[Elecraft] K2 s/n 3602 had it's first completed qso ...

Sat Oct 25 16:35:01 2003

Hi, Jan:

I'll tackle the RF Probe question.

You are right that the 4.7 megohm resistor provides RMS voltage readings =
if,
and only if you have a 11-megohm input impedance meter. Most (but =
clearly
not all) modern DMMs provide this -  as did  the popular "vacuum tube
voltmeters" popular before DMMs appearing on the scene.=20

You can get rid of the resistor, or you can figure out the correction =
factor
you need based on your meter's impedance. If you get rid of the resistor =
you
will, of course, be measuring the peak RF voltage, so you need to =
multiply
that value by 0.707 to get the RMS value needed to calculate power using
P=3DE^2 / R.

Dropping the resistor out will limit your measurements with most diodes =
to
about 5 watts. Above that you will exceed the Peak Reverse Voltage =
rating of
many diodes.

Ron AC7AC

-----Original Message-----
From: [email protected] =
[mailto:[email protected]]
On Behalf Of Jan Reidar Oeverland
Sent: Saturday, October 25, 2003 10:11 AM
To: [email protected]
Subject: [Elecraft] K2 s/n 3602 had it's first completed qso ...
...
The manual states that the RF-probe  should give a DC reading equal to
Vrms.   The probe  comes with  a 4.7M  series resistor,  that  gives a
reading  equal  of Vrms  only  if the  DVM  has  11M input  impedance.
However, my  DVM has 1M  input impedance.  The ratio  is (4.7+1)/1=3D5.7 =
which
is approximately four  times 1.414  and not  close to  Vrms.  I haven't =
seen
anything in the manual explaining this.  Unless I applied the wrong =
math, a
note about  scaling the series resistor to match the input impedance of =
the
DVM might be a good idea.
...

--=20
73                                       GnuPG KeyID:    0x8C0BFDA4=20
	Jan Reidar =D8verland LA7RKA       <http://www.keyserver.net>