Selectivity improvement solutions proposal for UmTRX

Andrey Sviyazov andreysviyaz at gmail.com
Sun Mar 18 22:12:47 UTC 2012


Hi Jean-Samuel, Robin, Alexander and who interested too!

First of all, we discussing here not an mezzanine, so let we call it just
RF-board.

I still intend to make a separate RF-board on the following reasons:
1) Minimises of risk of a delay of the new UmTRX issue if I make some
mistake, especially if this will not fixable after manufacture. Redesign of
RF-board much easily and quickly in this a bit possible case.
2)  As it is rightly said Jean-Samuel, different boards of UmTRX for each
band would be very expensive and long to redesign. I think that the design
of a separate RF-board will take no more than two weeks, but for UmTRX not
less than month, because I'll forced to make the screening from the digital
part, and then checking the immunity against the digital noise and it is a
very difficult task.
3)  I plan to use for RF-board an simple and cheapest dual-layer FR-4-0.5mm
and this will reduce the cost  too, because of main UmTRX has six-layers
PCB and I will try to make the new UmTRX optimaly smallest.
4) On the RF-board, I plan to use inexpensive ceramic duplexers to save the
cost of the external (see attached datasheet). As I undersand, you do not
need any Down Link PA or some small (up to 100mW), so Tx-Rx isolation will
quite enough.
5) Regarding connectors, I only can suggest to use the two angle SMA-female
connectors for outputs which will stick out through the panel of the
housing (as you can use the angle SMA connectors, but for GPS and CLK_I/O
on the UmTRX board). At the same time for the internal 4 connectors we can
use some cheap like U.FL and cable assemblies U.FL-MCX or  U.FL-U.FL.
Signal CLK_26MHz,  6.5VDC, SPI and Switch controls will go via IDC control
connector.

Best regards,
Andrey Sviyazov.



18 марта 2012 г. 21:23 пользователь Jean-Samuel Najnudel - BJT PARTNERS
SARL <jsn at bjtpartners.com> написал:

> 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 gmail.com> wrote:
>
>> Hi Jean-Samuel and Andrey,
>>
>> On Sun, Mar 18, 2012 at 18:25, Jean-Samuel Najnudel - BJT PARTNERS
>> SARL <jsn at bjtpartners.com> 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
>> http://fairwaves.ru
>>
>
>
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