Re: [Openbts-discuss] [Discuss-gnuradio] New external clock board for USRP

[Alexander C. <ale...@gm...>]

David,

Do you have any specific VCTCXO model in mind?

On Tue, Sep 29, 2009 at 22:16, David Burgess <dbu...@ke...> wrote:
> We expect to be able to get VCTCXOs in modest volumes for less than $30.
>  The TCXO we are using now is $23.  Most of the cost of the clock doubler
> board is the labor for getting it assembled locally in small batches.
>
> When/if the FPGA firmware gets fixed, we can use a 26 MHz part without a
> doubler, which would reduce the cost further.
>
> -- David
>
>
> On Sep 29, 2009, at 2:02 AM, Alexander Chemeris wrote:
>
>> Hi David,
>>
>> Could you elaborate why do you consider this approach? While we see some
>> advantages of it in terms of lower noise, it looks like our approach
>> is few times
>> cheaper with reasonable noise and stability figure. If we understood
>> correctly,
>> bare VCTCXO chip costs $230 on DigiKey, while in our case discrete unit
>> with
>> all accessories produced in low volume costs about $100.
>>
>> On Mon, Sep 28, 2009 at 22:06, David Burgess <dbu...@ke...>
>> wrote:
>>>
>>> One of the approaches we are considering for OpenBTS is to use a VCTCXO
>>> with
>>> the control voltage taken from one of the D/A outputs of the FPGA, with
>>> LOTS
>>> of low-pass filtering, of course.
>>> This would not give a wide range of frequencies, but would allow precise
>>> frequency calibration through the existing libusrp APIs.
>>>
>>> On Sep 28, 2009, at 9:00 AM, Tim Pearce wrote:
>>>
>>> In terms of integrating more tightly with the USRP/GnuRadio
>>>
>>> You could (maybe) just use the SPI pins and one of the digital IO lines
>>> as
>>> the enable (the ATMega8 running as a slave)
>>>
>>> That way theres functions to communicate with the chip already built in
>>> you
>>> just need to define the various commands etc?
>>>
>>> Tim.
>>>
>>>
>>> David A. Burgess
>>> Kestrel Signal Processing, Inc.
>>>
>>>
>>>
>>>
>>
>>
>>
>> --
>> Regards,
>> Alexander Chemeris.
>>
>> SIPez LLC.
>> SIP VoIP, IM and Presence Consulting
>> http://www.SIPez.com
>> tel: +1 (617) 273-4000
>
>
> David A. Burgess
> Kestrel Signal Processing, Inc.
>
>
>
>
>



-- 
Regards,
Alexander Chemeris.

SIPez LLC.
SIP VoIP, IM and Presence Consulting
http://www.SIPez.com
tel: +1 (617) 273-4000