Learning Event 4:
DESCRIBE AND IDENTIFY PHASE SHIFTING AND DISTORTION PROBLEMS IN STEREO
SYSTEMS
1.
Importance of alignment. Accurate and precise head alignment is very important in terms of a
stereo tape deck.
a. Azimuth misalignment between the record and playback heads, or from a different skewing
of the tape during the record and playback modes, will result in phase shifting between channels.
Because of this shifting, compatibility and interchangeability are much harder to obtain for stereo tapes
than for mono tapes.
b. Therefore, this type of distortion is more evident when reproduced on a monophonic
receiver. Keep in mind that monophonic receivers basically reproduce the sum of the two channels.
Any phase shifting between these two channels differs with frequency, resulting in partial cancellation
and reinforcement over the gamut of frequencies being reproduced. The end result can have a disastrous
effect on the quality of the reproduced sound. This also means the stereo transmission is no longer
compatible with monophonic reproduction when such errors exist.
2.
Precise adjustment. Precise azimuth adjusting is required for reel-to-reel and stereo tape
recorders. Earlier cartridge stereo systems did not provide for a tape-guide height adjustment, and the
arrangement of the tape path allowed considerable "creeping" up the guide posts. More recent tape
cartridges provide adjustable guide height as well as head adjustment. Some even have an additional
guide post installed prior to the original input guide for the tape entering its final path across the head for
a more rigid and flutter free state with just standard tension.
3.
Aligning stereo head. Using a fulltrack monophonic alignment tape is a good way to align a
stereo head. This allows excellent alignment of the two-head stereo assembly which receives equal
amplitude and identical phase from the two tracks at the reference frequency on tape.
Learning Event 5:
DESCRIBE AND IDENTIFY THE ELECTRONIC REQUIREMENTS OF RADIO RECEIVERS
1.
Radio receivers. The Federal Communications Commission (FCC) has assigned all radio
broadcast stations their operating frequencies. The amplitude modulated band (AM) is assigned 540KH
to 1.6MH, and the frequency modulated band (FM) is assigned 88MH to 108MH.
2.
Electronic requirements. Radio receivers must meet particular electronic requirements. Among
these requirement are sensitivity, selectivity, and fidelity.
a. Sensitivity means how well the receiver picks up or receives the broadcast signal. The higher
the sensitivity of the receiver, the better it will pick up (weak) broadcast signals.
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