Phil wrote, in part:
> 6) Rohde & Schwarz may have taught ICOM some tricks...
If no more than how to feed attenuation back to the front
end to increase IP at the expense of MDS, not really
worth much to the serious contest or DX operator.
Add 10 dB of attenuation; IP3 goes up 20 dB!!
Those fellows want to hear signals right down near the
noise level of their radio's full sensitivity. The way R&S
increased the IP3 number is to add attenuation up front;
and there goes the sensitivity, obviously. Works great
for government purposes, but not useful most of the
time to amateur operators.
For details on the R&S design, which Icom has evidently
licensed from them, see Ulrich Rhode's article in the
Jan/Feb 2003, QEX; specifically the block diagram at
the bottom of page 28, his Fig. 43, and the text at the
top of the next page, "Because the AGC now makes heavy
use of a pre-attenuator, which operates quasi-continuously,
the intercept point now depends on he amount of pre-
attenuation." !!!?? Evidently this is a block diagram of
the R&S XK2100L and EK895, both of which he goes
on to discuss on the following two pages along with
his measured performance data.
IF this is the technology which Icom has licensed from
R&S, and so used in this coming new IC-7800, I
am in NO WAY interested; just does NOT apply
to my operating, hi. I want "instantaneous" high
IP and the lowest possible MDS as limited only
by the phase noise of the rigs oscillator sources.
I can control the same thing Ulrich writes about using
the Orion 6, 12, or 18 dB manual attenuator button, along
with the RF gain control and the ability to turn the preamp
on/off. I do not want "quasi-continuous" attenuation in
my rig's signal path, hi.
73, Jim KH7M
|