Re: [Openbts-discuss] Kurtis Heimerl, Community Manager

[David B. <da...@ra...>]

Alexander -

It turns out that we don't have an electronic copy of the design drawings, so I'll just describe it here.

There are 12 MultiTech USB GPRS modems on a 12-port USB hub.  The RF connections of the 12 modems are tied together in a 12-port splitter with the output connected to the BTS unit.  There is about -40 dB leakage between ports on the splitter and we put 60 dB pad on every modem to give 160 dB of isolation between modems.  We put an additional 60 dB pad and 0-60 dB adjustable attenuator on the output of the splitter to simulate 120-180 dB of path loss between the modems and the BTS unit.

-- David



On Nov 2, 2011, at 1:02 PM, Alexander Chemeris wrote:

> Hi David,
> 
> We're thinking about a similar system. Thus I'd love to see your
> design. When we get it here I'll be happy to contribute something
> back.
> 
> On Wed, Nov 2, 2011 at 15:15, David Burgess <da...@ra...> wrote:
>> Kurtis -
>> 
>> We are building a test fixture from 12 MultiTech GSM/GPRS modems and bunch of RF cabling and a big USB hub.  We plan to use it for continuous testing.  The hardware is done.  We just need a server set up to run it and some scripts to drive it and collect the results.  If you are interested in helping on that, let me know.  If anyone else wants to build one of these, we'll be glad to share the design, but from an engineering standpoint there's not much to it, just a lot of fairly expensive parts.  (If you want to see it the next time you are at Brannan St, just ask John downstairs.)
>> 
>> -- David
>> 
>> 

David A. Burgess
Founder, CEO
Range Networks, Inc.
560 Brannan St.
San Francisco, CA 94107
USA
cell +1 707 208 2622