[time-nuts] Wavecrest DTS-2077 Teardown

[Ed Palmer]

Hi Said,

Yes, I saw your message from 2009 where you warned about the sine 
waves.  That's why I was watching for it.  Thanks for the warning.  I 
also realized that a DC Block and a 10 db attenuator makes a very nice 
TTL or CMOS to Wavecrest converter for anything except 1 PPS which would 
need about 15 db.  I tried an old circuit that uses an MC10116 ecl line 
receiver - it's actually a dead Racal Dana 1992 counter where I'm using 
the processing on the external reference input to square up the signal.  
It gives me a slew rate equivalent to about a 50 MHz sine wave.  It 
helped a lot, but not enough.  I'll try a 74AC04 and a BRS2G 
Differential Line Receiver (risetime < 3ns, 400Mbps throughput).  Both 
are in my junkbox.

Ed


On 8/20/2013 8:12 PM, Said Jackson wrote:
> Guys,
>
> The dts needs to be driven by square waves, driving them with sine waves gives jitter values that are displayed significantly too high due to trigger noise.
>
> Holzworth makes a small sine wave to square wave converter that can drive 50 ohms. Use a DC block and an attenuator on the cmos output to avoid damaging the dts inputs. You can make your own converter using a single fast cmos gate, resistor, and blocking cap. By using hand-selected gates I was able to achieve less jitter with that circuit than what the Holzworth box was able to achieve.
>
> Doing that conversion can bring down the measured rms jitter on a very good 10MHz sine wave source from 10ps+ to less than 2ps - basically at or below the noise floor of the dts.. Once you run at the units' noise floor, you know your source is quite good..
>
> Bye,
> Said
>
> Sent From iPhone
>
> On Aug 20, 2013, at 18:51, Ed Palmer <ed_palmer at sasktel.net> wrote:
>
>> Adrian,
>>
>> I used Timelab to assess the reaction of the DTS-2077 to different sine wave inputs.  The differences in the noise floor are surprising.  The attached picture was made by taking the output of an HP 8647A Synthesized Generator through a splitter, and then through different lengths of cables to the inputs of the DTS-2077.  The combination of splitter and cable loss meant I couldn't get +7 dbm @ 1 GHz.  If I could have, the 1 GHz line might have been lower than it was.
>>
>> Ed