to ponder: There is no
one setting for RX combination (defined
as roofing filter, DSP bandwidth filter,
DSP NR, and AGC together) that is the
correct one for Orion. There are good
places to start – and by understanding how
the operation of the high dynamic range
receiver in Orion is different from other
transceivers will set you on the correct path
toward optimum use.
Think this through logically. Band conditions
always vary, noise always varies, signals
always vary. If you set a transceiver for one
optimal setting to use it for variable
conditions, would it seem logical that the
operator would be using the transceiver to
its optimum capability each and every time?
Refer back to the above definition of the use
of a crystal roofing filter. The roofing filter is
used for keeping strong closeby signals from
compromising receiver performance.
Listening to a weak signal on a quiet band
does not meet the definition of need for a
tight roofing filter. On a band where few
signals are present other than a desired
target weak signal, only a wide roofing filter
would be necessary. Putting in the 250 Hz
roofing filter when listening to a single weak
signal on the low bands gains nothing
additional. In fact, it could hurt your ability to
hear a noise floor level weak signal. Why?
Among other reasons, all narrow bandwidth
filters suffer from insertion loss – and in the
Orion, like other transceivers have for many
years, we use an amplifier to compensate
for crystal filter loss. A 250-Hz filter is going
to have slightly more loss than a 500-Hz
filter. Both of these narrow filters have
more loss than the 1 kHz roofing filter. The
loss, after preamp compensation, is about 2
dB. No loud signals nearby = no need for
a tight roofing filter. Regardless of DSP
bandpass filter setting, we'd recommend
using a wider roofing filter as acceptable for
weak signal DXing. The DSP bandpass
filtering does not vary in gain down to the
minimum setting of 100 Hz. Therefore, if
there is no offending signal within 1 kHz,
setting the roofing filter at 1 kHz and
narrowing the DSP bandwidth to any desired
value is by far the best setup for Orion for
single signal DXing.
September 2003
44