[time-nuts] My DIY frequency counter and a request for help

[paul swed]

You went quite??

On Sat, Feb 27, 2010 at 9:54 AM, paul swed <paulswedb at gmail.com> wrote:

> Gerard you have some great comments already and welcome back to the
> electronics hobby.
> A couple of things.
> Curious about whats on the board etc.
>
> Here would be my thoughts.
> If the same 10 MC signal thats the reference is also the input.
> Then any funny numbers are the process leftovers or jitter.
> I think this would also help you find the max resolution quickly.
> Once you introduce external signals it becomes more difficult to understand
> whats happening.
>
> I built a LORAN C simulator driven by a Rb reference.
> When I drive the austron 2100 with the same reference the austron
> ultimately settles at its max resolution of 1 E-13.
> Very interesting first project you clearly have a good background in
> applied electronics
>
>
> On Sat, Feb 27, 2010 at 7:36 AM, Bruce Griffiths <
> bruce.griffiths at xtra.co.nz> wrote:
>
>> Gerard PG5G wrote:
>>
>>>    Hello all,
>>>    First post here, so I'll start with a quick introduction. I trained as
>>>    an electronic engineer but don't work in that field any more, which
>>> has
>>>    given me the appetite back to do some electronic engineering as a
>>>    hobby. I have been a licensed ham for over 25 years (more than 60% of
>>>    my life I realised the other day) and used to be rather active on HF
>>> as
>>>    PA3DQW. At the moment I live in the UK where I am licensed as M0AIU.
>>>    I recently designed and build a frequency counter and I need some help
>>>    with verifying its performance. I believe it gives me 11 digits in 1
>>>    second. I say believe because I have not got the hardware to verify
>>>    this. At the moment my assumption is based on calculations and limited
>>>    testing with the equipment available to me.
>>>    My counter is a "continuous time stamping reciprocal counter". I
>>>    implemented this as a USB powered device, with the hardware taking the
>>>    time stamps and sending it over USB to a windows PC. Some software
>>>    written in C++ takes care of analysing the data.
>>>    The hardware takes 5000 time stamps per second using a high speed TDC.
>>>    The hardware is a single PCB measuring about 50 by 80 mm. it requires
>>>    an external 10MHz reference and apart from using this as the time base
>>>    it also uses this for self-calibration of the TDC. The unit requires
>>> no
>>>    further calibration.
>>>    The PC software takes these time stamps and the associated counts and
>>>    uses regression to calculate the slope. This slope represents the
>>>    frequency of the input signal. I am sure people on here are familiar
>>>    with the counters made by Pendulum, and I have to confess that their
>>>    marketing material was helpful in putting this thing together.
>>>    Since the hardware is true zero dead time, the final capabilities of
>>>    this counter are determined by software. At the moment I can
>>>    simultaneously display the input at multiple gate times (see the
>>>    attached screen shot). For gate times over 1 second I have the option
>>>    to use overlapping gates, so that the display gets updated every
>>>    second.
>>>    Because there is no dead time I can also calculate Allan Deviation.
>>> The
>>>    two displays at the bottom of the page show both normal and
>>> overlapping
>>>    Allan deviation at tau=10s. I am still working on the software to do
>>>    this at multiple tau in real time and display it as a graph and a
>>>    table.
>>>    So, after this lengthy introduction here is my request for some
>>>    assistance. Is there somebody on the list who can assist me in
>>>    verifying the performance of this frequency counter? Ideally somebody
>>>    with access to two highly stable and known frequency sources. I can
>>>    send the hardware by mail, but if there happens to be somebody with
>>>    this kind of gear not too far from where I am (50 north of London) I
>>>    will travel. In exchange you get to keep the hardware and will be
>>>    supplied with whatever software I come up with.
>>>    Thanks in advance and regards,
>>>    Gerard, PG5G
>>>
>>>
>> Are you calculating ADEV and MDEV using the slopes determined by the
>> regression fit?
>> If so, what you calculate isn't ADEV or MDEV.
>>
>> You need to use the raw timestamps taken at a rate of 5000/sec directly to
>> produce estimates of ADEV, MDEV.
>> What is the resolution of the TDC?
>>
>> Bruce
>>
>>
>>
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>
>