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By DANIEL R. VON RECKLINGHAUSEN

Chairman, IHFM Sub-Commiłłee on Tuners Chief Research Engineer, H. H. Scott, Inc.

Solienł features of the Hi-Fi lnsłiłi?łe's recently adopłed słandards for measuring AM/FM łuners.

THE Institutc of High Fidclity Manu-facturers has recently released its first standard, IHFM-T-100, entitled “Methods of Measurement for Tuners.” This standard represents a step forward in the techniąues of tuner measurement. Previously. the only standards covering this field were those released by the Institute of Radio Engineers in 1947-48. These IRE standards were the best that could be de-vised at the time but later experience showed that certain necessary charac-teristics of tuner performance had not been included while other character-istics were measured in such a way that “good" test results did not neces-sarily mean “good” listening performance.

According to this new standard, a number of characteristics of either or both AM and FM tuners are to be measured: tuning rangę and frequency calibration, usable sensitivity. \olume scnsitivity, capture ratio, selectivity, amplitudę modulation suppression. fre-quency response, distortion, spurious response, hum and noise, frequency drift, radiation, automatic frequency control. squelch control, loop antenna, and crosstalk.

Standard Conditions

Ali of these listed characteristics are to be measured under “standard" conditions. These conditions are:

Carrier freąuencies: For FM tests, 90. 98. and 106 mc. and for AM tests 600, 1000, and 1400 kc. are standard test frequencies. Sonie tests are to be madę using only one carrier frequency in which case it will be 98 mc. for FM

and 1000 kilocycles for an AM tuner.

Since the settings of the various tuner Controls will affect test results. certain standardized control positions have been specified. For example, the a.f.c. control, if present, is set for minimum control; the sąuelch control for maximum sensitivity: any tonę Controls for flattest response as indicated by panel markings; and volume control for maximum. Only in the case of tuners which incorporate extra stages of amplification. such as units eąuipped with phono-preamplifier or power-out-put stages, should the volume control be set for 20 db attenuation. This is to prevent clipping of the audio signal due to excessive amplification.

Input voltages. their measurement, and dummy antennas to be used for both AM and FM testing have been specified. These standards are dia-grammcd in Figs. 1 through 4.

The standard test modulation has also been specified. For most tests. the modulation frequency. except for some distortion and frequency response tests, is 400 cps. The standard modulation for FM is 100^r/< or 75 kc. deviation while for AM this figurę is 30%, except for distortion tests. where 90% is to be used.

Usable Sensifivify

If one wished to specify the most important characteristic of an FM tuner, a measurement of “usable sensi-tivity“ would have to be madę. The definition and measurement of usable sensitivity constitute the most important contribution madę in the new standard. This term will be used gen-erally within a few months to describe the sensitivity of tuners rather than the “quieting“ figurę as defined in the IRE standards and used up to now. The best definition and test method covering usable sensitivity of FM tuners is found in Section 6.03.02 of the new standard. Here is this section in its entirety:

^uThis test is performer! at each of the standard test freguencies with the signal generator connected to the tuner under test through the standard 300-ohm dummy antenna. The signal generator should be freąuency modulat-ed with standard test modulation. The Controls of the tuner słlall be set to the normal control settings. The signal intensity should then be reduced to the least value which will produce a 30 decibel rise in indicated output with standard test modulation as ctnnpared with the indicated output with standard test modulation measured through a ifOO-cps nuli filter. This test serves to indicate the relatire freedom of the tuner from objectionable internat re-ceirer noise during pauses in modulation and receiver noise is least likely to be masked by motlulation. This test also ser ces to indicate the relatice freedom of the tuner from objectionable distortion during periods of muxi-mum modulation.

“The results are expressed in micro-volts.”

What is new^f and different about this definition and how does it help the user to decide about the performance of a tuner?

First, this and all other measure-ments in the new standard are to be

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