17-10-2016, 02:43 PM
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'l'he unit described in the article ,,Low Cost Wobbulator",
which appeared in last month's issue, can be
used on its own with an oscilloscope having a suitable
timebase output, the latter beine coupled to the
variable capacitance diodes in the* wobSuiator. The
combination of wobbulator and oscilloscope then
allows the response curve of an a.m. receiver tb be dis- pl1ye$ on the cathode ray tube of the oscilloscope.
..It is also possible to
'use
the unit with an' oscllloscope,
not ha-ving a timebase output, and this is
acnlevecl by.employrng. a separate timebase generator
tbr the wobbulator. The oscilloscope time6ase then
sryggps the spot across the face ofthe cathode rav tube
while the additional [imebase sweeps the wobbulator
frequency across the receiver passband.
The timebase for the wobbilator aiso produces a
positive. pulse at the srart of the flyback beriod and
the .pulse can be employed to synchionise the
trmebase ot the oscilloscope when this has a triggered
sweep mode. Using the tiigger pulse to synchi-onise
tne two trmebases is not essential, but it does ensure a
stable trace. The author has obtained excellent results
with.this.synchronising.technique using a Russian Cl-
16 double beam oscilloscope, which" is compietely
devoid of any form of timebaie output.
CONSTRUCTION
The prototype is housed in an ,,A.8.S." case type M3, obiainabi6 from Doram ei".tt"r-i.r,'f,ta. fnl"s'is
a plastic case with metal front panel and -earu.".
130,by-100 by 50ln[r Fig. 2 shows the holes required
rn the tront,panel. The two small mounting hol-es for each c<.raxial socket are marked out with the"aid of the
socket itself TtgV are drilled 684 clear with a No. gi
twrst drrll. A solder tag is fitted under the inner secur_ ing.nut of the timebase output socket, SK2, to provide
a chassis connection.
All the small components are mounted on a
Veroboard panel of 0.1ih. matrix,,this having t3 holei Dy Ib copper stnps. I'here are no breaks in the strips.
USING THE GENERATOR
As alreadv mentioned, the timebase outl[lt
connects to thl timebase input of the wobbulator' The
irigger pulse output connects, where applicable, to the
tri[[er'input <-ti"the oscilloscope. The equipment,i's
then set up in rnuch the same. way as qltn tne woobulator
on its own, except that lt ll no^w also necessary
io aajust the frequeniy control of.the additional
timebase. The frequency is set up such that one comnlete
picture of thi disilayed reieiver passband fills,
hr neirly fills, the osiilloscope screen from side to
side.