Pete et. all,
For as good as the Samlex 1235 switching power supply is I had an
instance where interference from them was heard.
Take a look at
http://www.w0qe.com/RF_Interference/Samlex_SEC1235%28M%29_DC_power_supply.html
The conducted levels of interference were way better than the recent
group of supplies reviewed in QST for the original Samlex 1235(M).
After I was done with them they were even better. To be fair to the
Samlex supplies I only heard interference when the supplies were very
lightly loaded.
73,
Larry, W0QE
On 1/16/2012 3:16 PM, Pete Smith N4ZR wrote:
> OTOH, you do have to wonder how hard it was for their reviewers to
> contain themselves from saying "this thing is junk." The numbers and
> scope displays are pretty terrible. AD5X's review of the Samplex 1235M
> is worth comparing to those units.
>
> 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
>
>
> On 1/16/2012 4:34 PM, Dale Svetanoff wrote:
>> Folks,
>>
>> As most of you know, the topic of RFI issues with switching (or "switch
>> mode") power supplies pops up here quite frequently. I was delighted to see
>> that the February issue of QST addresses the subject with lab tests on 4
>> more such power sources. (See pages 56 thru 59 for all of the details.)
>> Make certain that if you are interested in noise issues with switching power
>> supplies, you read the entire article carefully. It is also worthwhile to
>> track back and see the prior power supply test articles the League has
>> published, and which are referenced in the footnotes.
>>
>> Keep in mind that all switch mode power supplies have both radiated and
>> conducted emissions. The name of the game is to buy those having the lowest
>> levels of emissions in YOUR operating frequency bands of interest. Thus,
>> study the plots and tables well if you are primarily an HF operator, as most
>> of the emissions occur in the HF bands. (An exception was the TenTec
>> supply, which was very noisy in the 160m band, considered to be MF.) Those
>> who operate with HF antennas inside their houses (especially in the attic)
>> or with antennas close to the house and the house wiring is not shielded (no
>> conduit or metal armor cladding), might very well end up with RFI issues
>> from a power supply when trying to receive weaker signals in some of the HF
>> bands. While there are ways to reduce conducted emissions from the power
>> supplies, the best alternatives might be to either stay with linear (heavy)
>> power supplies or to move the antennas further away from the house wiring.
>>
>> Related comment: This reflector also gets frequent posts regarding
>> industrial switching power supplies for use in amateur radio applications,
>> especially for 28 VDC output or very high current at 13.6 VDC. If a power
>> supply was intended for the industrial or commercial market, the most it may
>> have to meet in the way of emissions requirements is set forth in FCC Part
>> 15, Class A limits. These limits are far more lax than the Class B limits
>> for computing devices used in a home or office environment. In short, such
>> switching power supplies are almost guaranteed to be "screamers", expecially
>> in the HF region. Stay with linear technology supplies unless you are
>> prepared to test and design filters or RFI suppressors for these special
>> power units. The cost of the "fixes" could easily add up to the purchase
>> cost of the power supply alone, or even exceed it.
>>
>> My thanks to ARRL for another excellent article in helping hams make better
>> buying decisions.
>>
>> 73, Dale
>> WA9ENA
>> _______________________________________________
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>>
>>
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