In many radio and audio applications, oddorder imps are of most interest, as they fall within the vicinity of. Odd orders of inband mixing frequencies produce some inband products, but when outofband mixing frequencies are involved, evenorder products may fall in band. Intermodulation im or intermodulation distortion imd is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities. The distortion can be represented as a set of individual evenorder, 2nf, and oddorder, 2n1f, components. Rouphael, in rf and digital signal processing for software defined. Intermodulation interference most often concerns odd order products. Third order intermodulation products of the two signals, f1 and f2, would be. Finding, solving and preventing intermodulation problems. It does this by testing for odd andor even order products caused by the mixing of multiple transmitters at a given site in a nonlinear device. Buy midian electronics intermod intermodulation product.
The intermodulation between each frequency component will form additional signals at frequencies that are not just at harmonic frequencies integer multiples of either, but also at the sum and difference frequencies of the. This intuitive tool guides the user through four simple steps to efficiently configure the instrument to measure oddorder intermodulation products 3rd, 5th, 7th. Therefore, the odd order intermodulation products cannot be removed by filtering, only by improvement in linearity. The analysis only considers inband modulation products. Generally the 7th and 9th orders are too weak to cause intermodulation interference. The odd order products, however, produce signals near the input frequencies f 1 2f 2 et f 2 2f 1. Rf calculator conversion from and to various rf units intermodulation calculate intermodulation for 2 and 3 frequencys up to the 9th order. In 4 the relative strength of second and third order intermodulation distortion imd was shown to vary.
Note that one third order product 2f 1 f 2 is only 1 khz lower in frequency than f 1 and another 2f 2 f 1 is only 1 khz above f 2. The first and last sum products are unique where the first product location is. Understanding intermodulation distortion measurements. Synchronous, or same frequency, measurement of both even and odd order distortions permits quantitative. It can be a tremendous job to calculate the intermodulation products from several frequencies, below is a calculator that calculates the intermodulation product from two and three frequencies. The former are due to asymmetric nonlinearities of the transducer, while the latter are due to symmetric nonlinearities. In many radio and audio applications, oddorder imps are of most interest, as they fall within the vicinity of the. The oddorder difference frequencies are the most important.
This article will focus on linear, secondorder and thirdorder terms, although the analysis is similar for higherorder terms. Oddorder intermodulation products fall inband, with sidebands close to the carrier. Please notice how the signal level diminishes as the odd order increases. Further computer and empirical evaluation of these.
Rf blockset formerly simrf provides a simulink model library and simulation engine for designing rf communications and radar systems rf blockset lets you simulate nonlinear rf amplifiers and model memory effects to estimate gain, noise, even order, and odd order intermodulation distortion. One third order product 2f1f2 is 1 khz lower in frequency than f1 and another 2f2f1 i is 1 khz above f2. Esp audio pages intermodulation distortion things you didnt know. These affect the signal in such a way that the desired signal strength is reduced.
Intermodulation im or intermodulation distortion imd is the amplitude modulation of signals. The frequencies of intermodulation products are equal to sums and differences of the different frequency components in the input signal. Intermodulation distortion is one of the most interesting signal analyzer measurements. Rf intermodulation calculator,formula for rf intermodulation. Third order intermodulation products of the two signals, f. Therefore, with symmetrical distortion, any imd products are limited to oddorder effects only. Hauppauge, ny intermodulation interference is typically calculated based on two signals present in the rf or if bandwidth. Intermodulation interference calculations in the land. How to perform a nonlinear distortion analysis of a. Like thirdorder distortion in amplifiers, mixer spurs can end up close to or on top of the. Both even and odd orders of nonlinearity can arise, but from different physical origins.
Even and odd order intermodulation nonlinearity from superconductive. The level of interference is related to the system nonlinearity which can be defined by the theoretical intercept points for each higherorder nonlinearity e. Compared to other intermodulation products, oddorder intermodulation products created within a receiver are of particular interest because the oddorder product of two signals in the. However, intermodulation products can be easily seen in the frequency domain. Intermodulation product an overview sciencedirect topics. April, 1994 5 6 3 4 2 the intermodulation distortion imd performance of 1 wideband, dccoupled amplifiers is a relatively new area. Reviewing the basics of intermodulation distortion.
It includes features you wont find in any other product including those that cost many times more. The interference due to intermodulation is defined by the following equations. Intermod assist intermodulation calculator and frequency coordination software is a unique tool it will change the way you approach the problem of intermodulation interference and the challenges of frequency coordination and channel assignment. Radio mobile rf propagation simulation software on.
