RADIOMETER AFM 3, Manual

Page: 23 / 107

14) Read the modu lotion deviation.
Check whether the reading is the same
for both peaks of modu lotion: a dif­
ference indicates distortion of the mod­
u I at ion envelope. See Fig. E4, and
refer to SECTION B - SPECIFICATIONS
under "FM MODULATION - Distortion''.
Residual FM on CW and AM signals
Proceed as described immediately above.
Because of the very effective I imiter
stages in the FM detector, the residual
FM caused by amplitude modulation is
quite low, viz. 25 Hz (r.m.s.) when
the band-pass fi Iter (50 Hz - 15 kHz)
is used. The residual FM at a carrier
frequency with in 6 - 200 MHz is less
than 25 Hz FM (r.m.s.), and less than
100Hz FM (r.m.s.) up to 1001 MHz,
when measurements are performed in a
room with an acoustical noise level
lower than 60 dB (rei. 2 1 o-4 1-1bar)
and the band-pass fi Iter (50 Hz - 15
kHz) or one of the deemphases (50
!JS
or 75
!JS)
is used. When the 0.3 - 3
kHz band-pass fi Iter or the 750
!JS
deemphasis is used, the residual FM is
8 Hz FM (r.m.s.) within the frequency
range 6 - 200 MHz, and less than 30
Hz FM (r.m.s.) up to 1001 MHz for
the noise level specified above. (See
SECTION B - SPECIFICATIONS.)
If a resolution somewhat higher than
that corresponding to the 1 kHz devia­
tion range is wanted, an electronic volt­
meter can be connected to the AF OUT­
PUT terminals. The external meter wi II
read 1 volt for full deflection of the
internal meter, i.e., with the METER
switch set to 1, the deviation read on
E4
Fig. E5. The arrows show screws and
plate to be removed when a plug-in
unit is to be used.
the electronic voltmeter will be 1 Hz
per mV.
USING A CRYSTAL OSCILLATOR PLUG­
IN UNIT, CODE 900-252
1) Remove the two screws and the plate
covering the receptacle ' in which the
Crystal Oscillator Unit is to be placed
(see Fig.E5).
2) Supply the Crystal Oscillator Unit
with crystals. Bear in mind that the
crystals must have the frequency fer
defined below�
f
==
cr
f - 1
s
2n
MHz
where fs indicates the carrier frequency
and n the odd harmonic of the crystal
overtone frequency. The sensitivity spec­
ifications (see item INPUT LEVEL in
SECTION B - SPECIFICATIONS or
Fig. E6) are based on the combinations
shown below of carrier frequency, order
of harmonic, and range of crystal fre­
quencies.
Carrier frequency Order of harmonic Range of crystal frequencies
f
n f
s cr
200 - 600 MHz 3 33 - 100 MHz
600 - 1000 MHz 5 60- 100 MHz