frequency counter mod

[VK4ADC]

A 74HC4017 will go up to about 50MHz, divides by 10, 1:1 high to low duty cycle. Put a schmitt trigger squarer in front (assuming the GPSDO outputs 10MHz sine wave) and put that into your dist amp - or alternatively steal the LM7171 output section of https://www.vk4adc.com/web/general-proje.../72-lctcxo in lieu.


https://www.ti.com/lit/ds/symlink/cd74hc4017.pdf
10MHz fed to CLOCK, pin 14
1MHz out from Terminal Count, pin 12.
ground on pins 8, 13, 15.
Supply to pin 16. 

Schmitt squarer : HC14, hex inverter
http://www.ti.com/lit/ds/symlink/sn74hc14.pdf

                    ----- 1Mohm---- 
                   |                      |
INPUT o-- C ------- INV -------------- INV ------- HC4017 ----- C ----o  O/p at /10 (SQ wave)
                                                              Clk          TC |
                                                                                 |------- INV ---- C ----o      Option: 4 sq wave isolated outputs @ 1MHz
                                                                                 |--------INV ---- C ----o
                                                                                 |------- INV ---- C ----o
                                                                                 |------- INV ---- C ----o

10MHz input level is assumed to be at least 1V Pk-Pk.
C is DC block, 103n  to 104n, actual value not critical
1Mohm makes the single schmitt inverter act slightly more linearly ie. accepts signals more sinusoidal in form
Make sure you add 104n caps to "ground" as RF bypasses directly on the VCC supply pins of the two ICs, pin 14 of HC14, pin 16 of HC4017.

Optionally add another HC14 INV section after the HC4017 TC output to give isolation protection.  Alternatively tie all 4 spare INV inputs to the TC pin and that gives you 4 separate sq wave outputs at 1MHz.....

Supply voltage is not critical but >= 5VDC for fast switching speeds.