Filtering of the Icom IC-775DSP
I like "wide" bandwidth SSB,
so I changed the standard 9 MHz Icom FL-80 filter (2400 Hz bandwidth)
with the Icom FL-70 filter (2800 Hz bandwidth).
Note: after replacing the FL-80 with the FL-70
I got much better audio reports!!
The transmitter of the IC-775DSP is using this filter for its audio,
but you have to switch COMP = ON.
When the compressor is off, the filter is bypassed.
With the DSP (PSN-t) = OFF, the filter is always in.
The standard Icom FL-80 9 MHz IF-filter with 2.4 kHz bandwidth.
Always use the right screwdrivers which will fit the screws of your rig.
Any other screwdriver will permanently damage the screws.
Be aware of failures caused by ESD! Never wear clothes like Fleeze while doing this job.
ONLY pull out the four flatcables from the IF-board. This is very easy.
Don't remove any other cable!
Just move the other cables a bit upwards, in order to remove the IF-board more easily.
Remove the screws.
Carefully lift the IF-board and turn it very gently over.
Be careful not to damage any part or cable.
De-solder the FL-80 IF-filter.
I use thin de-soldering braid (litze), size 075 from Chemtronics.
Change the FL-80 with the FL-70 IF-filter. Be careful to use the right IN- and OUTPUT!
Afterwards I installed the Icom FL-44A 2400 Hz filter.
Installed 9 MHz IF-filters
FL-102: 6 kHz
FL-70: 2800 Hz
FL-223: 1900 Hz
FL-32A: 500 Hz
FL-232: 350 Hz
Installed 455 kHz IF-filters
FL-96: 2800 Hz
FL-44A: 2400 kHz
FL-52: 500 Hz
FL-53: 250 Hz
This will give the following front-controlled filter selections on SSB:
WIDE ON - 9 MHz NAR OFF - 455 kHz NAR OFF: 6 kHz bandwidth (very wide)
WIDE OFF - 9 MHz NAR OFF - 455 kHz NAR OFF: 2.8 kHz bandwidth (wide)
WIDE OFF - 9 MHz NAR OFF - 455 kHz NAR ON: 2.4 kHz bandwidth (medium)
WIDE OFF - 9 MHz NAR ON - 455 kHz NAR OFF: 1.9 kHz bandwidth (narrow)
Other combinations are possible too (e.g. on SSB):
WIDE ON - 9 MHz NAR OFF - 455 kHz NAR ON: cascaded 6 and 2.4 kHz bandwidth (wide/medium)
WIDE ON - 9 MHz NAR ON - 455 kHz NAR OFF: cascaded 6 and 1.9 kHz bandwidth (wide/medium)
WIDE ON - 9 MHz NAR ON - 455 kHz NAR ON: cascaded 6, 1.9 and 2.4 kHz bandwidth (medium)
WIDE OFF - 9 MHz NAR ON - 455 kHz NAR ON: cascaded 1.9 and 2.4 kHz bandwidth (medium/narrow)
Note: the above selections will give different results on CW/RTTY, AM and FM.