Spectrum DSP M2 User Manual

Spectrum DSP M2 User Manual V1.1
If you choose a different, lower side-tone frequency note that you may sacrifice opposite
sideband rejection at higher frequencies, particularly if you null it at too-low a frequency! You
should carefully choose your "alternate" frequency as to provide a good compromise good
opposite sideband rejection at the desired frequency and higher frequencies (e.g. 750 Hz and
up).
Explanation of the “Frequency Translation” feature
PLEASE read the following VERY carefully!
Menu item “RX/TX Freq Xlate” selects the enabling/disabling of baseband frequency
translation in the receiver/transmitter. When the translation is active, instead of the receiver
operating at and around "DC", the signals are mathematically shifted from 12 kHz (above or
below – user-selectable). When frequency offset/translate is active, the [TUNE/O] button will
be shown in green.
Performing this frequency shift can help forgive a lot of the "sins" that occur with "DC"
conversions - the most obvious of which are that ANY noises in the power supply as well as
the 1/F noises of op amps, mixers, A/D converters and the like tend to show right up in the
received audio. With the signals at microvolt levels, minimizing these signals requires careful
design and earthing considertions!
•
• These signals/problems can show up as:
• Hum
• Buzzing with the dimming of the backlight
• Noises from the Waterfall SPI 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 12 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 and waterfall
display when “magnify” mode is turned off.
• RX LO LOW - In this mode the signals are shifted ABOVE zero Hz by 12 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 and
waterfall display when “magnify” mode is turned off.
Additional options may be added in the future.
P 63

Spectrum DSP M2 Specifications

General

Brand	Spectrum
Model	DSP M2
Category	Test Equipment
Language	English