Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org)
Message-ID: <44567AEF.30800@wp.pl>
Date: Mon, 01 May 2006 23:17:35 +0200
From: Marek SQ5BPM <sq5bpm@wp.pl>
User-Agent: Thunderbird 1.5.0.2 (Windows/20060308)
MIME-Version: 1.0
To:  rsgb_lf_group@blacksheep.org
References: <253.a04dd5e.3187c56d@aol.com>
In-Reply-To: <253.a04dd5e.3187c56d@aol.com>
Subject: Re: LF: EMF sensitivity?
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Hello John and thank you for the reply.

WarmSpgs@aol.com wrote:
> Marek, I am not aware of effects like yours being reported from 
> exposure to much stronger LF fields at LORAN sites and other 
> transmitting facilities.  The magnetic field 2 meters from a loading 
> coil handling 500 watts might be near or slightly above accepted 
> limits for human exposure at low frequencies, but not greatly in excess.
That's what I thought about. Polish Radio 225 kHz transmitter had 2 MW 
of power and the staff has been working quite close. You probably know 
the story about it's 646m-high mast collapse in 1991 due to a human 
error during conservation.
> However, as you surmise, you are not just being exposed to LF alone. 
>  
> The two middle items on your list are, far and away, the most likely 
> sources.  In addition to the normal high-frequency components of the 
> switching waveform, it is possible for there to be surprising amounts 
> of UHF energy from parasitic oscillations during the on/off 
> transitions of the FETs.  This depends a lot on circuit layout.
I will check waveforms inside the circuit, but there cannot be too much 
power generated at high frequencies, because the power balance would be 
wrong. But, probably, I am unlucky and there is some kind of resonance 
at a few hundreds MHz and most of the oscillations concentrate at that 
range.
> Your symptoms sound very much like a story I heard in my younger days 
> of an amateur radio operator whose unshielded high-power HF rig was 
> emitting parasitic oscillations in the high UHF range.  He, too, 
> experienced a rash and other allergy or flu-like symptoms, and 
> eventually developed eye problems.  I would very much encourage you 
> shield the rig adequately before further operation!
Yes, that is the general plan, to move the whole TX to a new, 
better-designed enclosure. The current arrangement leaves too little 
place for the airflow, that's the only reason why the top cover is 
removed...

I also heard a story about some jerk tuning an open 2m 1kW PA until a 
blood started to flow from his nose... Fortunately, no bloody symptoms 
here so far ;)

73! Marek SQ5BPM