Envelope-to: dave@picks.force9.co.uk
Delivery-date: Wed, 28 Sep 2005 11:41:05 +0100
Message-ID: <B333AB0EF6D4D4118BAF00508BAED8EA088DA7A4@mms12014.stv.uk.astrium.corp>
From: "OSBORN, Chris" <Chris.OSBORN@astrium.eads.net>
To: "'rsgb_lf_group@blacksheep.org'" <rsgb_lf_group@blacksheep.org>
Date: Wed, 28 Sep 2005 11:40:20 +0100
MIME-Version: 1.0
Subject: LF: RE: Re: Advice will be gratefully received
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Content-transfer-encoding: 8bit


Thanks for the advice Jeff,
All points noted.

I must confess that all of the published designs seem to use a logic driver
IC.
I must be being awkward using an inductor :-(
Maybe I'd better stick to a proven design..

I'll take a photo soon and risk ridicule - HI!

73 Chris G3XIZ


-----Original Message-----
From: F6CWN [mailto:f6cwn@tiscali.fr]
Sent: 28 September 2005 10:21:AM
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: Advice will be gratefully received


Hello Chris,

At first,"RIP poor MOS"!

I prefer use MOS with higher VDS.
The driver must absorb energy, because the Ciss capacitance, i use TSC426 or
TC4429 driver.
It sis better to separate the cooling radiators to minimize the reaction
between the two parts
of the bridge (capacity Drain / Ground, the ground is "hot").
A problem with reactive loading, the coils of the LPF are reversible.
A little photography of your PA can help...

73: Jeff / F6CWN/p


----- Original Message ----- 
From: "OSBORN, Chris" <Chris.OSBORN@astrium.eads.net>
To: "LF Group (E-mail)" <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, September 28, 2005 10:43 AM
Subject: LF: Advice will be gratefully received


>
>
>
> The PA FET's in my new home brew transmitter keep exploding !
>
> I'm using push-pull  IRF520's rated at 100 V Vds and my supply is 30
> volts.
> I am careful not to exceed the V gs.
>
> The gates are driven with a toroidal transformer and the whole
> circuit is just a scaled up version of my original TX, which works fine.
> It generates healthy power into a 50 ohm dummy load but on
> connection to the aerial circuit - bang !
> The aerial system is identical to that used with the old TX !
>
> Has anyone any ideas on what's causing the problem and how to cure
> it ?
>
> I'm running out of FET's and my nerves are somewhat frayed (shell
> shock!)
>
> 73 Chris G3XIZ


This email is for the intended addressee only.
If you have received it in error then you must not use, retain, disseminate or otherwise deal with it.
Please notify the sender by return email.
The views of the author may not necessarily constitute the views of EADS Astrium Limited.
Nothing in this email shall bind EADS Astrium Limited in any contract or obligation.

EADS Astrium Limited, Registered in England and Wales No. 2449259
Registered Office: Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2AS, England