Re: LF: VLF G3XIZ - QRT

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi Chris,

You are using a class D PA? Maybe you don't even need a output transformer if you apply a coupling winding on the coil.
Why are the FETs blew up? Overvoltage or overtemperature? And what types of FETs are you using?

73, gl

Stefan/DK7FC

Am 23.11.2010 13:57, schrieb Chris Osborn:

Hello Stefan / LF,

 

All was going last night well until I heard sparking from the aerial distribution box each

time the carrier was turned off.

 

After about 45 minutes the PA FET's blew up.

 

I did some investigation and found that the output transformer has developed some

short-circuited turns and so is now useless.

 

The loading coil seems unharmed so once I get a replacement transformer and connect in some

new FET's I'll be back in business.

 

I'll slow down the rise and fall times of the pulse train from the driver unit to the FET's and hopefully cure the sparking.

 

(Mal)

Yes, N.O.V. holders must get prior permission before they transmit and must stay by the telephone for the duration.

 

Thanks to all those who looked for my signals.

 

73

Chris G3XIZ

 

 

---

From: Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Mon, 22 November, 2010 21:32:28
Subject: Re: LF: VLF G3XIZ - QRT

Hi Chris,

Sorry to hear that. Just checked to mails after beeing abscent the weekend and wanted to wish good luck too now but just read your mail below.
I assume the breakdown immediately de-tuned your system which reduced the HV? So the damage is limited to a few turns? Has it happened at the 0.2mm dia wire?
BTW i am using 0.4mm dia wire, so not really much more...

Good luck in the next tests!

73, Stefan


Am 22.11.2010 22:15, schrieb Chris Osborn:

Thanks for looking Roger and chaps but game's over for tonight.

I've insulation breakdown somewhere in the aerial circuit and I can't fix it until daylight.

Maybe try again next weekend.

73 Chris G3XIZ

---

From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org; Chris Osborn <g3xiz@yahoo.co.uk>
Sent: Mon, 22 November, 2010 20:49:24
Subject: Re: LF: G3XIZ - no copy yet on 8.9719kHz

Just swapped from the loop to the earth electrode - band noise stronger - and there may be a hint of a signal on Chris's frequency.

73s
Roger G3XBM

On 22 November 2010 20:21, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

Have been looking for 20 minutes so far but nothing seen from Chris at about 34km distance.

Will continue to look for the next 2 hours.

73s
Roger G3XBM

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088