[time-nuts] Using cheap sound cards for measurements

[Bruce Griffiths]

Not the least of which is ensuring that the oscillator output can
actually drive the coax  satisfactorily.
The effect of reflections due to the unterminated coax may be
significant unless the oscillator output is matched to the cable.

Bruce

John Miles wrote:
> That particular method is vulnerable to a lot of things. :-P
>
> -- john, KE5FX
>
>   
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>> Behalf Of Bruce Griffiths
>> Sent: Friday, August 21, 2009 2:20 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Using cheap sound cards for measurements
>>
>>
>> That particular method is vulnerable to RF pickup from within the PC.
>> The coax screen should be RF grounded at both ends.
>>
>> Bruce
>>
>> Christian Vogel wrote:
>>     
>>> Hi Lux,
>>>       
>>>> Syncing inexpensive cards is a real chore (and the only reason to be
>>>> thinking about using this in the first place is to keep the cost to a
>>>> minimum, otherwise, you might as well build a special purpose little
>>>> box with counters & A/Ds, and an interface)
>>>>         
>>> I've had too many problems with cheap (onboard) soundcards in the
>>> past, even when using them for their intended purpose, so I would not
>>> advice to use them for anything quantitative.
>>>
>>> But if you *really* want to syncronize inexpensive soundcards, it's
>>> rather trivial, see for example
>>>   http://quicktoots.linuxaudio.org/toots/el-cheapo/ .
>>>
>>> Just buy a few dozens for a EUR/$ each and hunt down the ones with
>>> identical oscillator frequencies ;-). But don't expect miracles, you
>>> end up with a few synchronized cards that only happen to not skip
>>> samples with respect to each other. Compared to decent signal input
>>> they are still cheap cards, and hog the CPU for their individual
>>> servicing.
>>>
>>>    Chris
>>>       
>
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