Download The IC-7800

Introduction to the IC-7800.
6KHz. These filters reduce the probability that out-of-band signals and interference can pass into the DSP IF. The
15kHz filter is used in AM & FM modes; the 6kHz is used in all other modes. Little known to many is the fact that there
is a different set of filters in the transmit signal path. These are 20kHz and 4kHz, but don't think for a moment that this
means the radio transmits at that bandwidth. The code in the DSP system PSN (Phase-Shift-Network) for transmit will
not allow a bandwidth of more than 2.9kHz on SSB, and 6kHz on AM, as well as 15kHz for FM. There are no
modifications that can "open up" the transmitted occupied bandwidth (TOBW); it is all "hard-coded" into the DSP
software/firmware. The RX filters are fundamental-mode monolithic crystal type operating at the 1st IF level. The TX
filters are ceramic type, operating at 455kHz.
I wondered what the effect would be, between the two roofing filters. I set up a test to measure it, I set my signal
generator to act as a Broadcast transmitter with very wide interfering sidebands. Then measured the effect of switching
the roofing filters ( a menu selectable item, for each mode, except FM). I found that switching from 15kHz filter to the
6kHz reduced the interfering signal strength by 6dB. So, they do make a difference. If you receive interference, try the
narrow roofing filter.
(Roofing filters)
There are two separate AF amplifiers, one for the internal and external speaker, the other for the headphones. Both amps
are dual channel stereo type. This is an added expense usually found only in high-end military and commercial gear.
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