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From: Kim =?iso-8859-1?Q?Fallstr=F6m?=
X-Mailer: Mozilla 4.78 [en] (WinNT; U)
Subject: Re: Problems with Creating a RF Tranformer
Date: Sat, 07 Dec 2002 00:51:20 +0200
NNTP-Posting-Date: Sat, 07 Dec 2002 00:51:20 EET
Organization: Jippii Customer
> Since a couple of weeks I try to build a RF Transformer but ...
> No Success...... :-(
> I've a Generator which produces a sine-wave : f = 2 MHz
> U = 5 Vpp
> Zout = 50 Ohms.
> The Transformer should convert the Inputvoltage to 300Vpp.
Output voltage is 1.76 Vrms and output power 0.0625 W
You want to get 106 Vrms (300 Vpp) voltage using 0.0625 W of power.
P = U*U/R => R = U*U/P = 180 kohm.
What kind of load are you connecting to your RF amplifier output?
If the load has a parallel resistance less than 180 kohms no
matching circuit can do the trick (of generating extra power).
If the load (and the maching inductance together) has a
parallel capacitance more than 26 pF the L circuit will
The impedance level of 180 kohms is probably impractical.
You are trying to do a 1:3600 impedance transformation
using a device (broadband rf transformer) which works best
at impedance transformation ratios less than 1:40.
For higher ratios you need tuned impedance matching circuits.
A tapped parallel resonance circuit or a "L" maching circuit
could work in theory. Some example of this kind of circuits
can be found on page
The simple L circuit will work if you can get an inductor
with L= 238 uH, a Q value of much higher than 60 (at 2 MHz)
and a self resonance frequency much higher than 2 MHz.
Above the self resonance frequency the coil looks
like a capacitance.
My advice is to use an external amplifier to push the power
level up to a few watts. Even at 1 W power the impedance
transformation level would be 1:225 (R = 11.2 kohm).
This is more practical as the impedance matching inductor
is now "only" 60 uH and the required Q value is down by
a factor of 4.
Look into the "ARRL Handbook for radio amateurs" for some
basic info on impedance matching.
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