Excellent and very helpful summary Dale!
It may be worthwhile submitting that as an article to QST - such could
save many Hams, especially new Hams, a lot of grief.
And last I knew they will even send you a few diminishing-value
greenbacks for your trouble.
If not then as an article on a Web page so Hams may find it when
searching on power supplies and rfi.
73, doc
> Very good comment. I think the key word in your message is "lab". While
> not specifically intended for communications apps, lab applications can be
> very demanding as well. Good point and worth mentioning. I have only one
> caveat to add, Tom: low noise and ripple on the output are hallmarks of a
> good quality power supply - agreed. However, those are no indication of
> what is radiated from the cabinet or pushed back upon the AC power line,
> where the noise can re-radiate anyway. Specs for those parameters are very
> hard to comeby for all except military power supplies (specifically,
> MIL-STD-461.) There is some hope if a supply is certified to the IEC
> requirements and bears the "CE" mark. However, in my mind, nothing takes
> the place of actual specs from the manufacturer or published lab tests (as
> ARRL did back in 2002).
>
> True lab power supplies would (or should) also exceed FCC Part 15 standard
> requirements. I also agree with the "pound per amp" for the large output
> linear supplies. Eons ago, I worked with a few of those bricks that
> delivered nearly 100 amps - but by being designed and built in the 60's and
> 70's, they truly inspired my awe when it came to sheer size and weight.
>
> In the case of the current unit in question, I still have my doubts about
> its suitability to be anywhere near comm gear. As K9YC noted in his recent
> posting, the primary problems for emissions are in the HF region. Remember
> this about switchers (of any type): the FUNDAMENTAL switching (operating)
> frequency for modern power supplies can be anywhere between roughly 50 kHz
> at the low end and nearly 3 MHz (sometimes higher!) at the high end. Most
> utility supplies seem to operate in the region of about 100 kHz to 450 kHz.
> Potential buyers must understand that the LF and MF bands (including the AM
> broadcast band and 160m) are likely to be in either the operating range of
> the switcher of within the lower order harmonics. Lab supplies and those
> made for comm applications include extra filtering, by-passing, and care in
> design over utility supplies. That's where the performance comes from -
> more parts, better design, more cost. (As one very prominent EMC
> consultant is fond of saying, "The way to spell "EMC" is "$".)
>
> One more thing: A utility 12 V power supply (such as the one in question)
> may very well deliver just that: 12 VDC. It might have a voltage
> adjustment control on it somewhere, but it's almost a given that some work
> would have to be done to set it for a nominal 13.6 VDC output. (A common
> design criteria is to have an output adjustment range of +/- 10%. That
> means a supply designed for 12.0 VDC output would have a max adjustment
> range of +/- 1.2 VDC, making 13.2 volts the most you could get without
> having to change a part or two.)
>
> 73, Dale
> WA9ENA
>
>
>
>
>> [Original Message]
>> From: Roger (K8RI)<k8ri@rogerhalstead.com>
>> To:<rfi@contesting.com>
>> Date: 11/6/2010 12:59:24
>> Subject: Re: [RFI] Anyone know if this 12v ps is RFI-clean?
>>
>>
>>
>> On 11/6/2010 12:31 PM, Dale Svetanoff wrote:
>>> Doc,
>>>
>>> I've said it before and I'll say it again: unless a power supply is
>>> designated specifically for communications applications, assume that it
> is
>>> NOT "clean enough" for communications usage.
>> I purchased a 40A lab supply at a very good price, (one Doc mentioned
>> earlier) with digital read out it took a bit of testing but it turned
>> out to be well regulated, and clean. Which BTW is also a switching
>> supply. Those big "conventional" supplies run just about a pound per
> amp.
>> The specifications for the PS will tell the story. There are many good
>> switching supplies out there, and there are a lot more that are not
>> suitable, but when you get ripple and noise figures in the 0.1% they are
>> likely pretty good.
>>
>> 73
>>
>> Roger (K8RI)
>>> The unit in question is
>>> almost surely a switcher, and if intended for commercial applications,
> it
>>> will only meet FCC Part 15 Class A emission specs, which are several dB
>>> worse (higher) than the Class B requirements for computers and digital
>>> equipment used in the home. (Note that the seller is including
> shipping in
>>> the $50 price - that tells me that the unit is light weight, virtually
>>> guaranteeing it to be a switcher.)
>>>
>>> For truly "clean" power, get a "hernia-maker" - meaning a linear power
>>> supply, not a switcher. You only have to worry about 60 or 120 Hz hum
> and
>>> ripple with those. If you don't want big iron like that, then stick
> with
>>> the select group of switchers that are designed for communications
>>> applications. Those units will exceed performance of FCC Class B
> equipment
>>> by controlling both the radiated and conducted emissions. Yes, you will
>>> pay more, but you get what you pay for.
>>>
>>> If you watch closely, there are surplus equipment dealers (and people at
>>> hamfests) who sell off big linear power supplies very cheaply. They
> were
>>> the norm 20 or 30 years ago, and you can probably get one for under $50.
>>> You'll want to find it locally, however, as these babies usually weigh
> 40
>>> pounds or more when you start talking 50 amps (or greater) output
> current.
>>> Unless malfunctioning, they usually deliver clean power to the loads.
>>>
>>> 73, Dale
>>> WA9ENA
>>>
>>>
>>>> [Original Message]
>>>> From: doc@kd4e.com<doc@kd4e.com>
>>>> To: RFI List<rfi@contesting.com>
>>>> Date: 11/5/2010 9:35:04
>>>> Subject: [RFI] Anyone know if this 12v ps is RFI-clean?
>>>>
>>>> Anyone know if this 12v ps is RFI-clean?
>>>>
>>>> "12 Volt 47 Amp Power supplies"
>>>>
>>>> See picture here:
>>>> http://swap.qth.com/view_ad.php?counter=866425
>>>>
>>>> It looks like some sort of modified surplus server PS.
>>>>
>>>> I have asked the seller a couple of times but no clear
>>>> answer yet. Does it look familiar to anyone?
>>>>
>>>> --
>>>>
>>>> Thanks!& 73, doc, KD4E
>>>> http://KD4E.com
>>>> Have an http://ultrafidian.com day
>>>> Defend free speech or lose your freedom.
>>>> I don't google I SEARCH! http://ixquick.com
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>>>
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--
Thanks! & 73, doc, KD4E
http://KD4E.com
Have an http://ultrafidian.com day
Defend free speech or lose your freedom.
I don't google I SEARCH! http://ixquick.com
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