30
Due to the curved characteristic of m ix i ng diode 409 l ow-frequent difference signals appear as so'on as the
frequency of the h.f. osc i l l ator approximates to one of the frequenc ies of the ca l ibration oscil lator o r its
harmonics.
The difference frequencies are suppl ied to the I.f. amplifier and lim iter 324 v ia low-pass filter 770/552 (cut-off
frequency about 25 kHz).
3_ 1 _ 6.3. L. F. amplifier, limiter and indicator
The band-pass
curve
of I .f. amplifier 324 as
a
function of the h.f.
signal
is represented in F ig. 28.
The gain and thus the adaptation to the input signal is determ i ned by resistor 655.
The output stage of th is i ntegrated circuit can be overloaded easily . The cut-off frequency is decreased with
capacitor 557. At the col lector of tra nsistor 3 1 3 a square-wave signal is avail able which contro l s transistor 3 1 3,
fu nctioning as a switch, in such a way that capacitor 561 is discharged periodica l l y .
The charge is complemented v i a ind icator 8 1 5 and resistor 660. The indicator deflects i f there is a difference
frequency. If the d ifference frequency is zero or very sma l l - if the h .f. signal equals one frequency of the
ca l ibrator or only sl ightly deviates
-
the
frequency
is
suppressed by
the I .f. ampl ifier a nd the i nd icator w i l l not
deflect. The same applies if the difference frequency of the m ix ing product is outside the band-pass cu rve of
the I.f. ampl ifier. Thus the equality of h .f. and one of the cali bratio n frequencies can be recognized by a c lear
minimum between two maxima.
The places where a "zero-i ndication" may be expected du ring ca l ibration are indicated by sma l l triangles on
the corresponding scal es.
I f button CA L is not depressed, the i nput of the I.f. amplifier is bl ocked via diode 4 1 5 and resistor 679 .
f
I-1F >
I
CA
MA
8204
Fig.
28_
Band-pass curve indicator
3. 1 .7. RAN G E I N DICATION
The six l ight-emitting diodes 49 1 ... 496 on unit 3 serve to indicate the frequency range used .
Synchronously with the range switching of the h.f. oscil lator, one of the LE D's is switched on via resistor 60 1
(on unit 3) and a combination of switches of u n i t1 .
3. 1 .8. SUPPLY
The plus potential of the - 1 2 V and - 1 8 V supply a re connected to ci rcuit zero. Both sources are stabil ized.
The unstabilized voltages are produced by rectifier 405 on unit 2. The output voltage, d iv ided by resistors
637/638/639, is compared with the reference voltage across zener diode 404 via operational ampl ifier 322.
The output voltage of operational amplifier 322 contro ls series transistor 3 1 1 via current amp l ifier 3 1 2 .
The offset-voltage of the operational ampl ifier is reduced b y resistor 64 1 . The short-circu it cu rrent of the - 1 2 V
supply is l imited by resistor 645.
The stabilizing circuit for the - 1 8
V
supply is the same as given for the - 1 2 V supp ly. The reference voltage is
the - 1 2 V supply. The output voltage is compared with the reference voltage via vol tage d ivider 635/636.
A separate secundary wi nding of the mains transformer suppl ies the vol tage for the sca le il lumination ( lamps
8 1 1 ... 8 1 3) a nd for the il lumination of the indicator via switch 803/1 A ( button CAL).
Summary of Contents for PM5324
Page 1: ...HF Generator 100kHz 110MHz PM5324 9452 053 240 1 9499 450 05511 730801 1 01 ...
Page 15: ...14 Fig 4 Front view Fig 5 Rear view ...
Page 43: ...Fig 33 Front view with item numbers Fig 34 Bottom view ...
Page 44: ...44 Fig 35 Top view Fig 36 Left side view ...
Page 45: ...45 0 0 0 0 1 ji I I MAB225 Fig 37 Scale dri ve n ...
