[time-nuts] suggestions on getting 24 Mhz ?

jimlux jimlux at earthlink.net
Mon Apr 16 10:18:15 EDT 2018


On 4/16/18 3:45 AM, Pete Lancashire wrote:
> Access to " the xtal" is not an option the SDR is enclosed in a metal box.
> 
> Do a web search for RSP2Pro
> 
> 

It does have an external reference input..
There's not a lot of info on the Mirics data sheets (or on the sdrplay 
website)

It sort of looks like this is a somewhat enhanced version of the parts 
used in the RTL-SDR dongles.
(10 bit ADC, instead of 8 bits in the RTL2832)

And of course it needs 24MHz because it has to run the USB interface.

10 bit ADC means that you probably don't need *outstanding* clock 
performance - the sample and hold and all the other timing logic is 
probably designed to that sort of performance level - getting 
femtosecond jitter probably isn't worth it.


If you're just looking for a 24 MHz driver that doesn't need to be 
locked to anything, one of the SiTime modules would work, or you could 
probably order a TCXO for 24 MHz - it's a standard frequency (viz. USB), 
so it's almost certainly available from stock



> On Sun, Apr 15, 2018, 6:00 AM Attila Kinali <attila at kinali.ch> wrote:
> 
>> On Wed, 11 Apr 2018 03:00:23 -0700
>> Pete Lancashire <pete at petelancashire.com> wrote:
>>
>>> Needed for SDR project as external clock source.
>>
>> If your goal is, as Jim guessed, to get 24MHz from 10MHz and
>> you are using something like an RTL-SDR, then how about just
>> passing the 10MHz through a CMOS gate to square it up and
>> get nice harmonics, then pass a wire close to the crystal.
>> This should injection lock the crystal to right frequency.
>> It wont be a strong lock due to the 5:12 ratio, but for something
>> like a crystal that is already quite close, that should do the trick.
>>
>> Alternatively, using an ADF4002 with a small uC to configure it
>> and a VCXO/VCO should also work.
>>
>>                          Attila Kinali
>> --
>> <JaberWorky>    The bad part of Zurich is where the degenerates
>>                  throw DARK chocolate at you.
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