[ntp:questions] NTP sever on an isolated Network

Speechless noone at nowhere.com
Mon Jan 19 12:18:38 UTC 2009


On Mon, 19 Jan 2009 02:25:33 -0700, Brian Inglis wrote:

> On Fri, 16 Jan 2009 00:50:02 GMT in comp.protocols.time.ntp, Unruh
> <unruh-spam at physics.ubc.ca> wrote:
> 
>>"David J Taylor"
>><david-taylor at blueyonder.neither-this-bit.nor-this.co.uk> writes:
>>
>>>Unruh wrote:
>>>[]
>>>> Yes, but that same manual says that the voltage for the 18PC version
>>>> is 8-30V. It says nothing about the internal voltage being the 4.5 to
>>>> 5.5 V.
> 
> Not quite - the tech spec states that the unit accepts 8-30V only using
> the supplied cigarette lighter adapter. RTFM
> 
>>>> And the 18PC and the 18LVC are different units with different inputs
>>>> and outputs.
>>>> The PC is also the one with serial port output and the serial port
>>>> standard says that the voltage is -12 to 12V on the serial pins.
> 
> The standard says min +-5V transmitted and +-3V received.
> 
>>>> Now, many
>>>> serial cards
>>>> do accept 0-5V (TTL) which is why the 18LVC works on many serial
>>>> ports without a voltage converter,  but that is out of standard.
> 
> They are well outside the V.24 actually V.28/RS232C standard as those
> require 3V min magnitude.
> 
>>>> Does the
>>>> 18PC follow the standard? The manual does not say.
> 
> The manual does say these units conform to TIA232F standard.
> 
>>>> Ie, there is
>>>> NOTHING in the manual which
> 
> Non sequitor.
> 
>>>> would allow one to conclude that the actual voltage delivered to the
>>>> unit
>>>> is 5V rather than the 8-30 V that the manual does say that the unit
>>>> requires. You might be right that a) it is the lighter adapter than
> 
> The manual clearly states the cigarette lighter adapter accepts 8-30V.
> 
>>>> lowers
>>>> the voltage to 5V, and b) that the output does not follow the serial
>>>> port
>>>> standard of -12 to 12V, but I would like something other than your
>>>> speculations to go by.
> 
> Common sense and Occam's razor say the base units accept the same
> voltage as the rest of the line.
> Not something to accept without measuring the adapter output if you're
> hacking hardware.
> 
> No 232 standard requires +-12V.
> 232C allows 25V output and 15V input open circuit, +-5-15V into 3K-7K
> ohm loads.
> 232F allows TTL levels for cheaper local circuits.
> 
>>>Section 1.4.2 of the manual says that the RS-232 levels sent are 0..+5V
>>>for the PC version, and from 0..Vcc for the LVC version, where Vcc is
>>>the supply voltage.
>>
>>You are right. I had not seen that. Those are of course NOT rs232
>>specified levels, but many serial cards to support them
>>
>>>I would be surprised if the internal electronics differed significantly
>>>between the PC and the LVC.
>>
>>I would not be surprized either way. The units differ. One puts out PPS,
>>th e other does not. The USB puts out USB signal trains. The LVC and PC
>>put out NMEA etc. However again, it would be interesting to discover if
>>the volatage sent to the unit in the PC configuration is 5V or 8-30V.
>>They could easily put the voltage reducer into the unit rather than the
>>cigarette plug. or they could put it into the cigarette plug. We are
>>both discussing in ignorance here.
> 
> Easy to discover, spend (discount) CAD80 and measure.

...or read the "NOTICE" on this page:

http://tapr.org/gps_gps18pc.html

Quote:
"Do NOT remove the cigarette lighter male plug on this unit in order to 
use a different connector. The voltage regulater is built into the 
cigarette lighter male plug. If you'd like a wire leads only (5 VDC 
power required) unit contact the TAPR Office."


> 
> Just trying to provide a warning to potential buyers not to expect
> anything much different from the PC unit itself, other than no PPS. ;^>




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