FAULTS & MODIFICATIONS
1/ New changes to Kits after
September 17th 2009. These changes are to reduce spurious output
by adding extra bypass capacitors & a schottky diode pack
across the Toko coil. Solder a 1nF chip
capacitor on the junction of the 560ohm resistor & L1 coil.
The chip capacitor should be soldered between the 560ohm resistors
lead & the groundplane on the top of the board. Solder a
BAS70-04 schottky diode pack across the coil L1 on the bottom
track side of the board. Solder a 22pF ceramic leaded capacitor
from the 1kohm resistor that is connected to the emitter of
the first BFR92A to ground. The capacitor is fitted on the bottom
track side of the board & the leads are cut short. If you
are still having trouble with spurious output when tuning then
try changing the 78L08 to a 78L05 regulator that will reduce
the gain of the oscillator stage with minimal affect on output
2/ There are a number of
modifications below suggested by Kevin ZL1UCG that may improve
the oscillators performance. You should only attempt these if
you know what you are doing, & are only suggestions. A few
changes can be made to the powersupply to improve frequency
stability & quality, ( reduce phase noise ), the 78L08 regulator
was removed & replaced with a 15ohm resistor. A separate
7808T regulator is now used off the board to feed the complete
oscillator. 10uF capacitors are fitted on each side of the regulator.
Even better results can be obtained by using a very low noise
regulator, as standard regulators are very noisy. Phase noise
may also be reduced by fitting a 47uF capacitor from the base
connection of the first BFR92A to ground, & replacing the
1kohm resistor between the bases of the two BFR92A transistors
with a 1uH inductor. Also fitting a 1uH inductor in series with
the 1kohm emitter resistor as shown may improve phase noise.
3/ The 27pF capacitor on
the collector of the first BFR92A was replaced with a 10pF which
significantly reduces the frequency change with power supply
voltage. Applying notes 1 & 3 above significantly reduces
the crystal dissipation. Excess crystal dissipation an affect
drift aging & failure of the crystal.
4/ The 2nd multiplier also
appears to be over dissipating & the 10ohm resistor can
be replaced with a 100ohm & the interstage capacitor 15pF
can be changed to 6.8pF. The output power is still around +10dbm
output run off a 8 volt supply.
5/ A number of constructors
have reported the 10ohm resistor burning up when tuning the
4th trimmer capacitor. The problem seems to be that some of
the trimmers may be faulty & short out at some point where
the trimmer is set. Check the trimmer with a multimeter if you
have found this problem & replace if needed.
6/ If you have low output
power & trimmer capacitor TC3 won't tune, then a common
problem is one of the two chip capacitors that are soldered
on the bottom of the board, many not be soldered on one end,
or one is cracked.
Many tune up problems can be traced to the two coils being wound
incorrectly. Please refer to the pictures on the above
on how they should look.
8/ The crystal frequency
can be moved down approx 2kHz using a 100nH inductor in series
with the crystal & around 15pF capacitance is seires is
needed to move it up by the same amount. A small NPO trimmer
capacitor can be tried in series with the crystal for fine tuning.
Only use what is required to bring the crystal onto frequency.
If the frequency of the crystal is way out, then the crystal
should be replaced. The Toko coil should not be used to try
& move the crystal frequency by more that a few hundred
Hz else the oscillator becomes unstable.
9/ Tests by Kevin ZL1UCG
on the Capacitor & Coil combination used in the Butler Oscillator.
eme65doc The chart has recommendations
for the capacitor that should be used to resonate the tuned