# Can someone help me with this please

Discussion in 'Electronics Resources' started by zero_coke, Jan 30, 2013.

1. ### zero_coke Thread Starter Active Member

Apr 22, 2009
294
1

This power amplifier requires only a +30V signal at 5A, however, what I get on the output will also be a 0 to +30V signal? So technically, this is not an AC signal that is like -15 to +15 V but 0 - 30 V ??

2. ### w2aew Member

Jan 3, 2012
219
64
According to the data sheet, the amp will produce 60w of RF power, which is about 55Vrms. The fact that this amp is powered from a 30V DC supply really has no bearing on the RF output.

3. ### zero_coke Thread Starter Active Member

Apr 22, 2009
294
1
Ok so I can assume my output will be a AC sinusoid and not an AC sinusoid that is offset in the >0 V region where it would then just be a DC signal with a big ripple right?

Apr 5, 2008
15,530
2,300
Hello,

Did you ever look at the construction of RF amplifiers?
At work we use RF power amplifiers that use 28 Volts DC and give out 300 Vpp RF signal.
This is done with the use of RF transformers.

Bertus

• ###### RF_Power_Amplifiers.pdf
File size:
595.4 KB
Views:
24
Last edited: Jan 31, 2013
5. ### zero_coke Thread Starter Active Member

Apr 22, 2009
294
1
So Bertus, does a unipolar DC source applied to such power amplifiers provide a - to + sine wave at the output ? I don't understand , I took a look at the pdf but I didn't find it.

6. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
Actually it does. The one thing we know for certain sure is that the power output will always be less than the power input. To get 60 watts of RF power out of a 30VDC supply will require at least 2 Amperes assuming 100% efficiency. If we assume say 80% efficiency then 60 watts output will require 75 watts input or 2.5 Amperes @ 30VDC.

You are correct in stating that the number 30VDC all by itself is essentially meaningless except as it relates to the required current to provide the requisite input power.

7. ### zero_coke Thread Starter Active Member

Apr 22, 2009
294
1
Ok so here's my situation:

I have a weak AC signal @ 10 MHz passing through this amplifier. This amplifier wants +30V @ 10 A to deliver 140W at the output. That's all the specs I get for it. Now, my confusion is, my weak signal is an AC signal meaning it goes below and beyond 0V obviously. My question is, at the output end, since the DC supply is only +30 and not +/-30V, does this mean I will be getting an AC-like waveform at the output that only exists above the 0V plane?

I just don't see how only +30V DC can amplify my small signal's +5 and -5V peaks to +30 and -30V when the supply is only +30V. In the power amplifiers that we designed in class, they always had a + and - DC supply but these amplifiers that im looking at which are off-the-shelf only specify to use +30V only.

8. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
zero_coke likes this.

Apr 22, 2009
294
1
10. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
Google and Wikipedia are good friends who should be visited often. Some people think "lmgtfy" is a snide suggestion, but I'm amazed at how many people it has helped. Glad that you are a satisfied customer.

11. ### zero_coke Thread Starter Active Member

Apr 22, 2009
294
1
Yeah the problem in my case is I didn't know what to google or I would've done it prior to submitting a thread. Sigh, a simple capacitor solved my problems! I had no idea lol...Oh well, need to think clearly next time!

Thanks again!