>Maybe what has confused you is the power sum of two tones is
>NOT twice the original tone.
>
>For example in a two tone test the sum of the two equal tones is
>six dB greater than a single tone, not 3 dB. That's why, if you look
>at the ARRL IMD settings, they set the individual tones six dB
>below the reference PEP to read IMD below PEP. PEP is not RSS,
>or RMS.
Huh?
Help me understand something here, Tom.
Say I have a single tone at 5 dBm going into my amplifier. If I want to
use two tones that give me the same composite input power, I use two
tones that are each at half the power of 5 dBm. When working in dB's
decreasing by 3 dB gives us half power. So half the power of 5 dBm is 2
dBm.
So two tones at 2 dBm each make a total composite power of 5 dBm.
If you calculate it by using milliwatts instead, 5 dBm is 3.16 mW.
3.16/2 = 1.58
2 dBm is 1.58 mW!!! Gee, it works.
I don't know how you can make the claim that two equal tones combine to
make a 6 dB increase in power. That would say that if I put two tones of
2 dBm in, than the composite is 8 dBm! That isn't correct. That would be
saying you get more out than you put in.
Look at it this way: I have a carrier at a single frequency of 5 dBm. I
split that with a 3 dB splitter. Assuming no loss I now have two singals
in two branches of 2 dBm each. Now I recombine those two signals.
Assuming a lossless combiner, we now are back to 5 dBm. I know that in
this example the tones being combined are at the same frequency, but I
still think it holds.
How do you get out more than you put in?
And I know from my measurement days that when I measured two tones each
at half the power of my single tone that I did NOT measure 6 dB higher.
I measured very close to my original single tone value. It was with
tenths of a dB.
I can tell you that a lot of lab grade power meters are really designed
for CW signals and not modulated signals. The modulation screws them up.
So perhaps in your world, these are trash and the solution can be done
cheaply and easily.
Please explain how two tones of 2 dBm each make a total of 8 dBm and not
5 dBm.
73,
Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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