--- Kevin Purcell <kevinpurcell@pobox.com> wrote:
> The Jupiter has no preselection before the first mixer? Not
> even an octave or suboctave LPF in front of the first
> mixer?
I assume the Jupiter is like the Pegasus where the incoming
RX is routed throgh a diode switched set of filters
(octave?). The TX low pass filters are bypassed when in RX.
>
> The RX320 also relies on MMSD914 i.e. 1N914 PN switching
> diodes for
> both of its diode ring mixers too rather than the BAT68_04
> Schottky
> diodes the Jupiter uses in the second mixer. Though by the
> third
> mixer box are using the same diode (wouldn't the logic be
> if the
> second mixer use BAT68_04 then the third should to because
> you are
> worried about close in (455kHz filter bandwidth) IMD at
> that point.
> Why use it for the second mixer if you don't use it in the
> third? Or
> are they just resigned to it at that point.
I never got the sense that the limiting factor for this group
of radios has been the mixers themselves, it has always
seemed to me to be analog filter limitations. But admittedly
I have never tried to prove it one way or another.
> Does the Jupiter have several 455kHz filter bandwidth
> mechanical filters?
I'm sure it is just a ~15 kHZ wide ceramic (most likely)
filter at the 455 kHz IF, it is surely isn't mechanical.
There's just the one.
>
> Finally, how does the PLL differ on the Jupiter? The 80m
> IMD
> measurements are not noise limited (as they are on the
> RX320).
The same MC145140 PLL chip is used in the 320 as the Pegasus
(Jupiter too I presume). I think a very similar if not the
same PLL is used in the Elecraft K2. It's phase noise
behavior is largely determined by how it is configured. The
Jupiter was also notably better for phase noise than the
Pegasus per the ARRL tests. But I've also noticed that my
early S/N Pegasus does not have the tuning "tick" every 2.5
kHz like the newer S/N's ones do, or that has been reported
by Jupiter users. My speculation is that the PLL
configuration was tweaked slightly to improve phase noise
performance but in so doing introduced the "tick".
>
> BTW, how does this differ from the Paragon and Paragon II?
Only saw a Paragon schematic a few times, so I can't remember
the details too well. One big difference I do recall is that
the second IF is not at 455 like the 320/Pegasus/Jupiter/516
et. al. are.
Duane
N9DG
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