[time-nuts] HP 5316B External Reference

[Wes]

Thanks for your insights Rick.

The manual specifically states:  "The HP 5316B does not actually use the 
external input signal for a time base but locks-on to the signal with an 
injection-lock-multiplier. The external signal must be 1,5, or 10 MHz...."

My only experience with injection locking was with the Phoenix Missile IMPATT 
diode "amplifier" which was actually three circulator-coupled oscillator stages 
using one, three and sixteen diodes respectively.

I don't currently own one of these counters, I'm just investigating the idea of 
using one for off-the-air frequency measurements where the unknown is mixed down 
to audio.

Wes  N7WS

On 7/11/2020 6:46 PM, Richard (Rick) Karlquist wrote:
>
> On 7/11/2020 3:51 PM, Wes wrote:
>> As I understand it this counter has an external reference input that isn't 
>> used directly as the time base but injection locks the internal time base.  
>> Does anyone here know how well this works. Is using a GPSDO as a reference a 
>> worthwhile accuracy improvement?
>>
>> Wes Stewart  N7WS
>>
>
> I worked in Frequency Counter R&D at the HP Santa Clara division
> around the time the 5316B introduced, but didn't know about
> this detail.  AFAIK, most counters we made did NOT work this way.
> Whatever external reference you fed in (warts and all) was used
> to clock the counter.
>
> OTOH, most RF instruments (other than counters) used a PLL
> (not injection locking) to lock the internal oscillator to the
> external reference.  IMHO, this architecture only made sense
> on sig gens and spec ans, not on counters.
>
> I will point out that the 5316B was a cost reduced version of the
> 5316A.  I was the project manager for the 5334B, which was a
> cost reduced version of the 5334A.  I believe there was a third
> model where the B version was cost reduced from the A version,
> but I don't remember which one.  As a group, these were called
> the "killer B's" because they would supposedly kill off Racal
> Dana sales or some silly marketing nonsense to that effect.
>
> It's possible that for some obscure reason, a scheme was employed to save 
> money that superficially resembled injection locking.
> I'm guessing a multifunction chip was used that had a
> built in oscillator with an external crystal, but no access to the connection 
> from the oscillator output (on the chip) to the downstream circuit.  Are you 
> sure that the 5316B actually uses injection locking, rather than having the 
> external reference simply drive the crystal pins
> on the IC?  This would be easy to verify by feeding
> in an external reference that was say 100 ppm off frequency
> and seeing if the counter still worked OK.  No injection
> locking scheme AFAIK would ever pull that far.  If it actually
> is true injection locking, the problem is that whether it worked
> would depend on the relationship between the free running
> frequency and the external reference frequency, of course.
> IOW, it might work in some cases and not in others.
>
> Rick N6RK
>