[HCDX] Re: [HCDX]: R.F. NOISE

[Vittorio De Tomasi <vdetomasi@xxxxxxxxxxxxx>]

Patrick Martin wrote:
> 
> Does anyone know what the noise sounds like from the new RF light bulbs?
> For the past month I have been getting a "buzz" from just before LSS to
> about LSR. Once in a while thenoise has been on all day. I main affects
> my Northern beverage, but it also gets into my EWE antenna. With the
> Drake R8 this evening after it popped on I checked the band from 100 kHz
> on up. I lost it at about 3-4 mHz. It isn't bad on many places on the
> dial. I hear varied  tones from 100-200 kHz, and as you go higher,the
> harmonics seem to be more of a "buzz". One strong one at 760 kHz and
> others 1000-1200 kHz.
>    At first I thought it was powerline noise, but with the timing it
> would not be that and the varied tones, it much be something else.
>    Anyone have any ideas?
> 73s,
> 
> Patrick
> http://community.webtv.net/BobAndPatrick


Hi Patrick,

as far as I know, RF light bulbs (sulphur lamps) are powered by
microwave energy, and they have probably little to do with the noise
affecting you. 

Are you sure that the noise is not coming from a faulty HID lamp (High
Intensity Discharge - not to be confused with halogen lamps) ? They are
often used for street and industrial plant illumination, and they are
basically arc lamps, whose arcing is controlled by a current limiter
(ballast). Together with the power lines they can behave as a spark-gap
transmitter, if the current limiter is faulty. Besides radiating on the
frequencies where the power lines resonate (the "buzz" emission), they
emit also plenty of noise (some months ago one of these faulty lamps
close to my QTH emitted a noise spectrum till to 1.1 GHz !). The "buzz"
they generate is usually in the range of LW-MW bands, and can drift in
frequency due to arc voltage variation, or if power line length varies
(it is often enough to open/close a mains switch connected to the power
line, to have the "buzz" drift of several kHz).

To approximately locate the source, you can use a MW receiver with a
loopstick ferrite antenna. You will probably not be able to find exactly
them, because the low-frequency "buzz" is usually spread everywhere by
power lines.

To circumvent this problem, and to exactly pinpoint the position of the
faulty lamp, I used succesfully a portable scanner with AM/SSB detector,
and a small dipole antenna (but a TV VHF yagi could work too). The VHF
noise emitted by the lamp is not "captured" by power lines, and locating
the faulty lamp becomes a straightforward fox-hunting game...

WARNING: do not ever think to repair the faulty HID lamp by yourself,
unless you exactly know what you are doing. The lamp ballast delivers at
start up a voltage pulse of about 1 kV, that can instantly kill a man. 

More on HID lamps (and RFI emitted by them) at http://www.misty.com/~don

vy 73

Vittorio IK2CZL

-- 
*************************************************************************
Vittorio De Tomasi         ik2czl@xxxxxxxxx
Home page:                 http://space.tin.it/scienza/vdetomas 
My DSP page:               http://www.freeyellow.com/members/padan

"Wir muessen wissen; wir werden wissen" (David Hilbert)

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