We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
OUTPUT
_20| CORRECTED FOR F LOSSES
-30 -, CORRECTED FOR F a * LOSSES
Fig. 8. Short-gap surfac induction at the tw speeds.
O o
* * o in
Fig. 9. Theoretica long-gap output.
.5 I 2357
wavelength loss of the order of ±1 db was found at the extreme low-frequency end of the output curve. This could have been measured by using very low tape speeds. Actually, it is fair to assume in this region that the surface induction is proportional to recording current.
The long-gap method of measuring surface induction also consists of calibrating a reproduce system, but in this case a playback head is used that has an effective gap length which is long with respect to the wavelengths to be measured.
An ideal long-gap head connected open circuit and with constant induction has a voltage output with alternate maximum points and nulls. The output curve is assumed to follow the equation :
E = K sin ^ as shown hi Fig. 9.
The constant K includes the surfao induction, the gap length and the spew of the tape. From the equation
dE_
T
(I)
KIT COS —
A
The maxima occur when 8 = X, X
etc., or when 5
.(.-1),
The minima occur when 5 = nX. The value of E at the maxima equals i \ constant. Therefore the locus of max-i ima with an ideal head is a straight lint i and flat. This line represents surface j induction directly.
A nonideal head together with it! amplifier will have a locus of maxims i other than a straight and flat line. Thif i is due to frequency losses which can txi corrected and secondary wavelength i
522
April 1953 Journal of the SMPTE Vol.60