I have a question about the design of 2nd mixer in the IC-7800.
From : http://www.icom.co.jp/world/products...7800/index.htm
man could see that Icom use an oscillator with outputs in quadrature and
then sum the mixer outputs after a 90° phase shifter.

What I don't understand , is why do they do the 90° phase shift in the
analog domain ?
Using 2 mixers with a quadrature oscillator is very common in the DSP
world (IQ demodulation). But in general , it's followed by 2 A/D
converters and if phase shift is needed to reject a side band, it's done
digitaly...
I don't think that Icom choose this design just to save an A/D in the
IC-7800 ....

any clues ?

Thierry
F4DWV