KIT FAULTS
& MODIFICATIONS
1/ This applies to Kits supplied
prior to April 2009. I have received information
from one constructor that he was unable to make his transmitter
stable & it would not produce a correct picture on a TV monitor.
He had tried tuning it for many hours & I expect that many others
have had the same problem. The Toko coil supplied, coil L1 should
be a 0.13uH not 0.1uH & should be marked 100 114 on the can.
The 0.13uH coil along with the parallel 33pF capacitor is resonant
close to the 71 to 74MHz crystal frequency. The incorrect 0.1uH
coil makes it resonant somewhat higher in frequency, so it cannot
be tuned down to the 70MHz region. See the notes eme65doc
by Kevin ZL1UCG Kit on how to determine what frequency the coil/capacitor
combination is resonant. The coil may be able to be modified by
removing the can & adding an extra turn to the coil, but this
could be difficult for some constructors. Please
email us if you have the problem & we will post a replacement
coil to you.
2/ Many
problems associated with this Kit are due to poor soldering or the
chip capacitors not being soldered or they may have been cracked
when fitted. Problems also exist with the two coils L2 & L3
not being wound correctly with the correct number of turns &
spaced above the board by 2.5mm. The coils are rather critical,
& if they have a turn less or more, then the two trimmer capacitors
C1 & C2 associated with the tuning of the coils will not peak
at the 3rd harmonic, ( 213/222MHz ) of the crystal. Refer to the
Images above on how the coils should look.
3/
There have been reports of spurious signals from the output depending
on the tuning of the L1 & the trimmer capacitors. First check
to make sure that the crystals case is grounded to the board by
soldering some wire from the crystal case to the top of the board.
I have also come across
a crook crystal that when L1 was adjusted, the adjustment was very
critical to make the crystal lock on frequency. L1 was very rubbery
& the frequency could be tuned many MHz either side of the crystals
frequency. The other symptom of the crook crystal
was nearly a 5dBm loss of output power from the transmitter. If
the crystal is good then L1 should be able to be tuned in either
direction & only the output power will drop, but the frequency
will remain locked to the crystals frequency. Also check that the
1nF chip capacitor on the first BFR92A is soldered & not cracked.
If you have not checked if you have the correct Toko coil fitted
then refer to section 1 above first.
4/ Any problems with burning
up of either of the 10ohm resistors could be due to a shorted trimmer
capacitor C3 or C5 on the associated tuned circuit. Check the trimmer
with a multimeter for intermittent shorts by adjusting it.
4/
If you have low output power & trimmer capacitor C3 or C5 won't
tune, then a common problem is one of the two 220pF chip capacitors
that are soldered on the bottom of the board, many not be soldered
on one end, or one is cracked.
5/
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 circuit correctly.
6/ Changes
to Kits after April 2009 These changes are
to make the Butler Oscillator very stable & make tune up very
easy. Previous versions of the kits were difficult to tune due to
the high gain in the oscillator circuit which caused spurious output
with some settings of L1 & C1 & C2 trimmer capacitors. The
27pF is changed to a 10pF, The 78L08 regulator is changed to a 78L05.
No other changes are needed. Initial settings for L1 is with the
core even with the top of the coils can, C1 80% mesh, & C2 70%
mesh.
Saturday
18th April 09 
