FWIW, my experience with switching LV power supplies of various kinds has been
that the RFI they generate is common-mode. I've had no luck suppressing any
noise from them with differential filters. That's just an anecdotal data point,
nothing more -- not a theoretical opinion. :-)
I've also had the experience with LV halogen lights that some of the switcher
PSes clearly do not meet any standard for RFI, generating S9+ hash over the
entire HF-VHF spectrum, while many others are completely clean. The difference
is always huge -- they either do it or they don't. Makes me think that some
manufacturers simply figure to get away with it and save big money on filtering
components -- and apparently do so with relative impunity, since the devices are
on the shelves and people buy them. After all, what percentage of typical
consumers would even know or care about HF-VHF RFI from halogen PSes? Much less
than 1%, probably much less than 0.1%, is my guess. The cost of refunding to
their retailers for the occasional return is probably far less than the NRE and
component costs of doing it right would have been.
Bill / W5WVO
Jim Lux wrote:
> ----- 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?
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
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_______________________________________________
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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