首先， dB 是一个纯计数单位：对于功率，dB = 10*lg(A/B）。对于电压或电流，dB = 20*lg(A/B)。dB的意义其实再简单不过了，就是把一个很大（后面跟一长串0的）或者很小（前面有一长串0的）的数比较简短地表示出来。如：

X=1000000000000000 （共15个0)

可以表示为：10lgX=150dB

X=0.000000000000001

可以表示为：10lgX=-150 dB

dBm 定义的是 miliwatt(毫瓦特)。0 dBm=1mw；

dBw 定义 watt。0 dBW = 10lg1 W = 10lg1000 mw = 30 dBm。

dB在缺省情况下总是定义功率单位，以 10lg 为计。当然某些情况下可以用信号强度（Amplitude）来描述功和功率，这时候就用 20lg 为计。不管是控制领域还是信号处理领域都是这样。比如有时候大家可以看到 dBmV 的表达。
HP350
First， an overview:
HP350 is a RF power meter， the instrument through the keys to complete the operation， advantages: simple structure， easy to use， stable and reliable performance， high sensitivity and fast measurement.
Two， application:
The RF power measurement;
- meter calibration;
Three， technical parameter table:
Item parameter unit remarks
1 measurement power range -80 ~ +10 dBm (external RF attenuator can be extended to 100dBm)
2 measurement power resolution 0.1 dBm
3 measurement frequency range from 0 to 500 MHz
4 measuring power 1nW ~ 2W
5 working voltage 7 ~ 12 VDC
6 working current mA <50
7 working temperature -40 degrees Celsius to 65 degrees Celsius
8 storage temperature -40 DEG C ~ 65 C Celsius
9 size 55*45*10 mm long X wide X high
Four， interface display and operating instructions:
(1) unit description: dBm;
(2) key note:
FUN: function keys; MODE: set interface; SEL: from the add or minus key;
4.1， display measurement data
Interface display font:
The first line "RF-POW -80.3 dBm"
Second line "0nW 20uV"
Note: display signal dBm value， input voltage value， input power.
4.2， set RF power attenuation value
Interface display font:
The first line "Attenuator RF"
Second line "000dB SUB"
Button operation:
FUN: function keys; (select the direction of addition and subtraction) show SUB is reduced， showing ADD as plus. (press the FUN key to save the set dB value)
SEL: self plus or minus key;
Note: different RF power attenuator， set the corresponding attenuation coefficient to read the correct power parameters.
Five， wiring
P1 connection definition:
Symbolic meaning of serial number
1 VDD module power positive (7V~12V)
2 GND module power cathode
P2 connection definition:
Symbolic meaning of serial number
1 FX not used
2 RF RF signal input
3 GND power cathode
Annotation:
First， dB is a pure count unit: for power， dB = 10*lg (A/B). For voltage or current， dB = 20*lg (A/B). The meaning of dB is actually simple， that is， a large (followed by a long string of 0) or very small (in front of a long string of 0) of the number of relatively short expression. Such as:
X=1000000000000000 (a total of 15 0)
Can be expressed as: 10lgX=150dB
X=0.000000000000001
Can be expressed as: 10lgX=-150 dB
DBm is defined as miliwatt (Vat). 0 dBm=1mw;
DBw definition watt. 0 dBW = 10lg1 W = Mw = 10lg1000 = 30 dBm.
DB always defines power units by default， with 10lg as the. Of course， in some cases， the signal strength (Amplitude) can be used to describe the power and power， this time with 20lg as the. This is true in both control and signal processing. For example， sometimes we can see the expression of dBmV.