[time-nuts] Wavecrest DTS-2077 Teardown

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Aug 21 01:28:22 EDT 2013

The same analysis applies however one would probably use something like 
cascaded longtailed pairs with well defined gain (series emitter 
feedback) and the low pass filter cap connected between the collectors 
rather than opamps.


Ed Palmer wrote:
> Does anyone know if this situation would benefit from doing something 
> similar to a 'Collins Hard Limiter' i.e. instead of squaring the 
> signal in one stage, use maybe two or three cascaded stages with 
> increasing bandwidths? Normally, Collins limiters are used with beat 
> frequencies of less than 1 KHz, but maybe there's value in doing at 
> typical time-nuts frequencies.
> Any thoughts?
> Ed
> On 8/20/2013 10:02 PM, Said Jackson wrote:
>> Hi Ed,
>> For anything up to about 150MHz try the NC74SZ04 types from National 
>> if you can find them NOS. they stopped making these years ago.. 
>> Fairchild is ok too but not as fast from what I have seen.
>> Forgot I wrote about it in 2009. Oh boy -age kicking in.
>> Bye,
>> Said
>> Sent From iPhone
>> On Aug 20, 2013, at 20:17, Ed Palmer <ed_palmer at sasktel.net> wrote:
>>> 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
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