CCWN 76:78
A CCW FREQUENCY STANDARD by Ray Petit

              Page 76:77 gives a diagram for a frequency standard
for CCW. The circuit is a modernization and
adaptation of Irv Hoffs "Mainline FS-1" frequency standard. It
accepts power supply voltages from 9 to
15 volts but does not contaminate the power supply lines with
r.f. from the oscillator and drivers. The
circuit delivers two independent I MHZ outputs having 90 degree
phase relationship. The outputs drive
50-ohm cables without producing ringing, and the output at the
far end of the cable is directly TTL-
compatible. The two outputs are isolated. Any reverse "kickback"
from external circuits is suppressed
by the driver stages and prevented from contaminating the other
output.

              If the cable is terminated at the far end with a 50
ohm load, the output will be legal TTL levels:
zero and approximately 2.5 volts. If the cable is left
open-circuited (greater than 500 ohms impedance)
the output, as seen at the open-circuited end, will be zero and 5
volt levels, also TTL-compatible.

             C2 and C3 are temperature-compensating types
selected for the particular crystal. The oscillator
design makes the output frequency particularly insensitive to
variations in the transistor characteristics.
Q2 and Q3 are a differential limiter with TTL output to IC1. IC1
divides by four, giving the two-phase
output. Q4-Q7 produce outputs of (for practical purposes) zero
impedance. The 51 ohm resistors R13
and R14 match the cable and absorb reflections. IC2-lC4 are 5
volt regulators. The heavy bypass capacitors and the pass
transistors Q8-Q10 prevent the switching transients in the
circuit from contaminating
the power supply and radiating via the power supply wires.

             If there is interest we could arrange for this unit
to be supplied in ready-to-operate form in a Po-
mona box for about S100. Please drop me a note if you are
interested.

COMMENTS

             Ray Petit reminded me that the system used by DJOLN
will fade in and out during operation as the
local oscillator drifts slowly with respect to the incoming
signal. In the Petit filter this is avoided by us

             ing 2 channels with a 90 degree phase relationship
and combining them. Woody