--- In [email protected], "jabauzit" <[EMAIL PROTECTED]> wrote:
>
> --- In [email protected], "joe price" <joeprice@> wrote:
> >
> > .................. Whe using one of Tony's Softrock5 receiver boards
> > as a test bed I notice that the image balance will change with bands
> > and OSD input tuning (i'm using a preselector). .............
> >
> > Joe wa9cgz
> >
>
> When changing antenna on a SoftRock the I/Q balance will change and
> may be it is what you are experiencing as you change what is ahead of
> the SoftRock. You could test it by using a signal generator going to
> the SoftRock thru a 50 Ohms attenuator and see if the balance changes.
> If it does not - or very little - you could add a preamp ahead of the
> preselector and a 50 ohms attenuator between the preselector and the
> SoftRock. For example a J310 preamp with a 10dB gain and a 6 dB
> attenuator, with the loss of the preselector the total gain would be
> close to 0dB but the QSD would see a constant impendance.
>
> Jean-Claude PJ2BVU
>
Using the 9854 I found that a Norton Noiseless Feedback amp, which has
a nice well defined (very close to) 50 ohm wideband impedance, with a
9.5 db gain is beneficial in 'pushing down' the level of the DDS spurs
in the output of the QSD (The SDR-1000 does this too but IMHO went too
far with a 20 db preamp, also running an INA mic preamp IC at less
than 40db gain is not good and running it at unity gain is a big
mistake) ... of course you lose some IP3 but high speed buss switch
based QSD's have plenty to spare so it's still better than most rigs
out there ... I'm hoping that with the new dual 9952 circuit I'm
working on will allow me to drop the preamp except when necessary on
the upper bands or with loop and other low gain antennas
JR
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