Wasn't that a RTL 923 and 914? I still have a few from my learning days.
John WA4WDL
--------------------------------------------------
From: "Brooke Clarke" <[email protected]>
Sent: Thursday, April 15, 2010 11:24 AM
To: "Discussion of precise time and frequency measurement"
<[email protected]>
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<[email protected]>
Date: Thu, 15 Apr 2010 13:42:00
To:<[email protected]>
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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