McIntosh MI 2 Owners Manual

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MI-2 MULTIPATH/TUNING INDICATOR GENERAL DESCRIPTION The Mclntosh MI-2 Multipath/Tuning Indi­ cator is designed to be used with an FM tuner to detect and display multipath reception. Multipath reception is the result of a reflected signal arriving at the tuner antenna slightly later than the direct signal. By rotating or repositioning your FM antenna it is possible to reduce the multipath reception. The MI-2 Multipath/Tuning Indicator makes it easy to know when the FM antenna is oriented for the best reception of any station. Multipath reception degrades FM tuner performance in several ways: 1) Usually there is an increase in back­ ground noise level. 2) Distortion is often heard in the pro­ gram signal. 3) Stereo separation may be reduced. 4) The stereo effect may be completely lost. 5) Stereo indicators may fail to function, or function erratically. Figure 1. FM Tuner Antenna Receiving Direct and Reflected Signals To show multipath reception the MI-2 dis­ plays instantaneous signal strength versus frequency deviation. Signal strength is shown as vertical deflection of the indicator display beam. Frequency deviation is shown as hori­ zontal deflection. Multipath reception ap­ pears as a peak or a valley in the MI-2 dis­ play. See Figure 2. To overcome multipath reception it is usually necessary to orient the tuner antenna to receive the FM signal by only one predom­ inant path. Rotating a directional antenna is very effective at correcting multipath recep­ tion. In a metropolitan area where a simple antenna such as a dipole is used reposition­ ing the antenna will achieve the same result. 1 DIRECT SIGNAL REFLECTED SIGNALS

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(2a) (2 b) (2c) (2d) Figure 2. Various Forms of Multipath Reception As They Appear on the MI-2 Display Screen. Such a change may be as little as a fraction of a foot or as much as several feet. The MI-2 is also a very effective tuning indicator: 1) Signal strength is shown by the vertical position of the display trace. The higher the position of the trace the greater is the signal strength. 2) Correct tuning occurs when the display trace is centered horizontally on the screen. Since the display trace effec­ tively follows the tuner I.F. response curve, centering the trace tunes the detector to the center of the I.F. curve. The Mclntosh MI-2 Multipath/Tuning Indi­ cator is a versatile instrument. Its usefulness has been extended to show other signal volt­ ages. By turning the SCOPE TEST switch to the L & R AUDIO position the MI-2 shows the stereo or monaural character of the audio signals). 1) A trace display along the L+R line will occur with a monaural program source. 2) A trace display along the L-R line will occur with a monaural program source if the phase of one channel is reversed. 3) A vertical trace indicates that the pro­ gram is being delivered to the left channel only. 4) A horizontal trace indicates that the program is being delivered to the right channel only. 5) Operating the balance control on your tuner-preamplifier or system preampli­ fier can change the slope angle of the L+R or L-R display. 6) A stereo program will be a complex and varying circular or elliptical display of irregular outline that depends on chan­ nel separation or on the phase ampli­ tude relation of the Left and Right channel. 2