On 9 Sep 2006 11:23:33 -0700, "Professor"
wrote:


K7ITM wrote:
Hi all,

Every once in a while I come across an anomaly in RFSim99. I'd be
happy if someone could tell me that I'm doing something wrong in the
following:

Fire up the simulator. Tools--Design--Attenuator. Pi Section, 50R
input impedance, 50R output impedance, 10dB attenuation. Simulate.
!Current schematic will be overwritten; OK. Now note that the graphics
window displays S11 as 2E+31dB.

In the circuit window, edit the values of the two 96.25 ohm resistors;
they have apparently been simulated to more decimal places than shown.
Just manually enter 96.25 ohms for each. Now the magnitude of S11 and
S22 show up as -102.69dB; that seems reasonable. The phases for S11,
S12, S21 and S22 are all zero. Now, from the graphics window,
---snip---

Aarrgg! This is very disappointing! I usually check at least my
values for LC circuits against the LADPAC programs In "Experimental
Methods in RF Design", however. By the way, when I click on
Tools/DesignAttenuator, the schematic that is in the pop-up window for
default 10 dB shows the three resistor values as 71.151 and 96.248.
When I go through the process you did, I get the same results. I
saved the file, and closed and reopened the program. Then, I loaded
the saved 10dBAtten.cct file, and of course got the same -102.69 dB
for S11. Then, I Tuned the values back to 71.151 (which immediately
displayed only 71.15), and tuned the other two to 96.248, (which
displayed 96.25). When I simulated, S11 was now -107 dB!

Regards,
Ted KX4OM