[time-nuts] PDIP package 100 MHz decade dividers

[Richard (Rick) Karlquist]

On 7/18/2020 6:25 PM, Magnus Danielson wrote:
> Hi,
> 
> A similar approach is used in the 10811 replacement oscillator setup for
> the 5065, where a 7474 is used to divide 10 MHz to 5 MHz. Signal
> conditioning consists of a DC-blocking cap and a pair of resistors to
> bias the mid-point. The produced noise is at least 10 dB worse than you
> would expect. This impacts long term stability response as I have
> reported earlier.
> 
> At least using the square-up design in TADD-2 would help, even thought
> that one won't work for 100 MHz, so it needs a bit of tuning. There are
> chips that solve this.
> 
> Cheers,
> Magnus
> 

Yes, the simple pair of resistors doesn't work well on TTL.
That was probably done by a production engineer, who was
working above his pay grade.  We can't all be Len Cutler.

OTOH, that circuit works well with 74ACXX circuits.  We did that
at 80 MHz in the 5071A and it worked well.

Back in the 70's when I worked for Zeta Labs, my boss taught
me to use a 1 transistor buffer that had a pull up resistor
on the collector and a resistor from the collector to the
base and a resistor from the base to ground.  We used it
in all our designs and it worked well, despite being
ridiculously simple.  My boss was really smart.

That is what they should have used in the 5065.

Rick N6RK