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R: Impedance transformation




----- Original Message -----
From: Matt Davis <mattdavis21@hotmail.com>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, January 31, 2002 2:37 AM
Subject: [amsat-bb] Impedance transformation


>
> Hi,
>
> Please can soemeone advise me if I am doing the correct thing.
> I am interested to match a 50ohm connector to  10M ohm connector at vlf
e.g.
> 1 - 2 MHz.  While I am familiar with higher frequency matching using
quarter
> wave transformer, can I still use the same technique and replace the
quarter
> wave line with a resistor in parallel to the two connector having
resistance
> of sqrt(50*10e6)ohms.
>
> Thanks.
>
> Matt
>
>
Hi Matt,

You cannot use a resistor of  22360 ohm for matching because a resistor
is a dissipative device.

If you want to match a source impedance of 50+j0 ohm to such very high load
impedance 10e6+j0 ohm the best  matching can be obtained using a T section
matching  network.

                                    jXA                      jXC
          °----------|  |---------°---------|  |--------------°
                                         |
                                         \
IN=50+j0 ohm                 /  jXB                   OUT=9999 +j0 ohm
                                         \
                                          |
          °-----------------------|--------------------------
                                       /////

To compute the T matching network i have used the program
APPCAD from HP but the maximum real part allowed for the real
part of  the impedance is 9999 ohm

In any case i  have used 1,5 MHz as an average between 1 to 2 MHz
with the following results.

jXA= -705 ohm or 150,5 pF (picofarad) at 1,5 MHz

jXB=   709 ohm or 75 uH ( microhenries ) at 1,5 MHz

JXC=  -10   ohm or 10,6 nF ( nanofarad ) at 1,5 MHz

You can use the ARRL Handbook to build the 75 uH inductance

I hope it works  !

73 de i8CVS Domenico



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