Radio product inspection and testing certification standards (FM/AM performance testing)
During the inspection, factory verification and certification process of radio products, the following key performance indicators need to be strictly tested. The inspectors should operate according to the standard procedures to ensure the accuracy and traceability of the data.
1. Practical Sensitivity (30dB S/N)
Test purpose: To evaluate the minimum input level of the receiver at a signal-to-noise ratio of 30dB.
Inspection procedures:
Set the tested machine to 90 MHz (or 98 MHz, 106 MHz), adjust the output level of the signal generator to the normal value, and set the volume to 0 dB.
Shutdown signal (ON/OFF), millivolt meter attenuation 30 dB (decrease by 3 steps, each step 10 dB).
Adjust the output level of the signal generator so that the pointer of the millivolt meter coincides when there is a signal and when there is no signal (the deviation should be ≤ 1 dB).
The level value displayed by the signal generator at this moment is precisely the 30 dB practical sensitivity.
II. 3% Distortion Sensitivity (Intermediate Frequency Sensitivity)
Test purpose: The minimum input level under the condition of 75kHz frequency deviation and total harmonic distortion of 3%.
Inspection procedures:
The machine was set to 90 MHz (98/106 MHz), with a frequency offset of 75 kHz, and the distortion meter was placed at the DIS 10% (-20 dB) setting.
Adjust the volume and the signal generator level so that the reading of the distortion meter fluctuates within 3% and the millivolt meter reads approximately 2V.
The level displayed by the signal generator at this moment is the 3% distortion sensitivity.
III. -3dB Limiting Sensitivity
Test purpose: The maximum input level when the output drops by 3dB.
Inspection procedures:
The machine is set to 98 MHz, the signal level is 66 dB, and the volume is adjusted to 0 dB.
Reduce the signal generator level until the millivolt meter reading drops by 3 dB. Stop when this occurs.
Record the current level value, which is the -3dB limit sensitivity.
IV. Signal-to-Noise Ratio (S/N Ratio @ 1mV Input)
Test purpose: Signal-to-noise ratio under a 1mV input signal.
Inspection procedures:
The machine is set to 98 MHz, with a level of 66 dB, a volume of 0 dB, and the signal is turned off.
The millivolt meter is decibels per decibel (repeated multiple times) reduced until the pointer does not exceed 0 dB.
The total attenuation in decibels plus the pointer indication value equals the signal-to-noise ratio (for example: 5 levels = 50 dB, pointer 9 → 59 dB).
V. Intermediate Frequency Suppression (I.F Rejection)
Test purpose: To verify the ability to suppress intermediate frequency interference.
Inspection procedures:
The practical sensitivity at 90 MHz was measured.
Change the frequency of the signal generator to 10.7 MHz (middle frequency), and adjust the level so that the millivolt meter reads 2 V.
Subtract the practical sensitivity from this level value, and the difference is the intermediate frequency suppression (in decibels).
VI. Intermediate Frequency
Inspection steps: When measuring the intermediate frequency suppression, adjust the frequency of the signal generator to make the waveform as accurate as possible. The displayed frequency at this time is the intermediate frequency (for example, 10.69 MHz).
VII. Image Rejection Ratio
Test purpose: To evaluate the ability to suppress the image frequency.
Inspection procedures:
The practical sensitivity of 106 MHz (typically 105.9 MHz) was measured.
The input mirror frequency of the signal generator: 105.9 MHz + 2 × 10.7 MHz = 127.3 MHz.
Adjust the level so that the millivolt meter reads 2V. The level value minus the practical sensitivity is the image rejection ratio. If it cannot be adjusted to 2V, record as >100dB.
Similarly for AM: Mirror frequency = Reception frequency + 2 × 455 kHz.
VIII. AM Limitation (AM Suppression)
Inspection steps:
The machine is set to 98 MHz, with a level of 66 dB, a volume of 0 dB, and a modulation rate of 30%.
For each 10 dB attenuation of the millivolt meter, the pointer should not exceed 0 dB. The total attenuation plus the pointer value represents the AM limiting value.
IX. AFC Control Range (AFC Holding Range)
Inspection Steps:
The machine is set to 98 MHz, with a level of 66 dB and a volume of 0 dB.
