Message-ID: <537D51CB3CAC4E33812B1A81FFC73E11@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTincvq2PNPFhDEcQac6Y0tcXawhPtnP3Muh1gJZt@mail.gmail.com> <4C971B00.30705@telus.net> <004201cb58bb$529164e0$4001a8c0@lark>
In-Reply-To: <004201cb58bb$529164e0$4001a8c0@lark>
Date: Mon, 20 Sep 2010 14:01:20 +0100
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Subject: Re: LF: RF and Combustion tests, and sparking, and TVI
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Or even  worse, have  dielectric losses ....

G. 

--------------------------------------------------
From: "Alan Melia" <alan.melia@btinternet.com>
Sent: Monday, September 20, 2010 12:41 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: RF and Combustion tests, and sparking, and TVI

> 
> Of course on of the problem is likely to be that flame retardants will
> probably be banned under RoHS :-))
> Alan
> 
> ----- Original Message ----- 
> From: "Scott Tilley" <sthed475@telus.net>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Monday, September 20, 2010 9:27 AM
> Subject: Re: LF: RF and Combustion tests, and sparking, and TVI
> 
> 
>>   Hi Andy
>>
>> In Canada, to obtain a field electrical safety approval for an 'unknown'
>> polymeric or other non-metal enclosure the material must pass the
>> following test:
>>
>> Using a paper match or butane cigarette lighter apply the flame directly
>> to the material at its most vulnerable spot for 15 seconds then remove.
>> If the material continues to burn after 5 seconds it is considered a
>> fail, if it self extinguishes within the 5 seconds it is a pass.
>>
>> The above is good enough for insurance underwriters here and is codified
>> in the CSA "SPE-1000 model code for the field evaluation of electrical
>> equipment." I would suggest it be used in cases where fire is a concern
>> for amateur purposes.
>>
>> Full product certification flame tests are far more rigorous but the
>> above is considered acceptable for one of's and prototypes...
>>
>> 73 es GL
>> Scott
>>
>>
>> On 9/20/2010 8:08 AM, Andy Talbot wrote:
>> >
>> > I've carried out a few tests to see why the LF loading coil / ATU
>> > housing caught alight and I'm now just about certain it was caused by
>> > sparking from the aluminium foil used to seal the joins in the B+Q
>> > Garden Store box and not RF being absorbed by teh plastic housing.
>> > Combustion:
>> > Placing pieces of the plastic housing in a gas flame, they caught
>> > alight almost immediately and continued to self-sustain burn with a
>> > yellow flame.   The fumes given off were almost completel odourless so
>> > I'm pretty sure the material is polycarbonate - which on a reasonable
>> > assumption based on its name, contains only C, H and O, and explains
>> > why it burns moderately well.  I was rather surprised how quickly
>> > the material caught alight, and then how slow but steady the resulting
>> > flame was.
>> > Incidently, I've tried burning clear polycarbonate roofing sheet in
>> > the past, and it barely self-sustains - so I suspect the latter has a
>> > fire retardant added.   They're not going to bother with that on a
>> > cheap garden storage shed..
>> > In a microwave cooker:
>> > After several minutes of exposure, the material wasn't even warm.  I
>> > tried pieces of the black base material  and the green plastic
>> > housing, so it looks as if this material is not going to suffer any RF
>> > absorbtion effects.
>> > The 600 Watt beacon transmission  had been going for about 30 minutes
>> > (at 33% WSPR duty cycle) before I noticed anything, so it may well
>> > have started burning right at the start to end up with the result
>> > shown in those pictures.
>> > An incident in the past lends weight to the sparking idea.   Just
>> > once, a few months ago, digital TV reception was suffering
>> > intermittent interference and blocking and I realised the interference
>> > was correlated with the transmission sessions of my 150 watt 503kHz
>> > beacon signal.  Checking in the ATU showed (smelled) nothing out of
>> > the ordinary, and I put the interference down to "EMC Related issues"
>> > perhaps along the mains.  TV reception was OK the next day and ever
>> > afterwards.   On reflection, 500kHz signals have no real way of
>> > affecting UHF, so I am wondering if minute sparking was going on just
>> > occasionally, with the resulting harmonics enough to cause QRN  at UHF
>> > - with perhaps a session of dehanced propagation contributing.
>> > Conclusions.
>> > Cheap polycarbonate (probably) garden buildings from DIY centres are
>> > suitable for RF housings PROVIDED there is no sparking / direct heat
>> > exposure.
>> > Don't even think of using metal tape without soldering or properly
>> > bonding all joints - especially the sort not designed for electrical
> use.
>> > Don't set light to garden sheds
>> > Andy
>> > www.g4jnt.com <http://www.g4jnt.com>
>>
> 
> 
>