[Amps] Discrepancies in Pi-net calculators

[jim.thom jim.thom@telus.net]

I've been working through some Pi-network design for an input tuning

network recently and have tried out several online calculators as

well as traditional formulas and  common software.  Using the same

input variables for each tool, I generated three very different

 results.



For Rin = 50 ohms, Rout = 135 ohms, f=28.03 MHz, Q=2.7



Group 1:  Tonne's PI-EL software, ARRL Handbook formulas, and Jim

Hawkins online Java Radio Calculator.

Cin = 93pF, L=457nH, Cout=79pF



Group 2:  VK1OD online calculator, electronicdesign.com calculator,

and raltron.com calculator.

Cin = 307pF, L=251nH, Cout=194pF



Group 3:  EEweb.com calculator, VK2ZAY online calculator, and

Impedance Matching Network Designer online calculator (sandiego.edu).

Cin=163pF, L=383nH, Cout=113pF



So then, you can see my dilemma here.   Why are these so different?

And why the common groupings?



Steve, KK7UV

####  The above was from way back in Nov, 2013.

Using the  GM3SEK PI software, it's easily explained.   In Group 1, an  an

 OVERALL network Q of 2.7 is used.  IE: input Q of .8  and  an output

Q of  1.9   (.8  + 1.9  =  2.7)


In  Group 2,  an  INPUT Q  of  2.7 is used ! (and an output Q of  4.5)

Overall network Q = (2.7 + 4.5) =  7.2


In  Group 3,  an  OUTPUT Q of  2.7 was used. (input Q is 1.4)

Overall network Q = (1.4 + 2.7) =  4.1


In  EACH case, when the OVERALL network Q is inputted into the GM3SEK

PI  software, it spits out  IDENTICAL results, as  steve quoted.

for each of the 3 groups.

There is no real discrepancy per se.   The discrepancy lies in whether

one specifies  OVERALL network Q, OR INPUT Q... OR OUTPUT Q.


Myself, I use an overall network Q of 4. When using tubes with a

50 ohm input Z, both the input and output Q = 2.

Note GM3SEK's PI net software will not handle 2 identical Z's.

To fool the  software, the output / cathode /tube end is inputted

as 50.00001 ohms. Input Z is entered on Line 35.  Output Z is on

line 37. Enter 0  in all other fields  EXCEPT the plate choke.

Enter 9999 for the  plate choke.


Note his  group 2 has  way too high an overall Q for use as a

tuned input.  It would be extremely narrow banded.

Ok, the mystery is finally solved after just 9 years !


Later.... Jim  VE7RF