IEC 61843:1997 pdf download – Measuring method for the level of intermodulation products generated in a gyromagnetic device

IEC 61843:1997 pdf download – Measuring method for the level of intermodulation products generated in a gyromagnetic device.
IEC 61843 describes the measuring method for the level of intermodulation products generated in a gyromagnetic device.
When two or more signals of d,fferent frequencies enter into a device andor equipment having non-linear characteristics (contact point, flexible waveguicie. ferrite device, etc.), harmonics are generated in that device and/or equipment. Moreover, differential or added frequencies occur in the device due to mixing of harmonics or a harmonic and the fundamental frequency. These resultant frequencies create noise causing interference.
In transmitter/receiver duplexirig systems and radio relay systems, many frequencies are allocated to a specified band so that combinations of transmitting frequencies and harmonics may fall on the receiving band. This causes deterioration of communication quality due to intermodulation.
Since the intermodulation interferences cannot be prevented by tittering, it is important to evaluate the Intermodulation products level of the device to be employed In such a system.
2 Principle of measurement
When a number of different frequencies, denoted by subscript i. exist, intermodulation frequency (f) is represented as follows:
where n1. n2 n1 are integers.
Since, in many cases, third order intermodulation products are the most probable, the
measuring method for third order intermodulation will be described hereinafter.
Two signals of specified power levels and frequencies (ii and 12) are combined utilizing a power combiner.
The residual intecmodulation product (2f1 — ‘2 or 2(2 — I) of the measuring system by connecting the combined signal directly to receiver should be less than —90 dBm.Then the intermodulation product of device under test is determined by connecting the device between the signal source and receiver.
3 Measuring arrangement
The measuring arrangement is shown In figure 1.
It comprises two generators with specified power levels and frequencies, a power combiner, a low-pass filter, band-pass filters, a receiver and other components.
3.2 Directional couplers
3.2.1 Directional couplers l, 2 and 3)
These couplers are used to provide partial power from the generator to the frequency meter and the power meter for monitoring.
3.2.2 Directional coupler (4)
This coupler is used to reduce the power entering the receiver and to suppress the influence of fundamental signal reflection from the band-pass filter 3.
3.3 Frequency meters (I and2)
These trequency meters are used to monitor the frequencies of the generators.
A resonant cavity type wave meter or digital frequency counter is recommended,
3.4 Power meters
3.41 Power meters (1 and2)
These power meters are used to monitor the power levels of the generators.
3.4.2 Powee’ meter (3)
This power meter is used to set the output level at port A.
3.5 Band• pass filters
3.5.1 Band-pass filters (1 and2)
These filters are used to eliminate unwanted spectra of the fundamental signals. Attenuation of 40 dB or more is required in the out of band range.
3.9Receiver
lt comprises a low distortion down converter，a low-noise high gain wide dynamic rangeamplifier and a display section.A spectrum analyzer with a noise level less than -100 dBm anda third intermodulation product less than -100 dB is recommended as the receiver.
4Measuring procedure
a) Adjust the frequencies of the two generators to specified ones with the aid of a frequencymeter.
b) Connect port A to port B directly and adjust the power level of the generators individuallyto specified levels using the variable attenuators (1 and 2).During the adjustment,theremaining generator should be turned off to ensure proper setting.
c) Connect port A to port Cdirectly，and measure the intermodulation product atfrequencies of 2f- f2 and 2f.
When the product is larger than -90 dBm,try to reduce the product by means of fasteninguncertain contacls and exchanging components, if necessary.
d) Connect the device under test between port A and port C, and measure theintermodulation products on the display of the receiver.
5 Expression of results
The results are expressed in decibels referred to one milliwatt (dBm) for the frequencies andlevel of source signal.