The phase lock loop compares the approximately
14,051,000 Hz signal derived from the receiver oscillators with
the 14,051,000 Hz from the station standard. The phase lock loop
locks the derived frequency onto the standard by changing the
frequency of the VFO so that the result (HFO-VFO-BFO) is equal to
that of the standard.            Diagram 1 gives the diagram of
the phase lock loop. I use two general ways of obtaining the
reference frequency upon which to lock. The first, using a
harmonic of a frequency from the station standard (a K4EEU
standard) to input A. For this method, no input is placed at B. 
          For example, with 100,000 Hz from the standard fed to
input A, the oscillator-derived frequency will lock on multiples
of 100,000. This gives reception 1000 Hz below (with LSB) and
1000 Hz above (with U8B) each multiple of 100,000. This method
works down to about 5000 Hz intervals with as low as 5000 Hz
input to A.            For the lower frequencies, I found the 20
meter harmonics insufficient, and use the harmonic booster shown
in Diagram 1. With the harmonic booster and 1000 Hz square wave
to A, lock can be obtained every 1000 Hz. Note, however, a 1000
Hz source presents problems for reception as there is a harmonic
on the desired CCW signal frequency and very careful shielding is
required. Generally it is better to avoid a source which has a
harmonic on the desired frequency.            For the second
method, input A is used in the same way and input B is used for a
low frequency offset. For example, with 50,000 Hz input to A, and
the receiver oscillators set to combine to produce a frequency of
about 14,048,000 Hz, a 2000 Hz signal to B causes the receiver to
lock the oscillators to 14,048,000 Hz. This would provide
reception at 14,047,000 Hz using LSB or 14,049,000 using USB.     
      In operation, a VTVM may be used at point C or D to observe
lock. As the VFO is tuned near to the point where the derived
~frequency matches the (or a harmonic of) frequency from the
standard, the voltage changes suddenly to indicate lock. As
tuning continues, it passes through the ambient value end to 'he
other extreme, until finally it drops back to the ambient value
as lock is lost. The lock is about 400 Hz wide on 20 meters. I
set the tuning in the mid range for operation on the expectation
that this gives the phase lock loop a better chance to control
for any changes in the derived frequency which may occur.         
  Very careful shielding is needed for the phase lock loop. i use
a Pamona box which is quite convenient as it can be opened easily
but also provides good shielding. All leads are shielded.         
  The technique described above can be applied to any receiver.
The frequency control diode would need to be added to most
receivers. A synthesizer could also be used to obtain the
reference frequency.