[time-nuts] lunatic fringe time standards

Bob Camp lists at rtty.us
Thu Apr 15 12:05:37 EDT 2010


Hi

The only real limit on a Johnson counter is how clever you get making sure
that only one stage is a 1 and all the rest are zeros. There are *lots* of
ways to take care of that, each with it's own set of trade offs. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Brooke Clarke
Sent: Thursday, April 15, 2010 12:00 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] lunatic fringe time standards

Hi John:

Yes RTL and 3.3 V if I remember correctly.

Have Fun,

Brooke Clarke
http://www.PRC68.com


jmfranke wrote:
> Wasn't that a RTL 923 and 914?  I still have a few from my learning days.
>
> John  WA4WDL
>
> --------------------------------------------------
> From: "Brooke Clarke" <brooke at pacific.net>
> Sent: Thursday, April 15, 2010 11:24 AM
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] lunatic fringe time standards
>
>> Hi Didier:
>>
>> When working with high speed data, for example an IDE hard drive, 
>> where there are parallel data lines you get into the same problem as 
>> you have with a shaft encoder where there are parallel binary data 
>> lines.  In the case of the shaft encoder mechanical misalignment can 
>> cause huge errors at the transitions and in the hard drive jitter and 
>> time delays can cause similar problems.  I think that was one of the 
>> main motivations to go to a serial hard drive interface (SATA).
>>
>> When in college I used a Johnson counter made from the first ICs from 
>> Fairchild, i.e. the 723 flip-flop and the 714 two input gate.  The 
>> beauty of the Johnson counter is that you can decode it's state with 
>> ten each two input gates.
>> http://www.prc68.com/I/comp.shtml#Nixie
>>
>> Have Fun,
>>
>> Brooke Clarke
>> http://www.PRC68.com
>>
>>
>> Didier Juges wrote:
>>> I believe Gray code was invented to support absolute mechanical 
>>> position encoders, where the speed of the electronics is high 
>>> compared to the speed of the hardware being monitored. It eliminates 
>>> the potentially large error between two positions since only one bit 
>>> changes at a time. This is done at the expense of complicated logic, 
>>> which goes against speed.
>>>
>>> I don't think Gray code has ever been used to implement fast 
>>> electronic counters. That's what synchronous counters are for, and 
>>> when synchronous counters are not fast enough, use a prescaler. It 
>>> will just take more time to get the precision you need.
>>>
>>> Unless you need fractional Hz resolution at THz speed, a prescaler 
>>> is the way to go.
>>>
>>> Didier
>>>
>>> ------------------------ Sent from my BlackBerry Wireless thingy 
>>> while I do other things...
>>>
>>> -----Original Message-----
>>> From: Eugen Leitl<eugen at leitl.org>
>>> Date: Thu, 15 Apr 2010 13:42:00
>>> To:<time-nuts at febo.com>
>>> Subject: Re: [time-nuts] lunatic fringe time standards
>>>
>>> On Thu, Apr 15, 2010 at 07:30:27AM -0400, Bob Camp wrote:
>>>
>>>> Hi
>>>>
>>>> I'm not 100% sure I understand exactly what you are thinking about 
>>>> setting up.
>>>>
>>> This is completely theoretical at this point. Just the required 
>>> geometry
>>> size would be prohibitive.
>>>
>>>
>>>> My guess is that the counter needs to run at the same THz speed as
>>>> the oscillator. That's pretty fast. I suspect that what ever you use,
>>>> speed / propagation delay in the counter it's self will be an issue.
>>>> That will get you back to either a ripple counter or a Johnson 
>>>> counter.
>>>>
>>> Wouldn't you get large errors when you caught a ripple
>>> during readout? That wouldn't be a problem with a Gray code.
>>>
>>>
>>
>>
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