IC-775 / dsp
1 - Remove power and antenna.
2 - Remove screws and open the
3 - Locate logic board
[ Board B42918 ]
4 - Remove jumper chip W1.
5 - Reassemble the radio.
6 - Reset the microprocessor if
( Press [ CLEAR ] and turn the power ON. )
Modifications for the Icom IC-775
|New product information IC-775DSP
Icom's new superior class HF transceiver the IC-775DSP is designed
as a successor to the IC765.
The IC775DSP offers high quality receive and transmit audio for
In addition, a non-DSP type, the IC775, is also available.
DSP (Digital Signal Processing; DSP-type only)
DSP digitally transposes transmit and receive audio signals to
produce desired AF frequency characteristics and in addition
performs the following functions:
- Noise reduction - DSP converts all
analog audio components to digital components, then separates
them into voice and noise at the digital stage. In this way,
voice components can be singled out and demodulated back to
analog signals so that weak signals that would normally be
drowned out by noise are audible. The reduction level can be
adjusted to obtain the most desired audio characteristics.
- PSN modulation - PSN method (Phase
Shift Network) generates SSB signals directly without DSB
signals or SSB filters. Therefore even audio characteristics,
over the entire range from low to high audio components, can be
obtained, as well as high quality audio without filter group
- Automatic notch filter - automatically
suppresses the highest level beat signals in the audio
- Twin PBT - One of the more highly
praised functions of the IC-781 - twin PBT narrows the IF-pass
band in two stages to efficiently eliminate interfering signals.
This function is especially useful during crowded band
conditions such as pileups, contests, or for nets, etc.
- IF Notch - The IC-775's notch filter
functions at the IF stage, therefore, sharp and deep filter
characteristics are obtained as with the IC-781.
- Automatic Notch (DSP-type only) - An
automatic frequency adjusting notch filter ia available at the
AF stage separate from the IF notch. This automatic notch
reduces the maximum beat level with no manual adjustment
- APF (Audio Peak Filter) - Allows a
particular frequency to pass through at the AF stages. This
function is convenient for CW operation. In addition, CW pitch
is also related changed with APF.
- Dual Watch Functions
Dual watch monitors 2 frequencies on the same band
simultaneously. Ideal for contests, traffic handling, DX chasing
and net control work. To operate the dual watch, the IC-775 has
two PLLs, two RF circuits and a balance control to balance
- Twin Tuning Knobs
For convenient dual watch operation, the transceiver has two
tuning knobs. The large main knob has good tension and response;
the small, independent sub small knob can be used to watch a sub
- Newly designed PLL
A new design is employed in the PLL circuit using ICOM's DDS
technology and removing mixer circuits, resulting in higher
quality C/N characteristics and superior spurious rejection.
- Power MOS FET's for clean signal.
Superior 3rd, 5th, 7th IMD characteristics are blamed by power
MOS FET's with high voltage. The IC-775 employs power MOS FETs
in the pre-driver, driver and final amplifier stages, providing
a clean 200 W of output over all bands.
GREAT FUNCTIONS FOR CW OPERATIONS
- Memory Keyer - This function is
convenient for contest, etc. an often-used word or phrase can be
programmed, such as a callsign, "CQCQ", etc
- Electronic Keyer - Newly designed
electronic Keyer. Weight control can be adjusted using set mode.
- CW Pitch Control - Adjusts the audio
pitch of any CW signal without changing the operation frequency.
- CW Reverse - CW carrier point can be
selected on USB and LSB bandwidth while receiving CW to reduce
- Two key jacks - The transceiver has a
total of two key jacks on the front and rear panels. The front
panel key jack accepts a paddle and a straight key (selectable
using set mode) and the rear panel jack accepts a straight key
or an external memory Keyer.
- Full break-in (QSK) capability
- Variety of filters selectable 3
selectable filters are available to achieve a desired bandwidth:
Mode Wide Middle Narrow
CW 2,4kHz 500Hz 250Hz (option)
SSB 6,0kHz 2,4kHz 1,8kHz (optional)
- OTHER FEATURES
1 crystal control for high frequency stability
Large heat sink and cooling fan
Selectable tone/shift frequency from set mode for instant data (AFSK)
2 selectable preamplifier gain (18-28MHz only)
CFL (Cold cathode Fluorescent Lamp) back light for large LCD
Two antenna connectors with automatic selector.
High speed automatic antenna tuner.
Level/width variable noise blanker.
Gain selectable preamplifier (2 positions)
SWR/Po/ALC/COMP/Id/Vd selectable large analog meter
Improved quick split function
Convenient memo pad function
Transmit signal monitor
Double band stacking register
Built-in heavy duty power supply
RF speech compressor
IC-775DSP Out of Band Information
- Remove front panel to locate the main
- Remove W1 chip jumper located next to R111
on the main unit.
- Re-install front panel.
- Push clear and turn on rig (CPU reset).
sensitivity on MW-band 0.5-1.6MHz on IC-775 and IC-775DSP
Author: SM4RNA Anders
At the input at the band pass filter on RF-Unit for MW, 0.5 to
1.6MHz, a 10dB attenuator is located. This attenuator also is a
current limiter for the diode D19.
By removing the attenuators three
resistors and lead the diode current thru a inductor instead, the
increased sensitivity is achieved. But important is to limit the
current by changing the value on R119.
To do the mod:
- R116 is exchanged with an inductor of
- R117 removed and shorted.
- R118 is removed.
- R119 is exchanged with 150 Ohm
All resistors are surface mount.
The result is that the sensitivity is
increased in the 0.5 to 1.6 MHz range is changed from -103dBm to
-112dBm at 12 dB SINAD, 70% AM.
My personal findings are that this do MW
listening much more interesting and enjoyable and I have no
problems with to strong signal distortion what so ever.