Intermodulation im or intermodulation distortion imd is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities in a system. Odd order, rather than even order, intermodulation distortion products are of concern in linear power amplifiers because they are relatively close in frequency to the desired signal. Visible intermodulation products are seen as small spurs at 280 mhz and 265 mhz. It is generated when two signals are applied to a nonlinear device. Thus, both ctb and cso will show an increase when clipping happens with sufficient frequency to be. The toi products are usually within or close to the useband, i. Intermodulation distortion occurs at frequencies that are the sum andor difference of integer multiples of the fundamental frequencies. Any frequency on the left is always greaterthanorequalto any frequency to its right. The most common interference are the 3 rd and 5 th orders. Testing ham radio hf linear amplifiers can be done by injecting a two tone test signal usually 700 hz and 1900hz into the amplifier input and observing the modulation envelope with an.
One fifth order product 3f12f2 is 2 khz below f1 and another 3f22f1 is 2 khz above f2. The most critical intermodulation distortion product is the third order intermodulation toi product. Order of product the sum of the absolute value of coefficients of all components of predicted intermodulation product. Wb6noa gordon wests, extra class license preparations. Pdf even and odd order intermodulation nonlinearity from. The above equations are valid for steady carriers, and it is easier to understand the concept of intermodulation by using them. Looking carefully at the table, we see that only the odd order intermodulation products are close to the two fundamental frequencies f1 and f2. This is the ratio of the carrier power to the spurious 5th order intermodulation power in db.
In order to provide such a clean result set prfintermod enforces some restrictions as it calculates hits. The definition of the thirdorder intermodulation given in equation 9 is the same as for tones used to describe intermodulation distortion in narrowband analysis. When the bandwidth is less than an octave, evenorder intermodulation products, such as second and fourthorder intermodulation. Such is the case in differential amplifiers where the transfer function exhibits oddsymmetry. The intermodulation colocation software then screens the potential intermod interference threats against preset system intermod interference thresholds. Symmetrical distortion means that there are only oddorder harmonics even order. In this paper we have proposed a solution to overcome this, which can be implemented if the check for spurious if is made with. Intermodulation interference most often concerns oddorder products. Three sequences describe the frequency sum products.
Technical feature topics in communication system design. When that occurs, intermodulation products are generated. This is the power of the spurious 5th order intermodulation signal in dbm units, measured with the spectrum analyzer. Intermodulation measurements on rf amplifiers rohde. The higher the thirdorder intercept level, the better the receiver.
It is simple to find the input amplitude where the distorted. Intermodulation from high power broadcast transmitters is a special case. Interaction of intermodulation products between dut and. The fifth order product is also closer to the fundamentals than. Calculate intermodulation products from 2 and 3 frequencies. From the table it becomes apparent that only the odd order intermodulation products are close to the two fundamental frequencies of f1 and f2. Symmetrical distortion means that there are only oddorder harmonics even order harmonics are suppressed cancelled. Online calculators this website offers a collection of online rf tools. It is quite easy to see this effect in the graphic below. A frequency spectrum plot showing intermodulation between two injected signals at 270 and 275 mhz the large spikes. The thing is that the sound containing evenorder harmonics is perceived as sweet and warm. Compared to other intermodulation products, oddorder intermodulation products created within a receiver are of particular interest because the oddorder product of two signals in the band of interest is also likely to be within the band. Midians intermod calculator predicts the possible occurrence of intermodulation products that may cause receiver interference at the radio repeater site.
Intermodulation calculator intermod study software. With this technique the surface current density of both the driving signal and the imd tones can be quantified. Rf frequency selectivity parameters at frequency deviations f 1 and f 2 from. The intermodulation products are sum and difference as well as other integer and non integer multiple of these frequencies.
Basically, 3im is produced by the mixing of the 2nd harmonic or overtone of one tx signal with the fundamental 1st. Some people have worked around this by horn loading the driver for low frequencies, but bass horns are. In many radio and audio applications, odd order imps are of most interest, as they fall within the vicinity of. Midians intermodcalculator predicts the possible occurrence of intermodulation products that may cause receiver interference at the radio repeater site. Higher order products are potential sources of intermod which cannot be ignored, because they also fall on inband frequencies. Preventing desensitization of radio frequency receiversa. This intuitive tool guides the user through four simple steps to efficiently configure the instrument to measure oddorder intermodulation products 3rd, 5th, 7th and 9th and calculate the associated intercept points. A method has been developed that uses three input tones to measure both even and odd order intermodulation distortions imds inside the pass band of resonant devices.