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.
