Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Tim Hite]

Having difficulty understanding the difference between gain and power output in an RF system.

Let's say I take a small amplifier like This one right here. . .:

I feed the amplifier from an IEM system. The amp is set to accept 15dBm max input so I feed it 25mW from the IEM antenna output and some 12VDC.

The amplifier spec shows a gain of 15dB and a nominal output power of ~21dBm.

I would expect from calculating power for 15dB gain @ 25mW to be 140mW. . .

but. . .

The amp spec also says the output power is 21dB or ~125mW total power.

How do I correctly calculate the output power of the system? What am I missing?

[Jason Glass]

Having difficulty understanding the difference between gain and power output in an RF system.

Let's say I take a small amplifier like This one right here. . .:

I feed the amplifier from an IEM system. The amp is set to accept 15dBm max input so I feed it 25mW from the IEM antenna output and some 12VDC.

The amplifier spec shows a gain of 15dB and a nominal output power of ~21dBm.

I would expect from calculating power for 15dB gain @ 25mW to be 140mW. . .

but. . .

The amp spec also says the output power is 21dB or ~125mW total power.

How do I correctly calculate the output power of the system? What am I missing?

That amplifier is capable of a maximum output (P1) of 21dbm, beyond which the signal compresses and distorts.  Its +15dBm maximum input spec refers to the point at which it begins to destroy itself.  In practical use, an amp with 15dB gain and 21dBm P1 will perform acceptably with an input level less than +6dBm.  21-15=6

Actually, most affordable RF amps will begin  to degrade the signal at lower levels than the specs imply and require a bit of extra headroom to remain linear.  In this case I would start at +0dBm input and measure the output on a spectrum analyzer as input power is increased to determine the point at which distortion and noise become intolerable for the application.

Sent from my mobile phone using Tapatalk

[ProSoundWeb Community]