The dBm unit is used to express several parameters of amateur radio equipment (decibelmiliwatt). Level 0 dBm corresponds 1 mW, or a voltage of 0.225V on the load 50 ohm. What is the meaning of it? We will show this in the following examples:
1, Increase of signal strength at the opposite station by 1S
One degree S corresponds to six decibels. Let's take an example: we have a 10W TCVR, which we feed into the dipole antenna with gain 0 dB. If we want, so that our signal at the opposite station is strengthened by exactly one S, we can either use an antenna with gain 6 dB, or increase the power of the transmitter by 6 dB. Ten watts is +40 dBm, we find out from the table, that +46 dBm is 40W. (Note that using a different type of antenna actually makes a bigger difference, because other factors also come into play)
2, How much will the sensitivity of the receiver increase by turning on the preamplifier with gain 10 dB?
We'll show it again with an example: our tranceiver has a specified sensitivity 0,25 uV for N/W ratio 10 dB at bandwidth 2,4 kHz. To what value will the sensitivity of the receiver be increased by turning on the preamplifier with gain 10 dB? We can find out by looking at the table, that tension 0,25 uV corresponds to the level -119 dBm. Level -129 It's dBm 0,08 uV na 50 ohmic load.
3, At what power level do harmonic products appear at the output of the transmitter?
Let's take a standard 100W tranceiver. We will read in the manual, that the suppression of harmonic products from the transmitter is 50 dB. But what is their performance at the output of the transmitter? According to the table, it is one hundred watts +50 dBm. If from +50 We subtract dBm 50 dB, we will get 0 dBm, that is 1mW.
4, What voltage does the diode mixer UZ07 need from the oscillator?
The UZ07 belongs to the category of mixers requiring an oscillator signal level +7 dBm. The small power meter does not appear in hamshack, but the VF millivoltmeter is relatively common. So that we set the right level for the mixer, we will change +7 dBm according to the table on 500 mV/50 ohm. We set the oscillator signal on the load to this voltage (on 50 ohm load, or directly on the outlet of the mixer).