CCWN 75:33
                                                  
        Normal operation of the PM-1 remains possible, except
that the 80/40 meter VFO switch is no longer accessible from the
front panel.          The center contact on the panel of the
panel mounted OFFSET switch provides a convenient metering point,
using a VTVM to observe the phase lock of the VWFO onto the
signals coming from the frequency standard into the frequency
stabilizer. This eliminates the need for a separate monitoring
receiver to detect the phase locked synchronization of the
oscillators, once operator experience is gained.         
Isolation Amplifier : Initial tests indicated that the
suppression o- TTL interference generated by the logic circuits
would be one of the greatest challenges faced by amateur CCW
operators. Exhaustive shielding, bypassing, use of RF chokes in
DC control lines and other measures narrowed the coupling medium
of undesired interference down to the RF sampling line from the
TEN-TEC to the frequency stabilizer. A simple cascade isolation
amplifier, constructed in a separate case with ample shielding
and bypassing corrected this final leak into the receiver. The
unit is shown in photo 6 and schematic 4. The +12 volt power for
the unit is drawn from the same batteries used to sower the
TEN-TEC.   The CCW Filter: The Coherent CW filter described here
is an improvement on the original CCW filter designed by W7GHM.
The filter is shown in schematics 5 and 6 and in photographs 7
and 8. Its input, the desired CCW signal at precisely 1 Khz plus
any additional noise or QRM should be at about 300 millivolts.
The filter has about 40db gain at the desired frequency. The only
other input required is a 4 Khz TTL signal from the auxiliary
divider board in the frequency standard. This provides the
driving pulses to activate switches U2, U3, U5, which operate the
synchronous balanced mixers, integrator, sampling, and balanced
mixer sections. U9 varies these driving pulses in steps of l/lOth
of the dit period through switch S-1, permitting time
synchronization of the CCW filter to the exact time pattern tat
the CCW keyer at the distant station has generated.      System
Interconnection and Component Selection: The inter     
connection of the various elements of the station is straight
forward and is shown in schematic 7. Construction of a final unit
could consolidate some of the components. However, in the
development of this prototype model, the units were built
separately and interconnected using shielded grid wire.
Construction techniques are generally non-critical, except for
the isolation amplifier, which should be built as shown.         
Surplus IC devices and transistors should be carefully tested,
especially those used where RF signals are switched. Some IC's
will give poor service, and can best be located through the use
of an oscilloscope. The most important factor is the presence of
good ,clean square-wave waveforms. Generally, difficulties were
experienced with IC's that would not switch to the low state
cleanly, or that would gradually rise to the Vcc level. Unless
first run premium IC's are used, sockets are almost a necessity.