The AM Forum

I bought a new Dell in Feb of 2006. It had the nastiest power supply. It pretty much made AM listening on 75 and 160 miserable. I never replaced it because I figured they were all pretty much the same. Following up on some discussion on this board about a month ago I bought an Antec supply and installed it this morning

This is a screen shot this morning of the SDR before and after I changed it out and after. HUGE difference.

Thanks to all who suggested it.

73
Carl
/KPD

Nice Carl. 

I hate switching supplies.  Mainly due to low quality. Newer Astron stuff is complete garbage.  I got a 30 amp switcher astron a while back.  It through S9 on 3870.. LOL.  It also through out crap over the 40 meter band. I went to the older transformer style power supply and the problem is gone.

Clark

 Yes, but those with active Power Factor Correction (PFC) are much quieter, and usually more efficient. The Antec Carl bought has active PFC. Good stuff.

Jim
WD5JKO

I have an enermax 650 in my main PC.  I had 8 Hard drives in it.  Never heard it over my HF rigs.  So add that to the list of Good supplies.

C

The old style switchers typically take the AC line voltage, rectify it, filter it (large capacitance), and then have DC to DC conversion to the various outputs needed. The rectifying and filtering is "capacitor input filtering" where the current draw is in short and massive current spikes every half cycle. When the supply is high power, this approach pollutes the AC supply (squishes the peaks), and generates a "comb generator" like hash with two pulses every line cycle.

[Side note: big high power Ham linear amps with full wave voltage doublers also cause AC line peaks to compress, hence the need for large Awg and short wire runs.]

The "active PFC" approach in a way acts like a "choke input" filter where the current is continuous, sinusoidal, and in phase with the voltage. Instead of using a big L-C, this is done with some pretty nifty high-tech circuitry. Active PFC has been around for decades, but not cost effective until recently.
   
The following link gets into the bells and whistles of how active PFC works:

http://powerelectronics.com/ar/PFC-design-standards/

"Existing PFC Technologies An ac-dc converter circuit with ideal PFC draws a current that is proportional to the instantaneous voltage of its ac source. With a sinusoidal voltage input, the current drawn should also be sinusoidal and in phase with the voltage. Many PFC technologies have been developed through the years, and they fall into three categories: passive, active and single-power stage with PFC."

Jim
WD5JKO

I am afraid I may be getting some interference from a nearby switching power supply.  It sounds just like power line noise, and seems emanate from all the poles near the house.  It solidly covers the hf spectrum from 160m to 10m, but there is no trace at VHF on my AM aircraft receiver I use as a noise sniffer.  I have never before experienced line noise on HF that didn't also register on VHF-AM as I approached the poles, therefore I am wondering if it is being generated in one of the nearby houses and leaking onto the power lines via the mains connection.

That certainly might be possible Don, however, consider that it still could very well be a faulty powerline component. When I experienced severe line noise at my location 2 years ago, the power company was stumped at first, since the noise seemed to be everywhere in the area. It took the technician 3 days to locate the source, which was approximately 3/4 of a mile away, across the river, in another town, on a typical 13.3kv neighborhood type line that was running through the woods. In my case it was a blown lightning arrestor that was arcing continuously. In my attempts to locate it, I used google maps and a 6 meter and 2 meter beam heading. As it turns out, when I put a ruler down on the map, lined up with my beam heading, it intersected the pole almost perfectly. The problem was that the noise was so strong at my location, the technician dismissed the idea that it could be that far away. Hope you find it!

Glad you found the solution to the noise Carl. I have had excellent results with Antec and Enermax supplies. Unfortunately, many of the cheapo OEM supplies are missing the internal filter components. Inside the supply, instead of chokes on the PS board at the line input, you are likely to see jumpers. Wonder how those slip through "inspection"?

I just found a source of RFI here. I was given a cell phone and charger for work. When it is plugged in and charging there is a rhythmic steam engine type noise that emanates from it.(wall wart I assume is a switcher).  I'll pull that one out when not in use, until I get a snap on choke for it.

I'm swamped in noise.  Swimming in it.  Tonight, even the MFJ noise canceling box couldn't really get rid of something that is broad and nasty and all over 160 and 80.   Most of the time the MFJ phasing box makes it possible for me to operate.  I was talking to W9AD yesterday about noise and noted that I wish I were back in the days when I only had arcing power line noise to deal with.  At least it is broad up into VHF and somewhat consistent.   The appliance noise changes character, has a modulated characteristic to it, may jump around or be sporadic...and doesn't get into VHF where my hand held airband rx can find it. 

I got a Grundig Yacht Boy 400 portable sw rx on eBay today.  Going to put that thing on 75 meters and walk around and see if it will help me close in on the sources of noise.  There are several.  If not I can always use it to listen to the NoonTime Forum on 3870 on my lunch hour at work.   I hope the problems are all wall warts that are easy to replace assuming linear supply w.w. are still available.

RF noise from consumer electronics seems to me to be a major operating impediment yet I never see anything about it in any of the ham periodicals.  Surely I am not the only one surrounded by unintentional emitters. 

My elmer and good Friend George built an ultra sonic detector. His property has large power lines and had horrible noise on HF. After building this, he located the problematic insulators. The power company came out and after showing the tech the problem, They replaced the insulators. Noise gone.

Scroll down to see pictures of it.

Clark

http://www.arizona-am.net/PHOENIX/W8QBG/Bauer/project2.html