[time-nuts] HP 105B Problem?

Ed Palmer ed_palmer at sasktel.net
Sat Aug 8 23:13:29 UTC 2009


Thanks for the reply John.

J. Forster wrote:
> Likely yes, but check the spec. If the output circuit is a low Zout buffer
> amp and two separate roughly 50 Ohm resistors, they should be independent.
> Or, two distinct buffers could be used too.
>   
Ah yes, the spec that's in the manual that I don't have!  :-)  I don't 
know if HP often revises specs or procedures on newer versions of the 
same model number.  If not, my unit has a problem.
> You can do a simple check with an Ohmmeter, with the unit powered OFF.
> Measure the R between the front and rear output center pins. If it's close
> to zero, they are likely just paralleled, not individually buffered.
>   
Yes, the front and rear outputs are directly connected - no resistors or 
buffers.
> As to the amplitude growth, try a different cable length., It might be a
> resonance w/ the cable length terminated by the 'scope's C.
>   
I just realized that it's not the device on the end of the cable, it's 
the cable itself.  Attaching a cable with nothing on the end causes the 
meter reading to increase.  Not the kind of thing you expect from HP.  I 
tried the same test on an RF generator at 10 MHz and a similar signal 
level.  The cable length had no effect on the signal amplitude.  
Definitely pointing to a circuit trouble.

Ed
> Best,
> -John
>
> ============
>
> [snip]
>   
>> In summary, should I be able to use both front & rear connectors
>> simultaneously without disrupting the other outputs and does it make
>> sense that high impedance connections cause the 5 MHz level to rise?
>>
>> Sorry for the rather long message.  Thanks for any help anyone can
>> provide.
>>
>> Ed
>>     



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