Manual FCKL 1528 page - 17
11 Optional Tracking Generator
11.1 What is it good for?
The optional tracking generator produces a signal on a frequency which is equal to the
receiver frequency. Transmitter and receiver come together as a transceiver. Being on the
same frequency all the time makes tuning and measuring very easy and fast.
11.2 How does it work?
The input frequency of the receiver is mixed several times until the audio frequency band
is reached. The tracking generator does the same in the opposite sense, it mixes
frequencies until the final frequency is reached, which is equal to the receiver frequency.
Additional filtering and amplification give a strong (1V/50
Ω
) clean signal.
11.3 What is it good for?
Tracking generator and interference measuring receiver together are a powerful
instrument to measure attenuation. This is due to the sensitivity, the dynamic range and
attenuator precision of the receiver. If as in this case the output voltage of the tracking
generator is high (1 V/50
Ω
), in theory attenuation of more than 130 dB can be measured.
In the real life such attenuation has to be measured not very often and measurement is
critical because of the decoupling needed. On the other hand, the high dynamic range
available can be used to put in fixed attenuators to improve matching, which improves
precision.
11.4 Which are the most important tasks?
11.4.1 Filter measurement
While a part of the interface is already suppressed on the PC-board where it’s produced,
usually additional filtering is needed in the power supply lines. This filter prevents
conducted interference to spread via the mains cable. Filter attenuation is most often
given by the manufacturer’s data sheet, but it is very helpful to check it in the assembly.
This can be done by connecting receiver and tracking generator to the filter’s input and
output. The level difference is the filter attenuation on the frequency tuned.
11.4.2 Field attenuation between transmitting and receiving antenna.
The attenuation between 2 antennas in a free field area can be calculated, but especially
in non perfect areas differences occur. They can be recorded, when transmitting and
receiving antenna are connected to the tracking generator and the receiver. In the
frequency range from 9 kHz-30 MHz a passive magnetic loop antenna is usually used for
transmitting and a magnetic field strength adapter for receiving. It is now possible to
record the attenuation via the frequency and check the differences to the calculations. In
the same way the effectiveness of shielding and shielding rooms can be measured.
11.4.3 How to calculate the attenuation?
Attenuation [dB] = Transmitting Level [dB
µ
V] - Receiving Level [dB
µ
V] - Additional Attenuation [dB]
The transmitting level of the tracking generator is 120 dB
µ
V.
The receiving level is measured as usual.
Additional attenuation can be 10 dB fixed attenuators on the output of the tracking
generator and on the input of the receiver.
Also antenna factors and other transducer factors and attenuation have to be considered.