[ICOM] IC-7000 AM Modulation Problem

[D C *Mac* Macdonald]

To calculate dB for Voltage or Current

*                Va
*  dB = 20 log ------
*                Vb


          OR


*                Ia
*  dB = 20 log ------
*                Ib


To calculate dB for Power

*                Pa
*  dB = 10 log ------
*                Pb


The result  WILL  be the same for a given
circuit, assuming linear operation of that
circuit.

73 - Mac, K2GKK/5
Oklahoma City, OK



----Original Message Follows----
From: <w8okn at charter.net>
To: ICOM Reflector <icom at mailman.qth.net>
CC: D C *Mac* Macdonald <k2gkk at hotmail.com>
Subject: Re: [ICOM] IC-7000 AM Modulation Problem
Date: Fri, 7 Apr 2006 12:49:20 -0700

DB is simply a method of comparison based on logarithm
if I recall my EE math.

The logarithm of any given number is the exponent of a
power to which another given invariable number, called
the base, must be raised in order to produce that given
number. Thus, let 10 be the base, then 2 is the logarithm
of 100, because 10^{2} = 100, and 3 is the logarithm of
1,000, because 10^{3} = 1,000.

So, 10 to the 3rd is therefore 2x.  3db gain (or differential
perhaps might be easier to think about) is a comparison of
one value to another, in simple terms.   3 dbd would then be
2x over a dipole.



---- D C *Mac* Macdonald <k2gkk at hotmail.com> wrote:
  > dB   ARE   dB.  They are identical in absolute quantity.
  > The difference is that they are derived differently for
  > voltage, current and power.  The formulas for computing
  > dB are different, but the absolute difference in dB between
  > two signals will be the same if calculated with the correct
  > formula.
  >
  > Application of Ohms Law will show that doubling the
  > applied voltage will also double the current, resulting in
  > quadrupling of the power.  Figure dB change for any
  > of these three specific quantities with the correct
  > formula will give the same result.
  >
  >
  > Mac - K2GKK/5
  >
  >
  >
  > ----Original Message Follows----
  > From: C Whitaker <whitaker at pa.net>
  > Reply-To: ICOM Reflector <icom at mailman.qth.net>
  > To: ICOM Reflector <icom at mailman.qth.net>
  > Subject: Re: [ICOM] IC-7000 AM Modulation Problem
  > Date: Fri, 07 Apr 2006 14:20:06 -0400
  >
  > de WB2CPN
  >
  > I wonder if we get confused when we're calculating
  > dB when we don't consider whether it's Voltage dB
  > or Power dB, there being considerable difference in
  > the numbers.
  >
  > 73  Clete
  >
  >
  >
  >
  > ----
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  >
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