[time-nuts] Why using HP5370 ext-ref is (maybe) a bad idea

[Magnus Danielson]

On 03/03/14 23:59, Poul-Henning Kamp wrote:
> In message <531505BC.4050900 at rubidium.dyndns.org>, Magnus Danielson writes:
>> On 03/03/14 22:35, Poul-Henning Kamp wrote:
>>> In message <5314EF87.1020204 at rubidium.dyndns.org>, Magnus Danielson writes:
>
>> Indeed. Let's assume that it's not the BBB causing the issue, but it's
>> inherent to the 5370 design.
>
> Charles reminded me of this document in private email:
>
> 	http://www.ko4bb.com/Manuals/06)_App_Notes_-_Proceedings/HP_5370/HP5370-DNL-Mod.pdf
>
> It explicitly mentions the 5370A, so I guess a check is in order
> if the ...B has these changes already.

That's the one I mentioned earlier. I also recall it was fixed in the B.

>>>> Those with a high quality RF generator could force-feed a 200 MHz into
>>>> the counter and see if it makes any major difference.
>>>
>>> Yes, that would be an interesting experiment.
>>
>> It's a bit problematic thought, the signal is fed to three different
>> places, A19, A20 (the interpolators) and A22.
>
> I would go for TP1 at A21 ?

Well, either you lift R1 and insert the signal into that one, or you 
lift C15 and insert signal there... and use that amplifier chain.

Just inserting on TP1 isn't very smart, even if you unplug the 10 MHz 
input to the multiplier chain.

Think I will sniff with the near-field probe tomorrow.

Cheers,
Magnus