Message-ID: <000501c44291$64675040$2102000a@ibm>
From: "Dick" <knaap159@zonnet.nl>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 25 May 2004 21:00:09 +0200
MIME-Version: 1.0
Subject: LF: G0MRF-TX-ouput circuit troubles
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hello all,

Last weeks I spend a lot of time rewindg transformers,
changing the circuit time after time, and even changing the FET's.

All in all I have little progess sofar..............

Maybe there is an error in the schematic, from which I do not know.

The output transformer and some of the surrounding components seem
to play a key role in the results obtained.

I tried the tip Jim, M0BMU gave, with 2x4t bifilair (made of 3x4x0.3mm wire)
as primaire coil, and 16 turns secundair.
This coil didn't gave the results I expected.
I found an primairy inductance of 150uH , between the two outher wires and
37uH between the centre tap and each outher wire.
The secundairry inductance around 600uH.

The best results I obtained with an 36mm green 3E1 core.
Primairy 2 times 8 turns bifilair, inductance 900uH
Secundairy wound on top of it 15 turns, inductance 814uH.
(I don't think this core can withstand 400Watt...... Ui=4000 about
 twice as much as from a 3C90 core)

It seems that an almost 1:1 transformer gives the best results.

When measuring/compairing both transformers with an impedance bridge/noise
source
I found in both cases a strong 50Ohm dip in the 8-11MHz region, however
the M0BMU transformer wound on an ex-monitor core gave also another
dip of about 500Ohm around 1400kHz.

I am testing with a variable supply voltage to the FET's, and I think for
50V/10A
I should find somewhere around 4A at 20V.........

Maybe somebody has something to say about this......

73 Dick, pa4vhf