Press the ΔF key to adjust the frequency in the positive or negative direction until the millivolt meter drops by 3 dB. Record the adjustment amount.
X. Selectivity (Selectivity @ ±200kHz)
Inspection steps:
The measured practical sensitivity is 98 MHz and the volume is at its maximum.
Offset the frequencies by ±0.2 MHz respectively, and then increase the level to make the millivolt meter return to its original sensitivity reading.
The level value minus the practical sensitivity gives the selectivity (in dB).
XI. Frequency Response (Fidelity -3dB)
Test Purpose: Frequency response of the demodulated audio (pre-emphasis 50μs or 75μs).
Inspection procedures:
The machine is set to 98 MHz, the level is 66 dB, the signal generator is set to EXT (external modulation), and the decoding generator is set to 50 μs (European standard) or 75 μs (American standard).
Set the volume to 0 dB based on a 1 kHz reference.
Change the low-frequency setting, and measure the upper and lower limit frequencies when the output drops by 3 dB.
12. Standard output distortion (T.H.D @ 1mV input)
Inspection steps:
The machine is set to 98 MHz, the level is 66 dB, the distortion meter is in the DIST position, and the volume is adjusted to 2V.
Directly read the percentage of distortion.
Thirteen. Overload Distortion
Inspection steps:
The machine is set to 98 MHz, with a level of 66 dB, a frequency deviation of 75 kHz, and the volume adjusted to 2V.
Read the values of the distortion meter. In AM mode, the modulation is 80% and the level is 100 dB.
Fourteen. 10% Distortion Output Power (10% T.H.D Output Power)
Inspection steps:
The machine is set to 98 MHz, with a level of 66 dB and a modulation rate of 30% (FM) or the corresponding settings for AM.
Adjust the volume so that the reading of the distortion meter is 10%, and then read the voltage V of the millivolt meter.
Power = V² / R (where R is the load resistance, usually 4Ω).
15. Maximum Output Power
Inspection steps: Turn the volume to the maximum, set the modulation to 75 kHz (FM), read the voltage on the millivolt meter, and then calculate the power.
16. Automatic Stop Channel Sensitivity (Auto Seek Sensitivity)
Inspection procedure: At a 22.5 kHz frequency deviation, the lowest stop channel level measured is the automatic stop channel sensitivity.
17. Long and Short Range Effect (LO/DX Effect)
Inspection steps (for computer models): Measure the stop threshold sensitivity in both normal and LOC-activated states, and the difference is the LO/DX effect. For hand-adjustable models: Measure the practical sensitivity, then activate LOC, increase the level to make the millivolt meter return to 0 dB, and the difference is the LO/DX effect.
18. Stereo Separation (Separation @ 1mV Input)
Inspection steps:
The machine is set to 98 MHz, the level is 66 dB, the frequency deviation is 75 kHz, and the volume is adjusted to 0 dB on the right pointer of the millivolt meter.
Left channel test: The left pointer of the millivolt meter should decrease by 10 dB each time, but not exceed the right pointer.
The right channel is handled in the same way (switching between decoder channels).
19. Stereo Indicator Sensitivity (Stereo Indicator On Sensitivity)
Inspection steps: Set the machine to 98 MHz, set the level to 66 dB, set the frequency offset to 75 kHz. Reduce the level until the stereo indicator light just turns on. Record the level value.
Twenty. 20dB separation / 3dB separation (SNC Separation)
Inspection steps (20dB):
The machine is set to 98 MHz, with a level of 66 dB, a frequency deviation of 75 kHz, and the volume adjusted to 2V.
The millivolt meter is set to a 20 dB attenuation (reduced by 2 steps), adjust the level so that the two pointers align, and record the level.
3dB separation: Adjust the level so that the difference between the two pointers is 3dB, and then record the level.
Summary: The above testing items comprehensively cover the key performance indicators of radio products. During the inspection process, the inspectors should strictly follow the procedures, record the data and compare them with the standard values. During the factory inspection, it is necessary to verify whether the factory has the corresponding testing equipment and calibration records. The final products can obtain certification reports through third-party inspections to ensure compliance with market entry requirements.
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Radio product inspection and testing certification standards (FM/AM pe
Radio product inspection and testing certification standards (FM/AM performance testing)