Actually, mumble mumble years ago, I worked on switchers that had, for all
intents no measurable noise in both the RE and CE range of test from Mil-810.
Of course the USN was spending major money for rack steel cased, mu metal
wrapped, hand tweaked power supply we shipped. Spend enough and you would be
surprised how quiet a switcher you can make
73 de KG2V
> On May 4, 2016, at 5:59 PM, Doug Powell <dougp01@gmail.com> wrote:
>
> There is no such thing as a "noise free" switcher, only unaffected
> equipment. The quietest switching power supplies tend to be medical grade.
> You don't want RFI affecting life support equipment.
>
> All switchers pull pulses of current from the rectified AC Line at
> frequencies of a few kHz up to 1 Mhz. While this fundamental switching
> frequency and mostly odd harmonics can be part of the problem, the real issue
> is the reverse recovery time of the diodes and the storage time of the
> switching transistors. These times can be from a few microseconds down to 100
> nanoseconds or less. The reciprocal of these recovery times is basis of the
> frequencies and the harmonics they produce. Switch-mode power supply
> designers are always pressured for higher and higher operating frequencies
> and faster recovery times in order to shrink physical size and improve
> efficiency. Just think about to latest generation of USB 3.0 power packs
> and how small they are for the amount of power they produce.
>
> The high frequency pulses produced by bipolar transistor designs can easily
> have a fourier content in the 150 kHz to 30 MHz range. The MOSFET type
> switchers can typically produce additional frequencies from 10 MHz on up to
> more than 300 MHz. The stuff in the low end tends to be narrow band emissions
> and the stuff on the high end tends to be broadband noise, for the most part.
> Standard emissions testing these days set limits in a range from a few 10s
> of kHz to 3 GHz and sometimes higher.
>
> So the bottom line is to find a power pack with a noise profile that works in
> your application. If it is of interest to the group, I may be able to pull
> up some old plots from a spectrum analyzer, just to show what I mean by
> "noise profile".
>
> All the best, ~ Doug
>
>
> Original Message
> From: WD8ARZ
> Sent: Wednesday, May 4, 2016 3:15 PM
> To: rfi@contesting.com
> Subject: Re: [RFI] DC Power supplies
>
> AC switching type power supplies tend to be very rfi noisy. Transformer
> type power supplies dont use the the dc to ac to dc switching that
> generate that RFI .... and should be quieter power supplies. They are
> heavier, with line isolation in most cases, and worth the extra expense
> and weight. Another bad trait for those switching power supplies is that
> there is generally not a true physical break the utility power feed
> switch. Instead they just disable the output and leave the switching
> circuits active and thus are RFI sources as long as they are plugged in.
>
> 73 from Bill - WD8ARZ
> South Bend, Indiana
>
>> On 5/4/2016 2:51 PM, charlie@thegallos.com wrote:
>> Hey Gang,
>> We all know about buying old analog wall warts for power supplies to cut
>> down on RFI, but sometimes, that is NOT going to happen
>>
>> snip snip
>>
>> I think it might be a real good idea if we could come up with a list of
>> various "Line lump" (so they can be wired in) type power supplies at
>> various power ratings that are KNOWN to be good, and sources for them
>>
>> I'd be more than happy to collect the list and put it up on my web site
>>
>> 73 de KG2V - Charlie - www.thegallos.com
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