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
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