Fig. 5-3. Location of discriminator output lead.

TM 11-6625-3017-14

Output Attenuator:

30 or 40 dB.

frequency; the frequency blip will then be shown on the

Sweep Width control:

maximum sweep.

Polyskop. It is advisable to adjust the Polyskop

Centre Frequency

frequency control and the OSCILLATOR TUNE control

control:

mid-way.

together, so that the correct frequency blip remains on

Y1 Gain control:

maximum gain.

the screen.

Y1 switch:

Y2 switch:

off.

(7)

If the sensitivity at any min is below that specified,

adjust capacitor A2bC7 and the position of the

Set the TF 2300 controls as follows:

tuning slug in coil A2bL2 to increase the amplitude

where the frequency blip is a minimum. It may also

SUPPLY:

on.

be necessary to select a new value for A2bC14.

Oscillator RANGE:

RANGE 5 - 8.

CRYSTAL:

OFF

NOTE:

Capacitors C7 and C14 will need to be set

(4)

Adjust the OSCILLATOR TUNE control to about 88

to a compromise position to give the best sensitivity

MHz on the tuning scale, i. e. A local oscillator

throughout the frequency range, as there will be more

frequency of 22 MHz.

than one minimum sensitivity point. Sensitivity becomes

approximately correct if the input attenuator on the

(5)

Set the Frequency switch on the Polyskop to about

Polyskop can be set to the 30 or 40 dB position. While

50-100 MHz and the Frequency Markers switch to

the checks are being carried out, note that no spurious

50 MHz.

oscillations occur.

The Polyskop screen will show a sweep between 50

and 100 MHz with the 50 MHz marker pips at each

5.4.6

De-emphasis

end of the trace.

Test equipment: j and k

The 88 MHz signal, i. e. 4th harmonic of the 22 MHz

from local oscillator, will show as a double blip at 88

(1)

With the modulation meter switched off, disconnect

MHz on the trace. Tune the local oscillator over the

the yellow lead from the discriminator unit output

frequency band, i. e. increase frequency and the

(A5, pin 4) and connect the lead to the output of the

frequency blip on the Polyskop should move

signal source.

towards the 100 MHz marker.

Range 5 on the TF 2300A covers 88-176 MHz;

therefore, when the 100 MHz blip reaches the 100

MHz marker, change the Frequency switch on the

Polyskop to 100-200 MHz and the 100 MHz blip will

appear superimposed on the 100 MHz marker at

the beginning of the trace. Continue to tune through

the range to 176 MHz:

(6)

Then tune the local oscillator through the remaining

frequency ranges up to 1000 MHz and note the

frequencies at which the frequency blip shown on

the Polyskop is a minimum and measure the

sensitivity at these points using the signal generator

and the R. F. millivoltmeter.

NOTE:

When using the Polyskop above 400 MHz,

the variable frequency control must be set to the required

frequency and the OSCILLATOR TUNE control on the

TF 2300 should be tuned to this

Fig. 5-3. Location of discriminator output lead.

5-6