HP 400E, Operating And Service Manual

Page: 15 / 57

ModeI400E/EL
BATTERY VOLTAGE
+
35-55
JL
35-55
VDC
VDC
+
11-
B2 Bl
(35-55V)
(35-55V)
400E/EL-B-0461
Figure 3-1. External Battery Connection
e. Connect signal to be measured to INPUT
terminals, and read the rms voltage on the
scale.
3-9. DB Meter.
a. To make a dB or dBm measurement, follow
steps a through e in Paragraph 3-8, and add
the scale reading to the RANGE setting. For
example: If the scale reading is +
I
.5 and the
RANGE is -30dB, the final measurement is
-28.SdB.
b. The 400E/EL dB scale is calibrated in dBm.
OdBm is equivalent to
I
milliwatt dissipated
by a 600 ohm load. Consequently, any dBm
measurements must be made across a total
impedance of 600 ohms. Measurements
across other impedances will
be
in dB, but
not dBm.
c. To convert a dB reading to dBm, use the
Impedance Correction Graph (Figure 3-3).
For example: To convert a +30d B reading
made across 50 ohms to dBm, locate the
load impedance on the bot tom of the graph.
Follow the impedance line to the heavy
black line and read the meter correction at
that point. The correction for 50 ohms is
+1O.SdBm, and the corrected reading is
+40.SdBm.
Section
III
3-10. Ac to Dc Converter.
a. Follow steps a through e in Paragraph 3-8.
b. Connect the rear panel DC OUTPUT
terminals to a dc measuring device with a
high input impedance. The dc output
resis tance is 1000 ohms; and if it is loaded,
the dc output signal will be inaccurate.
c. The dc output is a 0 to
I
volt Signal
proportional to the percentage of 400E/EL
meter deflection.
3-11.
Wide Band Ac Amplifier.
a. Follow turn·on steps a through c in
Paragra ph 3-8.
b. Select approximate range of input on
RANGE switch.
c. Connect SIGNAL to be amplified to INPUT
terminals.
d. When using an ac power source, ground
loops can be eliminated by connecting the
400E/E L to an adequate isolation transf­
former. This will open the power line ground
circuit as shown in Figure 3-3.
Figure 3-3. Isolation Transformer.
NOTE
Place a
I
kilohm shielded load
across the DC OUTPUT, if it is not
being used, when using the AC
O UT P UT. Thi s i s especially
necessary on low ranges.
e. The gain of the amplifier depends on the
RANGE selection. On the 0.1 volt range and
below, the 400E/EL a mplifies the input; and
3-3