What are the methods of cable TV amplifier detection and debugging?
When designing and debugging traditional cable TV user amplifiers, limited by the distribution value of user amplifier distortion indicators, they can only use a relatively large range of output level values and input level values. This design and debugging method is not conducive to improving the amplifier's performance. User allocation efficiency, it is difficult to guarantee its carrier-to-noise ratio index. Next, I will tell you how to detect and debug the cable TV amplifier, I hope it will be helpful to you!
1. First check whether the power supply system of the trunk amplifier is normal. If there is no problem, turn on the power supply (60V) to supply power to the amplifier.
(1) Connect the field strength meter to the input level test port of the trunk amplifier to measure the input level (image carrier frequency) of each channel. If the input level of the trunk amplifier is higher than the rated input level, insert a fixed Attenuator, its value is: actual input level - rated input level = inserted attenuator value.
In fact, the gain of the amplifying module in the amplifier is not adjustable. To change the amplifier gain (or level), you need to adjust the attenuator value to reduce the input level, thereby reducing the output level to achieve the purpose of adjusting the amplifier gain.
(2) Level adjustment of the AGC trunk amplifier: put the AGC switch of the amplifier in the manual mode, adjust the gain potentiometer to make the output level the design value (generally 98~102dBV), adjust the slope potentiometer to make the output signal tilt about 3dB, and then Set the AGC switch to automatic mode, adjust the potentiometer on the AGC control unit, and make the pilot signal output level the design value.
Check whether the output level and slope meet the requirements. If the requirements are not met, it can be adjusted repeatedly to reach the design value. The smaller the amplifier output level is, the better it meets the technical specifications.
(3) Distribution amplifier output level setting: Connect the field strength meter to the output level test port of the distribution amplifier, adjust the gain potentiometer (or insert an attenuator) to make the output level the design value (generally 105~108dBV), adjust The slope potentiometer makes its output slope around 4dB.
2. Amplifier maintenance
Amplifiers are important active devices. They are often installed in the field, exposed to the sun and rain, and work continuously around the clock. Faults often occur. Therefore, they should be checked every six months, mainly to check whether the power supply of the amplifier is normal, whether there is flashover or leakage. , Low voltage and other phenomena, whether the connectors and connectors are in good condition, whether the waterproof measures are in good condition, check whether the input and output levels are consistent with the recorded values of the amplifier level meter, and deal with them in time if any abnormalities are found.
3. User level detection and maintenance
(1) According to the national standard, the level value of each channel at the terminal output port should be (644) dBV, the difference between any channels is ≤10dB, and the level difference between adjacent channels is ≤2dB. Make adjustments, connect the field strength meter to the user terminal port, test whether the level meets the above requirements, and adjust the gain of the distribution amplifier and the corresponding passive components (distributor, splitter, equalizer, etc.) to meet the design requirements.
(2) The failure of every link in the network transmission will be reflected on the user's TV screen, so it is very important to quickly determine the location of the failure.
For example, if most users in a certain area report that there is a fault in the cable TV, there may be a problem with the corresponding trunk amplifier or user amplifier; or if only one building user reports a fault, then there may be a problem with the distribution amplifier or branch or distribution device of the building; if there is only one If the user reports that there is a fault, then there is a problem with the user terminal.
Common faults include: changing the circuit and components without permission; terminal boxes and plugs with poor crimping, problems such as broken cores, shrinking cores, and short circuits; problems with the user's TV.
