[RFI] New switching wallwarts - RFI potential?

[Roger (K8RI)]

Paul Christensen wrote:
>> "...The mechanism that causes all of that noise is the rectifier diodes. 
>> If you use diodes that have a long minority carrier lifetime, no problem, 
>> but with the faster diodes that are being used nowadays..."
>>     
Short minority carrier lifetimes?  The whole semiconductor industry is 
devoted to reducing minority lifetimes and high lifetimes are an 
indication of poor semiconductors that are impure.

We used to measure lifetimes with a zenon flash source and around a 7 or 
30 MHz signal across the crystal using HP rack mounted scopes with P7 
(High persistence phosphors).  I built up a system using a storage scope 
which basically eliminated the need for the lab tech to visually 
interpret the decaying trace, or multiple traces that were seldom in the 
same place even with the high persistence phosphors. The storage scope 
worked great as you could get a single trace and position it properly on 
the screen  overlaying the curve.

73

Roger (K8RI)
>
> That's a new one on me.  I had not heard of RFI/EMI generated by PN junction 
> switching in linear-mode power supplies.  In reading through Dallas 
> Lankford's description, I was initially certain he was discussing a Radio 
> Shack switch-mode supply until I saw the simplicity of the circuit in the 
> photos.
>
> What types of short minority carrier lifetime diodes are the culprits and 
> why are they now being used in linear power supplies in place of the 
> garden-variety 1N400x types?
>
> Paul, W9AC
>
>
> ----- Original Message ----- 
> From: "Martin Ewing" <martin.s.ewing at gmail.com>
> Cc: "RFI List" <rfi at contesting.com>
> Sent: Tuesday, January 12, 2010 11:08 AM
> Subject: Re: [RFI] New switching wallwarts - RFI potential?
>
>
> Interesting about LF EMC, but no info on the new switching supplies.
>
> I have done no serious tests, but so far have not seen any issues with
> the new generation mini-switching wall-warts -- and they are really
> proliferating around here.
>
> 73 Martin AA6E
>
> On Tue, Jan 12, 2010 at 10:53 AM, Tim Duffy K3LR <k3lr at k3lr.com> wrote:
>   
>> Hi Pete!
>>
>> Here is a great paper on wallwarts.
>>
>> http://www.kongsfjord.no/dl/Antennas/Low%20Noise%20Active%20Antennas%20AC-DC
>> %20Power%20Supplies%20II.pdf
>>
>>
>> 73,
>> Tim K3LR
>>
>> -----Original Message-----
>> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
>> Behalf Of Pete Smith N4ZR
>> Sent: Tuesday, January 12, 2010 9:36 AM
>> To: RFI List
>> Subject: [RFI] New switching wallwarts - RFI potential?
>>
>> Recently, I have begun receiving a new type of wall-wart with various
>> pieces of consumer equipment and, most recently, with my QS1R SDR. Ones
>> I've seen have generally been for 5 volts at 1 amp, are much lighter
>> than the old ones, and I even got one that said Switching Adapter on the
>> side.
>>
>> It also claimed, of course, to be FCC approved and UL listed, but no CE.
>>
>> These adapters are very attractive - in addition to the high current
>> rating they are narrow, so that 6 of them would fit on a 6-hole surge
>> suppressor, even without wall-wart-spaced outlets. but I'm a little
>> concerned - I don't think I'm hearing mine, but my shack is a long way
>> from my antennas.
>>
>> Has anyone had occasion to test these critters?
>>
>> --
>> 73, Pete N4ZR
>> Visit the Contesting Compendium at http://wiki.contesting.com
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>> www.conteststations.com
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>>
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>>     
>
>
>
>