Performance characteristics
3.—(1) Frequency range
The measuring apparatus shall be suitable for use at any frequency in the range 40 Mc/s to 70 Mc/s. The receiver shall be capable of being set, to an accuracy of ± 1 per cent., to receive any desired frequency within its range.
(2) Field-strength sensitivity and accuracy
Values of field-strength, greater than 20 microvolts per metre at any frequency throughout the range of frequencies from 40 Mc/s to 70 Mc/s, shall be measurable to an accuracy of ±3 db.
(3) Attenuators
The calibrated attenuators shall be so constructed and disposed that no performance characteristic of the set, apart from gain, is significantly affected by variations in their settings.
(4) Overload characteristic
With the measuring apparatus adjusted to give reference deflection of the meter for an applied sinewave voltage of any value between 20 microvolts and 100 millivolts, the sinewave voltage measured at the input of the value-voltmeter shall be proportional to the applied voltage within ± 1 db up to a voltage 40 db above that producing reference deflection.
(5) Overall frequency characteristic
The variation with frequency of an applied sinewave voltage to produce a constant voltage at the input to the valve-voltmeter, when no alteration is made to the tuning of the apparatus, shall not exceed the limits of the marked area of Figure 1.
(6) Frequency characteristic of radio-frequency amplifier
The increase of an applied sinewave voltage needed to produce a constant voltage at the control grid of the frequency changer valve shall be not less than 6 db when the frequency of the applied voltage is varied from the tuned frequency by ±2.5 Mc/s.
(7) Spurious responses
The applied sinewave voltage of the tuned frequency which produces reference deflection of the meter shall be at least 80 db lower than the applied voltage at any other frequency which combines with a harmonic and not the fundamental frequency of the local oscillator to produce reference deflection.
(8) Image frequency response
The ratio of the applied sinewave voltages which produce reference deflection at the image frequency and at the tuned frequency respectively shall be at least 40 db.
(9) Intermediate frequency response
The ratio of the applied sinewave voltages which produce reference deflection at the intermediate frequency and at the tuned frequency respectively shall be at least 40 db.
(10) Screening
The overall screening of the measuring apparatus shall be such that when the measuring apparatus is in a field of a strength requiring a setting of 40 db for the R.F. attenuator and at least 30 db for the I.F. attenuator to produce reference deflection, the following requirements shall be met for all orientations of the measuring apparatus excluding the aerial:—
(a)The decrease in the setting of the I.F. attenuator required to increase the meter reading from reference deflection to full-scale deflection shall not exceed 6.5 db.
(b)The decrease in the setting of the I.F. attenuator required to return the meter to reference deflection when the setting of the R.F. attenuator is increased from 40 db to 60 db shall be at least 19 db.
The overall screening shall also be such that, with the receiver tuned to any frequency within its range and with the aerial disconnected and the gain of the receiver adjusted to that used for that frequency when the measuring apparatus was calibrated, the change in the I.F. attenuator setting required to return the meter to reference deflection when an external electromagnetic field of that frequency and of a strength of 86 db above 1 microvolt per metre is switched on shall not exceed 1 db. This requirement shall be met for all orientations of the measuring apparatus. For this test screening covers may be placed over the aerial input and voltage input terminals.