[time-nuts] EIP545A 18GHz counter query

[Charles P. Steinmetz]

Chris wrote:

>I have the 10MHz output from David's divider feeding the counter. When
>fed from this the Band 2 seems unreliable starting at 10MHz. If I feed
>it 10Mhz at 50mV from my sig gen it starts reliably. Is it a mismatch
>from the divider, or has it perhaps not got enough drive level?

First, what does the counter manufacturer's specification say with 
respect to acceptable signals at the external reference input?

Second, what happens if you feed the TB output directly to the 
counter's reference input?

IIRC, the outputs of the Partridge divider are 5V TTL from a ~50 ohm 
source, so low peak-to-peak signal amplitude should not be an 
issue.  If anything, the divider could be overdriving the counter's 
reference input.  Note that the TTL signal ranges from 0V to ~+5V and 
does not cross ground -- if the counter is expecting the reference to 
be bipolar (i.e., if it switches on a zero-cross), it may not respond 
reliably to TTL levels.

Beyond that, depending on how the counter terminates the external 
reference line, you may have steps or ringing at the reference input 
(see the thread on terminations).  Look at the counter's reference 
input with a high-impedance (divide by 10) scope probe to see what 
the feed looks like there.

Best regards,

Charles