Re: LF: WSPR Beacon -RIP

[Andy Talbot <andy.g4jnt@googlemail.com>]

I think the metal tape is the answer.   It was never there to serve any electrical purpose, but seemed ideal at the time to waterproof the gaps in the rather crude press fit construction   It was the stuff designed for sealing heating and air conditioning ducts, plastic backed so definitely did not make good electrical contact wher eit overlapped.  Right at the base where the fire was at its fiercest, the residual tape is close, and was probably touching, the thick copper earthing wire that went around inside.   Its quite likely it started sparking at this point and once the plastic was charred, it just started absorbing more energy.

 

Not sure what the plastic material is, but the fumes, though potent, weren't too bad and the smell was something like burnt polycarbonate.

 

For the replacement, think I'll return to the plastic dustbin idea that served so well before, but make a better support inside with easier access to the variometer

Andy
www.g4jnt.com

On 19 September 2010 13:03, Graham <g8fzk@g8fzk.fsnet.co.uk> wrote:

Sorry to see  that Andy,

 

The metal  tape looks suspicious, damage  very intense at the lower  far  corner , shelf is most probably heat damage  from the  fire as under the  coil looks intact ?

 

I for  one will  be having a quick look in the shed, round the  500 atu  make  sure nothing is 'too' close

 

G.

 

 

From: Andy Talbot

Sent: Sunday, September 19, 2010 12:22 PM

To: rsgb_lf_group@blacksheep.org ; jfell@tesco.net ; Julian@ygf.org.uk

Subject: Re: LF: WSPR Beacon -RIP

http://www.g4jnt.com/QRO_LF_DoesThis.JPG 

http://www.g4jnt.com/Melted_ATU_Cabin.JPG
 

Not sure what started burning, but it was in the bottom corner by the look of things which is well away from the high voltage stuff at the top.  

 

The system ran for years using a plastic dustbin as the coil housing, even at 800 Watts occasionally.  But from the way the shelf has melted, it looks as if the plastic used in those B+Q sheds absorbs RF.   Pity, it was going to house HF ATU

 

 

Andy
www.g4jnt.com

2010/9/19 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Andy,

QRO can be an exciting adventure! :-)

73, GL,

Stefan



Am 19.09.2010 12:54, schrieb Andy Talbot:

Well, it was nice while it lasted.  Went downstairs and smelt smoke.   Heard a crackling noise coming from the plastic "shed" housing the ATU .   Opened the door, saw flames and melted plastic.

 

Two buckets of water before they were extinguished - plastic B+Q sheds burn very well

 

Goodbye antenna tuning cabin :-(

 

The loading coil and antenna survived.   My credibiilty didn't  :-(

 

Pictures will follow

Andy
www.g4jnt.com

On 19 September 2010 11:44, Andy Talbot <andy.g4jnt@googlemail.com> wrote:

Sinece theere were no reports of my QRP WSPR beacon last night two conclusions can be drawn :

 

a)   No One was listening

b)   Its too weak.

 

To resolve   a) ...... ??  Not a lot I can do apart from post this message :-(

 

But to resolve b), I've now fired up the big switchmode PA   http://www.g4jnt.com/137tx.pdf      

Generating about 600 Watts this will increase ERP into the region of  17dBm

(The WSPR message says 13dBm, but its lying. I've already run up and downstairs with the PIC programmer, and don't want to do it again)

 

 

Andy
www.g4jnt.com