On 11/6/2010 2:51 PM, Dale Svetanoff wrote:
> Roger,
>
> Very good comment.
Thanks
> I think the key word in your message is "lab".
Agreed.
> While
> not specifically intended for communications apps, lab applications can be
> very demanding as well.
This was actually a fairly expensive supply listed at $300 on sale for $99.
The output voltage is adjustable and when set to 13.8, stays at 13.8
from zero load up though 30 amps which is the highest I've run it.
I hooked it up to the 756 pro using about 6 or 8' of RG-8X with about 6"
on the end left unshielded. I used the unshielded end as a probe around
the cabinet and power cables (in and out) while listening to the ham
bands 160 through 10 (and watching the display). I could neither hear
nor see anything from the PS *except* for a single, very weak birdy at
start up. I heard it on 75 meters as it shot by and across the screen
never to be seen or heard again.
> 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.
Years ago I picked up several of the old process control computer power
supplies and even a pair of Westinghouse P2000 computers at a surplus
equipment auction where I used to work. One with 16K and the other with
32K of "core" memory that looked like a bad backlash on a bait casting
reel. Those power supplies almost took two men to lift. One could do it,
but certainly not conveniently. We mounted one on the outside of a 6'
rack cabinet to power the repeater back in "the old days" When I say
"old days" I really do mean "old days". All the hams in the photos are
about 40 to 60# less than they are now. There were IIRC four hefty
transformers with rectifiers and pass transistors in there and the leads
were #6. Of course we were using the receiver section of an early Icom
synthesized rig, with a preamp in front of that. The transmitter, I've
forgotten other than it was crystal controlled as the signal from a
synthesized rig wasn't clean enough to use in full duplex even with 6
cans. The exciter had an amp behind it. So we were running far more
sensitivity than the commercial rigs and as much power as we were
allowed. I remember working that repeater from the parking lot at one of
the MSU dorms to just South of Houghton Lake. Needless to say it was a
"regional" system.
I also picked up a pair of RF induction heating generators that ran 6 KW
out. One of the locals used the guts to build an amp using a 4-1000
inside the big steel cabinet that was about 3'W X 4'H X 4' D. One of
them on the back of a little S-10 pickup was enough to make it "stand
up". I had noted that on the way home " the front end seemed light".
Once we rolled the generator toward the back of the truck the front
wheels were almost 5' off the ground. Good thing the load didn't
shift<:-))
> 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 "$".)
Depending on the source, what a ham has in the junk box, and their skill
level, taming one of these ranges from easy to impossible.<:-))
At $99 I purchased the 40A supply on speculation and figured I could
experiment if need be. Fortunately it turned out to be a good supply.
73
Roger (K8RI)
> 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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