Selectivity improvement solutions proposal for UmTRX

Jean-Samuel Najnudel - BJT PARTNERS SARL jsn at
Sun Mar 18 17:23:33 UTC 2012

Hi Andrey,

What do you think about Alexander's suggestion ?
If we can find an affordable and convenient solution to connect to the
mezzanine board on the UmTRX, this would be great. It would allow us to
start the production of the first release of the UmTRX while we work on the
mezzanine board design.
If we do not have any other solution than using standard SMA connectors, it
would cost us quite a lot (connectors, balun, matching...) and it might be
a better solution to have the preselecter on the UmTRX PCB.
What do you think ?

On Sun, Mar 18, 2012 at 6:13 PM, Alexander Chemeris <
alexander.chemeris at> wrote:

> Hi Jean-Samuel and Andrey,
> On Sun, Mar 18, 2012 at 18:25, Jean-Samuel Najnudel - BJT PARTNERS
> SARL <jsn at> wrote:
> > However, I really believe the preselector should remain on the UmTRX main
> > PCB.
> > If we want to connect the preselector as an external mezzanine board, it
> > would cost us 5 extra SMA connectors (RX1in, RX1out, RX2in, RX2out, clock
> > source), 2 RF switches before the superhet filtering (to still be able to
> > have switched diversity), several GPIO (serial mixer control, RF switches
> > control) and power supply.
> > This is possible but it would really cost much more than keeping the
> > preselector on the main PCB, especially as I believe, in practice, we
> will
> > need almsot always this preselector, even not to pass the GSM spec but
> just
> > to be able to get a reasonably narrow sampling bandwidth.
> > I would really suggest to keep the preselector in the main PCB and
> > populating or not the components (VCO/PLL, mixer and SAW IF).
> Could we save on connectors if we use some RF side connector with many
> pins? Nothing specific in mind, just thinking out loud.
> --
> Regards,
> Alexander Chemeris.
> CEO, Fairwaves LLC / ООО УмРадио
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