[time-nuts] EIP545A 18GHz counter query

Chris Wilson chris at chriswilson.tv
Thu Nov 29 18:00:52 UTC 2012



> 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



29/11/2012 17:32


It's definitely playing up, and I don't think I have it right with
regard to it being because I am feeding it from David's divider. I let
it go cold this afternoon and have just come to it now. Even with the
signal into  Band 2 direct from my sig gen at 1 volt it doesn't start
counting unless I go to, or over, 185 MHz. Band 3 is fine from cold,
as is Band 1. I'll get some freeze spray and see if I can isolate any
part. I'll also have a go with the air line. So near to being fine,
must be something pretty minor?

Band 2 should work from -20dbm (22mV RMS) right across its 10 MHz to 1
GHz range according to the manual. Even with 190 MHz into it it takes
at least 30mV to start triggering, sometimes up to 40 mV.  40 mV will
reliably fire it across its full range once it warms up a bit.

Band 1 specs are 22 mV from 10Hz to 1 GHz, and that band triggers with
just 15 mV at 10 MHz, but needs 25 mV at 100 MHz.

Band 3 specs are  12 mV at 1 GHz to 1.2 GHz (needs 15 mV @ 1GHz)

1.2 to 12.4 GHz should trigger at 7 mV but my sig gen stops at 1040
MHz so can't test.

Thanks for your input Charles.



-- 
       Best Regards,
                   Chris Wilson.




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