On Tue, 2007-10-02 at 23:21 -0700, Kevin Purcell wrote:
> I can't believe I misread the schematic and missed the first mixer. I
> looked over the circuit diagram (after messing with my Argosy and
> Omni 546C) and that left an impression that they must be using the
> diode ring as the first mixer. And the RF amp is only there for the E
> probe built-in antenna.
>
> Apologies for misleading the list before.
>
> The RX320 has no attenuator but that's not really to difficult to add
> (especially if you just need a manual switch).
>
> Adding preselection is a bit more complex (but I have a cunning plan
> on the list of things to do which could fix that). They did fix this
> in the RX321.
>
> But one question (as I've not seen or misread the Jupiter schematic
> before) ...
>
> The Jupiter has no preselection before the first mixer? Not even an
> octave or suboctave LPF in front of the first mixer?
>
> 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.
>
> Does the Jupiter have several 455kHz filter bandwidth mechanical
> filters?
>
> Finally, how does the PLL differ on the Jupiter? The 80m IMD
> measurements are not noise limited (as they are on the RX320).
>
> BTW, how does this differ from the Paragon and Paragon II?
>
> Curious minds, etc.
>
> Thanks
> Kevin
>
I'd rather see them spend $3.95 on a packaged mixer made by an expert in
mixer making than spend 2 cents on slightly slow diodes and 23 cents
each on almost good enough transformers. I think the receiver
performance would be detectably better with the packaged mixer, like a
MCL TUF-1H... though the H suffix may cost a little more than $3.95, its
not much.
73, Jerry, K0CQ
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