----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <towertalk@contesting.com>
Sent: Thursday, November 25, 2004 12:16 PM
Subject: Re: [TowerTalk] Halogen Bulbs - 1.8 Mhz RFI
> On Thu, 25 Nov 2004 14:46:07 -0500, Floyd Sense wrote:
>
> >I doubt that there is much you can do to silence them.
>
> I agree that there are probably switching supplies causing the problem,
> but I wouldn't give up on fixing the problem without trying.
>
> There are three basic ways the RF can get out -- on the power line
> wiring, on the low voltage wiring to the lamps, and direct radiation from
> the power supply if it is unshielded. Direct radiation you probably can't
> fix except by replacing the supply. A standard, good power line filter
> should eliminate what is coming via the power line, and a multi-turn
> choke around a big ferrite, possibly in combination with a capacitive
filter
> should be able to kill what is on the low voltage wiring.
>
> You will need at least 8 turns around the typical big toroids to make an
> effective choke for 1.8 MHz. That choke should also work on 80 meters,
> but may be running out of effectiveness by 40 meters and above.
>
> 73,
>
> Jim Brown K9YC
>
>
Depending on where the noise is coming from, a common mode filter
(i.e.running a bunch of turns of the twoconductor wire through a ferrite)
might not help a lot. You might need a decent differential mode
choke/capacitor filter on the output of the low voltage supply. Put the
choke first (so the capacitive load doesn't screw up the switching
regulator).
Also, if you have a LV halogen scheme with the two "rails" from which the
lamps hang, the rails can serve as a nice radiator of differential mode
noise.
By the way, if the halogen power supply is a low voltage device, it would
need to comply with EN55011 (the EU equivalent of Part 15). Perhaps the
problem is really that the halogen supply isn't working to spec?
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