[time-nuts] Trimble Thunderbolt 1pps

[Said Jackson]

Hal,

Your plots don't show the wave being reflected by the cable end, and bouncing back and forth.. Until settling down.

Without an end-termination the improperly terminated output of the Thunderbolt will cause the signal to bounce back and forth..

If there is a 50 ohms termination, there won't be any bounces, but a large voltage drop will happen due to the relatively high DC current over the long cable resistance.. (5V into 50 Ohms = 100mA).

Maybe thats why the levels at the end are so much lower that at the source?

Bye,
Said

Sent From iPhone

On Jan 3, 2014, at 15:26, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> albertson.chris at gmail.com said:
>> The "line driver" was a TTL inverter chip  I was going through about 50 or
>> 60 feet of cat-5 wire. TTL level serial is always marginal, the specs say it
>> should not work but it does work most of the time.
> 
> Modern CMOS chips work much better than real TTL.  Some CMOS chips have weak 
> drivers.
> 
> Cat-5 should be fine for 100 ft.
> 
> Here are scope pictures from the PPS signal from a TBolt driving 100 feet of 
> various types of wire:
>  http://www.megapathdsl.net/~hmurray/time-nuts/coax/Coax-20ns.png
>  http://www.megapathdsl.net/~hmurray/time-nuts/coax/TP-20ns.png
> The clump on the left of each graph is the input.  The stuff on the right is 
> the output.  The scatter is due to the different prop times.
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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