On 4 Feb 2005 21:04:19 -0800, "Jason" wrote:

Dear Bob,

I understand what you mean. But in the RF lecture, gain is given in db
unit, while IP3 is in dbm unit, then in order to find overall IP3 for a
cascaded system, the gain and IP3 which in different db unit are add or
deduct from one another without effort to change the unit. WHy is it
so?
Anyone can help?
By the way, how can I get notification from this newsgroup whenever
there is new contribution? No email notify me on this. How to do the
correct setting?


Assume that your system has IP3 = X dBm measured at point Y in the
system.

Assume further that there are amplifier stages A and B following point
Y, and that those amplifiers contribute a gain of A dB and B dB.

At the output of B the power level, in dBm, will be X + A + B.

In this way you avoid the confusion by clearly stating that the power
level at the output is X + A + B. In that context, the values can be
added, because you have made it clear that it is a power level in dBm
- not a gain in dB.

Regarding the auto-notification. I do not know of any such system.
Perhaps that is an opportunity for someone to develop a valuable
product.


Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html