Diagram of mounted radio antenna installation

1. Is the effect of placing an external antenna in the trunk of the car station worse than that in the middle of the roof?
A: There are four main indicators of the vehicle's antenna: maximum withstand power, center frequency, bandwidth, and standing wave ratio.
The first indicator is generally not taken into consideration, because generally, the maximum withstand power of the external antenna of the vehicle is more than, which is far greater than the maximum transmit power of the vehicle.
The last three indicators are correlated.
We know that there is a work scope for the vehicle platform. We often say that this is the 400 m low section (420-450) High Section (470-430) amateur section (440. Beyond this range, the receiving and receiving indicators of the Vehicle Platform (mainly including the reception sensitivity and transmission power) will drop sharply or even fail to work. The same is true for antennas. We call the perfect resonance frequency of the antenna as its center frequency. At this time, the standing wave ratio is 1, that is, all the power emitted by the vehicle is converted into electromagnetic wave radiation by the antenna. If we leave the center frequency standing wave ratio, it will gradually increase. When we increase the standing wave ratio to 1.5 (at this time, the reflection power is 5%), the band width is called the working bandwidth of the antenna. It is not recommended to work when the value of the standing wave is greater than 1.5. If the value of the standing wave is greater than 2, it cannot work. If the value of the standing wave is greater than 2.5, it cannot work. Otherwise, the car will be finished (of course, the car also has a protection circuit,, security cannot be absolutely guaranteed ).
Is there a high-power transmission (25 W) used in the vehicle to cause serious radiation to the human body?
The center frequency of the antenna is determined at the time of preparation. Generally, it is clearly marked on the packaging or nameplate. If it is not marked, it can also be measured using a traveling table. The bandwidth of an antenna depends on the following factors: Antenna form, material, quality factor, and gain. The first three factors will not be discussed here. Remember that the antenna with higher gain has a narrower bandwidth. Why? Isn't it clear that I want to run my horse again? If I want my horse to eat grass, it's impossible to Di. I can only drop one of the two ends.
The antenna is delivered to you, and the center frequency and increase benefit are fixed (generally, the nameplate of the antenna is marked with these two indicators). Then, according to the antenna form (rod? Miao Zi? Ribs ?), Material, production process can estimate the use frequency of the antenna. Experience data is: dB gain of stainless steel seedlings, its bandwidth is about 5-6 MHz.
OK. Three indicators are identified. The only indicator we need to pay attention to is the standing wave ratio.
Some people have to ask: No, it's strange that the antennas are all there. Isn't the standing wave still uncertain?
That's right! Standing Wave is related to the antenna installation location !!!
The on-board antenna needs to use the metal sheet on the roof (steel plate, don't worry about it. You opened a skylight ?? Case, handled separately !!) Build a local network to form an antenna system. Although the suction cup is insulated from a sheet metal, there is a small capacitor between the two, which is accessible at a high frequency. Changing the position of the antenna actually changes the local network of the antenna system, and the standing wave ratio will change.
Theoretically, the antenna should be placed in the middle of the roof. The ground network around this area is the best and the default position for the antenna factory test. However, in real life, Miao Zi may affect the local database too long, so some friends put the suction cup on the trunk or use the side. Is the antenna still working properly at this time?
My answer is: Not necessarily.
Don't worry. I'm not kidding you either. It's not necessarily true.
In other words, you may be more comfortable:
In theory, the on-board antenna should be placed in the center of the roof, but in fact, if properly adjusted, it can be placed in the trunk or placed anywhere using the side of the card, or even on the engine cover.
How about it? It's more comfortable. Alas, this is not because smoking is not allowed when reading the Bible, but can I read the Bible when smoking...
How to "adjust properly "? This time there is only one answer: using a standing wave table, measure the Standing Wave Ratio of the antenna at the selected position. Adjust the side of the measurement until the standing wave ratio is OK. OK means less than or equal to 1.5.
It is recommended that a club friend make up money to buy a good standing wave table. At present, the Japanese devil's brand new pass-through Standing Wave Power Meter is-MHz, which is-yuan. It's okay to have 50 members each.
Standing Wave Power Meter is far more useful than this. I used to measure the working status of an antenna system for a vehicle leg and found that the output power of the vehicle station was only 3-5 W and unstable. Remove the car platform with a false load measurement there is 30 W, carefully check, the original antenna feeder plug is not doing well, the screen has a few copper wires and core line short circuit.
-- This dude has been using this for half a year !! Thanks to moji's car platform, it would have been finished.
The second problem: Is there any serious radiation to the human body when the vehicle uses the maximum power to transmit (25 W) in the car?
Answer:
First, it is also the problem of standing wave. The standing wave ratio can be intuitively understood as the ratio of forward power to reflected power. When SWR is set to 1, all the power emitted by the vehicle station is sent out by the antenna system without reflecting power. If the antenna is open, that is to say, if all the power signals are not sent out and all the reflection is sent back to the vehicle platform, the platform is in danger.
There are three scenarios where the vehicle platform uses the highest power to transmit data in the vehicle:
1. no-load launch, without any antennas. As mentioned above, when all the power signals are not sent out, all the reflection is sent back to the vehicle. At this time, people will be fine, but the car station... Hey hey...
2. Launch with standard false loads. At this time, SWR = 1, all the electric wave energy is converted into thermal energy by the false load. At this time, the audience is OK;
3. Take Miao Zi to the car for launch. (Do you want to get full support? I still cannot get through it, # ￥ % ^ % ￥ #)
Miao Zi got the car and the antenna system was damaged (no land Network !), At this time, the standing wave ratio will be very high. That is to say, most of the power is reflected back to the vehicle platform, and little power is emitted. At this time, the car is definitely not comfortable, people are not comfortable, because you are not sure about how much radiation.
We can set up an extreme situation: Assuming the ideal antenna is used, all the electric waves are emitted in the car without being reflected back to the car. At this time, hahaha, hahaha, isn't the compartment a microwave oven? Do you want to make a roast suckling pig ??
Even in this case, the dangers of electric waves are not fatal or certainly do harm to health. There are two reasons.
First, the power is too small, 30 W, and the microwave oven is-w.
Second, the most important thing is that the frequency Mhz Radio waves are not microwave waves, which cannot cause resonance of molecules in your body to generate heat.
However, high-intensity radio waves can damage the body's immune system. The proportion of white blood cells is unknown.
Conclusion: All Forms of radio waves should be avoided in the vehicle as much as possible, including using a hand-mounted device, making a mobile phone call, and using a onboard Ozone Air Cleaning Machine ......