[time-nuts] Trimble Thunderbolt and David Partridge divider board question

Bob Camp kb8tq at n1k.org
Mon Oct 12 18:29:01 EDT 2015


A little quick clarification for those who don’t spend a lot of time studying 
PC board electro-magnetics:

Reference conductor = that thing you labeled ground on the pc board. 

Ground = when you trip while walking the dog, it’s the thing you hit ( = earth)

No that’s not the complete story, but it’s enough to get you going. 


Think of what happens to a box with big leads on either side of it. Consider
equal length cables. Looks a lot like a dipole with a connection in the center
doesn’t it? That’s exactly what happens in some situations. The cables pick
up the RF and max current hits right in the middle …


Hope that helps.


> On Oct 12, 2015, at 4:25 PM, Chris Caudle <chris at chriscaudle.org> wrote:
> On Mon, October 12, 2015 9:08 am, Chris Wilson wrote:
>> I have found when the TX is on at 136kHz the Trimble / divider
>> baord output goes wild and a clean square wave goes seemingly random
>> on my scope with noise.
> How are your input and output cables physically configured?  I noticed on
> the link that Dave just posted that he uses a divider board inside a
> conductive enclosure, and the input connectors are fed from short coax
> cables which have their shields all connected to the same metal panel of
> the enclosure.
> The printed circuit board has input and outputs on opposite ends of the
> board, and the connector shells appear to be connected to the circuit
> reference conductor, which means that if the input and output cable
> shields are not close together and connected together electrically very
> well, all the shield current will be forced to flow across the printed
> circuit board reference conductor.  Perhaps with your transmitter
> operating so closely it is resulting in a lot of ground bounce at the
> various components on the divider board.
> As you say, connecting the 10MHz directly without the divider in place
> would help confirm or eliminate that possibility.
> -- 
> Chris Caudle
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