[time-nuts] Ublox 8T - breakout board

[Bob kb8tq]

Hi

The issue with coax becomes:

Do you want to drive a terminated line?

On a board built for a single application, you likely know the answer to that and can 
design appropriately. On a general purpose board, you probably need to allow for
the “worst case” configuration ( = terminated). No, that’s not a recommendation that
one operate that way, only a recognition that a lot of people *do* operate that way. 

Bob

> On Dec 12, 2020, at 11:59 AM, Matthias Welwarsky <time-nuts at welwarsky.de> wrote:
> 
> On Samstag, 12. Dezember 2020 14:40:11 CET Bob kb8tq wrote:
>> Hi
>> 
>> If you are going to drive much with the timepulse output, you will need to
>> buffer it. This is true for just about any practical length of coax. It also
>> applies to other cables once they get past the “few inches” range.
>> 
>> Ideally the coax buffer would be something like 4 or so ‘125 buffers in
>> parallel, each with a 200 ohm resistor in series with their output. Is it
>> going to put out 3.3V or 5V logic? ….
> 
> A HCT125 should have 3.3V logic compatible inputs and TTL outputs. There are 
> nice dual-instance buffers available, 74AHCT2G125 for example. But this is not 
> "breakout board" material any more.
> 
> 
>