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
On Oct 2, 2007, at 7:53 PM, Duane - N9DG wrote:
>
> The RX-320 and the Pegasus/Jupiter are conceptually very
> similar, but there are some really quite significant
> differences circuit-wise.
>
> The RX-320's analog signal path is this:
>
> 1. Antenna.
> 2. Single fixed low pass filter (first IF rejection).
> 3. 1st mixer (pair J310's).
> 4. 45 MHz roofing filter.
> 5. BF998 gain stage
> 6. Diode ring 2nd mixer (MMSD914's).
> 7. 455 kHz filter.
> 8. 2x MMBT3904 gain stage.
> 9. Diode ring 3rd mixer (MMSD914's).
> 10 AD1847 CODEC.
>
> The Pegasus/Jupiter (probably) analog signal path is this
> (ignoring the TX items):
>
> 1. Antenna.
> 2. Band switched bandpass filters.
> 3. 1st mixer (pair J310's).
> 4. 45 MHz roofing filter.
> 5. BF998 gain stage
> 6. Diode ring 2nd mixer (BAT68_04's).
> 7. 455 kHz filter.
> 8. 2x MMBT3904 gain stage (with IF gain adjustment).
> 9. Diode ring 3rd mixer (MMSD914's).
> 10 AD1847 CODEC.
>
> Also the RX 320 has no provision for RF gain or attenuation
> in the signal path like the Pegasus/Jupiter do (which is
> really unfortunate). I find that to make the RX-320 truly
> listenable on 80M with a dipole during noisy summer band
> conditions I need put between 15 and 20 dB of attenuation in
> front of the antenna input. Once I do that it really is quite
> pleasant to listen to.
>
> Duane
> N9DG
>
>
> --- Kevin Purcell <kevinpurcell@pobox.com> wrote:
>
>> I really would have though the Jupiter would be better --
>> it probably
>> is in real life with better preselection/LPF. The
>> intercepts for the
>> RX320 are not very impressive.
>>
>> ARRL RX320 review:
>>
>> Minimum discernible signal (Noise floor), 500 Hz filter
>> Frequency
>> 1.0 MHz -117 dBm
>> 3.5 MHz -133 dBm
>> 14 MHz -134 dBm
>> Blocking dynamic range, 500 Hz filter
>> 3.5 MHz 111 dB*
>> 14 MHz 109 dB*
>> Two-tone, third order IMD dynamic range, 500 Hz filter
>> 3.5 MHz 84 dB*
>> 14 MHz 82 dB*
>> Third-order intercept
>> 3.5 MHz -7.4 dBm
>> 14 MHz -10.7 dBm
>> Second-order intercept
>> -29 dBm
>>
>> ARRL Jupiter review:
>>
>> SSB/CW sensitivity, 3 kHz bandwidth, 10 dB S/N: 0.35 μV.
>> Noise floor
>> (MDS), 525 Hz bandwidth:
>> 1.0 MHz −121 dBm
>> 3.5 MHz −127 dBm
>> 14 MHz −135 dBm
>> Blocking dynamic range: Not specified.
>> Blocking dynamic range, 525 Hz filter:
>> 3.5 MHz 113 dB
>> 14 MHz 123 dB*
>> Two-tone, third-order IMD dynamic range: Not specified.
>> Two-tone, third-order IMD dynamic range, 525 Hz filter:
>> 3.5 MHz 87 dB
>> 14 MHz 85 dB*
>> Third-order intercept: claimed +10 dBm.
>> 3.5 MHz +11 dBm
>> 14 MHz +7.3 dBm
>> Second-order intercept: Not specified.
>> Second-order intercept: +53.6 dBm.
>>
>> * == Measurement was noise-limited at the value indicated.
>>
>
>
>
>
> ______________________________________________________________________
> ______________
> Looking for a deal? Find great prices on flights and hotels with
> Yahoo! FareChase.
> http://farechase.yahoo.com/
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
--
73 DE N7WIM / G8UDP
Kevin Purcell
kevinpurcell@pobox.com
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|