Spectrum DSP M2 User Manual V1.1
• Buzzing with the dimming of the backlight
• Noises from the I2C communications (e.g. “ticking”)
It should be noted that these code modifications DO NOT relieve the builder of the strong
recommendation that one perform the modifications in the "Spectrum DSP Board
Modifications" file, particularly the U3a and MCU and LCD power supply modifications (for UI
board 0.3) but they should go a long way toward reducing the artifacts that can still occur
even after making those modifications - even to the point of gaining an extra S-unit or two in
sensitivity.
Menu item “RX/TX Freq Xlate” has the following options:
• OFF - This is the original operation of the transceiver with the receive (and transmit)
signals operating at and around zero Hz.
• RX LO HIGH - In this mode the signals are shifted BELOW zero Hz by 6 kHz, requiring
that the local oscillator be shifted up by the same amount. The received signals are
tuned at the first graticule left of center on the spectrum scope.
• RX LO LOW - In this mode the signals are shifted ABOVE zero Hz by 6 kHz, requiring
that the local oscillator be shifted down by the same amount. The received signals are
tuned at the first graticule right of center on the spectrum scope.
For various reasons (e.g. the use of USB on higher bands where the potential for zero-
HZ interference is highest) the use of “RX LO LOW” is recommended for best
performance!
Quirks and side-effects:
When the translate mode is activated and “magnify” mode is not turned on you will note that
the receive signal is no longer in the center of the spectrum scope! Along the bottom of
the spectrum scope you'll observe that the frequency display is changed, with the frequency
in kHz being displayed in full under the graticule, being shifted left or right as noted above.
If you have used other SDR software – particularly “sound card” SDR rigs on
computers – you will already be familiar with this sort of shift!
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