[SOLVED] dB of a TV installation. power or voltage amplifier?

[ffddoo]

I am not sure if I am confused. I'm studying DVB antenna installations and I find that common units are dBuV (microVolts), which is voltage unit, but some places it seem to be used as a power unit, and i'm not sure if te amplifier gain, wich is in dB is voltage gain or power gain.

if Vi to an amplifier is for instance 40dBuV and the amplifier has a power gain of 16dB it is a voltage gain of 32dB, right? so Vo=40dBuV+32dBuv=74dBuV, right?

regards

 

[BigBoss]

dBuV is a Voltage Unit referenced to 1uV.
Power Gain is defined as Output Power/Input Power so reference impedance should be mentioned.( For TV application the reference impedance is always 75 Ohm )
If the Power Gain is 16 dB, you should convert this Voltage Level to dBm over 75 Ohm reference impedance. ( 40dBuV=-68.75dBm)
Finally your Output Power=-68.75+16=-52.75dBm=56dBuV=40dBuV+16dB
It's clear..

 

[ffddoo]

dBuV is a Voltage Unit referenced to 1uV.
Power Gain is defined as Output Power/Input Power so reference impedance should be mentioned.( For TV application the reference impedance is always 75 Ohm )
If the Power Gain is 16 dB, you should convert this Voltage Level to dBm over 75 Ohm reference impedance. ( 40dBuV=-68.75dBm)
Finally your Output Power=-68.75+16=-52.75dBm=56dBuV=40dBuV+16dB
It's clear..

So it's power gain and also voltage gain. Seems a newbie error but i have been confused because with linear Gain (same Z) G=Vo/Vi, then Po/Pi=G^2
But then in dB 20log(Vo/Vi) = 20log(G) = 10log(G²)= 10log(Po/Pi) right?

regards

 

[tony_lth]

from your equation, G_Power_dB=2*G_Voltage_dB

 

[keith1200rs]

So it's power gain and also voltage gain. Seems a newbie error but i have been confused because with linear Gain (same Z) G=Vo/Vi, then Po/Pi=G^2
But then in dB 20log(Vo/Vi) = 20log(G) = 10log(G²)= 10log(Po/Pi) right?

regards

This is correct. If you use power or voltage to work out the gain you should always get the same answer in dB. 100x the power is 20dB. 10x the voltage is 20dB. They are the same thing.

Keith