It is definitely a switcher, Dale. I didn't know for sure, but kinda
figured that was how they achieved the wide input voltage range on these
things. That, plus the weight hi.
73, Pete N4ZR
The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
On 2/29/2012 4:36 PM, Dale Svetanoff wrote:
> Pete,
>
> Very interesting, but one big question: You say that the Radio Shack wall
> wart is regulated. OK, is it linear or switcher? One way to tell without
> cutting or sawing it open is to look at the power input requirement. If it
> says "120 V" only, then it is likely a linear regulator (with an input
> power transformer, rectifiers, a few filter caps, and a 12V regulator chip
> or circuit). If it says something like "90 to 240 VAC", then it is
> guaranteed to be a switcher and everything you wrote makes sense.
>
> If it is a linear, I do know of a few instances in which linear regulator
> chips (such as LM7812, or equivalent) "took off" as oscillators because
> they were not properly by-passed at their input and/or output pins. A
> properly functioning linear regulator should not contribute to the noise on
> your system.
>
> 73, Dale
> WA9ENA
>
>
>> [Original Message]
>> From: Pete Smith N4ZR<n4zr@contesting.com>
>> To: RFI List<rfi@contesting.com>
>> Date: 2/29/2012 10:58:07
>> Subject: [RFI] Common mode noise
>>
>> I just built a bias-tee to inject 12 volts into my receive antenna
>> feedline for a relay box and preamp at the far end. I used what I think
>> is a standard design, with a series 1 mH RF choke and an 0.1 uF bypass
>> capacitor to prevent RF ingress from the DC line coming into the tee.
>>
>> To my surprise, with no antenna connected, the 160M background noise
>> level in a receiver connected to the tee was still several S units
>> higher when the DC supply (a Radio Shack regulated wall wart) was
>> connected than when it was removed.
>>
>> I had a #31 core handy, so I wound 10, then 15, then 20 turns of the
>> parallel wire from the wall wart to the plug on the end. This
>> progressively reduced the noise being contributed by the wall wart to a
>> level such that I now cannot hear the DC supply on any band above 160
>> meters.
>>
>> I just thought this might be useful info for someone else out there, and
>> I'd also appreciate any critique of the methods I used.
>>
>> --
>> 73, Pete N4ZR
>> The World Contest Station Database, updated daily at
> www.conteststations.com
>> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
>> spots at telnet.reversebeacon.net, port 7000 and
>> arcluster.reversebeacon.net, port 7000
>>
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>
>
>
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