"JGBOYLES" wrote in message
...
1500W into 50 Ohms yields 274V which you then divide by 27.4 to obtain
10V.
As you already have 10V by divider action, what do you need to
multiply?

Hi Richard, I want 10.00 VDC to indicate 1500 watts on my 0-10v meter
with a
linear scale. If I run the 10 volts thru the multiplier (squaring)
circuit I
get (10)**2/10=10 volts. So far so good, and you don't need a multiplier.
500W into 50 Ohms yields 158V which you then divide by 27.4 to obtain
5.77V. OK

If I run 5.77v to my 10 volt full scale meter it will read
5.77/10*1500=865.5
watts which is not 500 watts. However, if I run 5.77 thru my squaring
circuit
I get (5.77)**2/10=3.33 volts. Now my meter reads 3.33/10*1500=500 watts
which
is correct.
If you plot the voltage across a 50 ohm resistor vs power V**2/50=power,
you
get a squared relationship. You can use volts to represent watts only if
you
scale the meter face correctly. I have seen wattmeters that did this. I
believe the Drake model did. 0-100 watts took up the first half of the
meter,
and 100-1000 watts took up the other half.
If you linearize the voltage by squaring and scaling you get a nice
readout
with 100 watts being on the left hand side of the meter, and 1500 on the
right
hand side, and linear in between.
The AD633 probably uses log amps in realization of multiplication, I
haven't
looked at the internals. I have done multiplication with Log amps. I
have to
disagree on the AD538 being a better solution. One could use the 538, but
the
633 is much simplier to use. Also I already had some AD633s
73 Gary N4AST

Gary,
Comment I have is in your resistive divider. To keep the power dissipations
in the resistors low, you will have to use large resistor values, but at RF
these can be off 50 % or more. So, you will want to build what looks like a
'scope probe, with each of the resistors shunted with a capacitor, where the
two RC products are the same. For starters, try something like 2 - 5 PF for
the smaller capacitor. Do not use ceramic capacitors, except for NPO. I
would build the thing with at least 2 scales, say 0 - 150 and 0 - 1500 W.

Tam/WB2TT