11.2.7
USING HARMONIC RELATIONSHIPS TO
CALIBRATE VARIABLE FREQUENCY
GENERATORS
11.2.7.1 To illustrate this procedure assume that it is
desired to calibrate a generator at 22.5 MHz.
11.2.7.2 With the FUNCTION switch of the Model
415 in the IF position, select the 45 MHz
marker. Tune the variable generator to an
indicated 22.5 MHz point while observing
the oscilloscope trace. As the 22.5 MHz fre-
quency is approached a marker correspond-
ing to the second harmonic of the generator
frequency will appear on the oscilloscope
trace.
Once again, the generator is adjusted until
a zero beat occurs between the 45
MHz
marker of the Model 415 and the second
harmonic of the variable generator. This
indicates that the variable generator is ad-
justed to exactly 22.5 MHz.
11.2.7.3 Using the same principles a variable fre-
quency generator can be calibrated at 90
MHz by adjusting the variable generator
output until the generator marker coincides
with the 45 MHz marker of the Model 415.
In this case what is happening is that the
2nd harmonic of the 45
MHz signal of the
Model 415 is beating against the 90
MHz
signal from the variable generator. This
general procedure can be used with 3rd and
4th harmonics as well as the 2nd harmonic
method illustrated here.
11.3
AM BROADCAST RECEIVER TUNING AND
TRACKING CHECKS
11.4
11.4.1
82
Because the Model 415 has crystal con-
trolled signals available at the output when
used in the MKR or MOD MKR functions,
the combinatipns of these marker frequen-
cies can be used to generate difference
frequencies which fall in the AM broadcast
range. For example, by using the 41.67
MHz and 42.17 MHz markers, a difference
frequency of 0.5 MHz is generated and is
amplitude-modulated if the MOD MKR func-
tion position of the Model 415 is used. Using
41.67 and 42.67, a l MHz crystal controlled,
amplitude-modulated signal can be gener-
ated. Repeating the procedure, combining
39.75 MHz and 41.25 MHz a difference fre-
quency of 1.5 MHz is obtained. This pro-
cedure can be used in the broadcast band
as well as in short wave bands using other
frequency differences. In addition, multiples
of the marker crystal frequencies can be
used as outlined earlier to generate addi-
tional crystal controlled reference frequen-
cies.
ADDITIONAL USES OF THE MODEL 415
As previously mentioned, multiples of the
basic sweep frequency ranges can be used
for sweep frequency checks in frequency
bands other than the basic 10. 7 MHz and
the television i-f frequency range. Any of
the 10. 7 MHz harmonics can be used for
sweeping at frequency multiples of 10.7
MHz. Because harmonics are used, this
means that the maximum sweep available
at the fundamental 10.7 MHz sweep range
is multiplied by the order of the harmonic
being used. For example,
if the 3rd har-
monic of the 10.7 MHz sweep is being used
for alignment in the 30 MHz region then the
maximum sweep would be 3 times that
available at 10.7 MHz or over 6 MHz. The
100 KHz markers, when used, would repre-
sent frequency intervals of 300 KHz in this
case.
11.4.2 The swept video output of the Model 415
can be used for direct-sweep frequency
evaluation in the 1 to 6 MHz range. The
output is essentially flat over this frequency
range. As with the other frequency outputs,
harmonics of the video sweep can be used
for sweeping at multiples of the basic
1 to 6
MHz range. Once again, the internally gen-
erated markers of the Model 415 can be
used for frequency checks. For example,
the 41.25, 41.67, 42.17, and 42.67 markers
can be read directly as 4.5, 4.08, 3.58 and
3.08 respectively. Also, any other marker
can be used for frequency identification in
the video sweep range by subtracting the
indicated frequency from the pix frequency
which is 45.75
MHz. For example, if the 44
MHz marker is energized while using video
sweep the marker can be interpreted as
45.75-44.00
= 1.75 MHz. This applies to all
other marker frequencies as well.
When using multiples of the basic video
frequency the indicated marker frequency
must be multiplied by the harmonic of the
video sweep being used. As an example,
if the 2nd harmonic of the video sweep is
being used for response checks in the 2 to
12 MHz region, the indicated marker at 4.08
MHz will actually be 8.16 MHz or twice the
indicated frequency.
11.4.3 When using modulated marker outputs or
unmodulated outputs of the Model 415 for
performing receiver tracking checks for cal-
ibration purposes it is not always necessary
to make a direct connection to the receiver
under test.
If a short lead is connected to
the yellow lead of the
RF cable terminating
pad this acts as an antenna and can be
used to radiate the test signal to the re-
ceiver under test by placing it near the
receiver.
The above miscellaneous applications of
the Model 415 are intended to demonstrate
the versatility of the Model 415 in applica-
tions other than television receiver align-
ment. We are sure that the user will devel-
op additional uses for the Model 415 as he
becomes increasingly familiar with its fea-
tures and its operation.
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