Marconi TF2333 MF transmission measuring set
By Claudio Pozzi, IK2PII - April 2004
This is an useful and cheap test equipment for beginners. The poor
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
- oscillator very stable, low harmonics content
- accurate attenuator
- accurate level meter
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.
- old style, it use some germanium transistors
- low quality rotary switches, they needs some cleanings with spray
- compressed frequency dial redout but with fine tune vernier, for
kHz is better to use an external digital frequency meter
- the generator level, in spite of the attenuator, change if the
impedance change (but the attenuator level meter shows the variations)
requiring an adjustment of the "Set Output" knob
- WARNING: the 230V main supply wiring
may be damaged. Inspect carefully and replace all the damaged wires
Application example: measuring antenna Q using a low and adjustable
This procedure allow to measure the antenna Q. For receiving loop
antennas connect to the level meter input the antenna
- Wind about 100 enameled wire turns on a ferrite road.
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
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
the receiving antenna system for maximum level.
- Adjust the oscillator level for about -30 dBm at the
- 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
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.
- Compute the Q of
your's antenna system: