This is an useful and cheap test equipment for beginners. The poor
lowfer level
generator and not selective level meter choice.
If you pay no more than 50 Euro for it you buy:
one 30 Hz to 550 kHz signal generator with output attenuator,
Zout 75 or 600 ohms unbalanced and 150 or
600 ohms balanced, adjustable from 0 to -70 dBm (in 1 dB steps), with
dedicated monitor level meter, AC and DC volt meter
one wide band level meter (not selective), Zin 75 or 600 ohms
unbalanced and 150 or 600 ohms balanced, sensitivity from +20 to
-60 dBm in 10 dB steps (useful up to -70 dBm)
one low level amplifier
The goodies:
oscillator very stable, low harmonics content
accurate attenuator
accurate level meter
The bads:
old style, it use some germanium transistors
low quality rotary switches, they needs some cleanings with spray
contact cleaner
compressed frequency dial redout but with fine tune vernier, for
136
kHz is better to use an external digital frequency meter
the generator level, in spite of the attenuator, change if the
load
impedance change (but the attenuator level meter shows the variations)
requiring an adjustment of the "Set Output" knob
WARNING: the 230V main supply wiring
insulation
may be damaged. Inspect carefully and replace all the damaged wires
I use this equipment for LF filters alignment, antennas Q
measures, as RF resistance bridge generator and detector and as general
purpose audio test set.
Application example: measuring antenna Q using a low and adjustable
level
beacon.
This procedure allow to measure the antenna Q. For receiving loop
antennas connect to the level meter input the antenna
preamplifier output.
Wind about 100 enameled wire turns on a ferrite road.
Connect
the
winding to the attenuated oscillator output using a twisted pair.
Put the ferrite road few meters far from the antenna under test.
Select 150 or 600 ohms balanced load impedance output.
Connect the LF receiving antenna to the level meter input, using
a
low-pass filter if you have overloading from
LF/MF broadcasting. The meter should not read more than -50 dBm.
Tune the oscillator frequency to 136.000 kHz (center frequency, Fc).
Use a digital
frequency meter.
Adjust
the receiving antenna system for maximum level.
Adjust the oscillator level for about -30 dBm at the
level meter.
Now verify test setup
for linearity and interferences: decrease the oscillator
level by 10 dB and verify on the level meter for an equal 10 dB change.
Tune the frequency up and stop when you see a -3 dB variation on
the level
meter, note this frequency as Fhigh, in kHz.
Tune the frequency down and stop when you see a -3 dB variation
on the level
meter, note this frequency as Flow, in kHz.
