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Weird Observation on Solid State Power Supply

Wire Weasel

Senior Moment
Dec 13, 2008
2,953
589
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Posted this occurrence on earlier thread. Noticed several months ago when running my HF rig on the Megawatt S12 400 I think it is .... the 36 amp one, that it was spewing spurious noise every 5-8kc between around 15-23mhz making those freqs nearly unusable. Mainly took away 15 Meters from me. Otherwise was no problem in the other frequency areas. Okay - now the setup was in an outbuilding workshop being fed by 125' feet of extension cord from the house. Web searches indicated that others have had the same issue including a fix whereby you beef up the filtering on the back end of the supply and that is also referenced in the previous thread.
Since then I've been able to relocate a new HF all band antenna closer to the house and so have been able to move the radio indoors. I have been using an Astron RS 35. It developed a problem which I have fixed but it was down for about 2 weeks. So while the Astron was down I went back to the Megawatt to stay on the air. Well here inside the house with it plugged into the wall there is NO LONGER any such noise coming out of it anywhere.
So I am wondering if being powered by the 125' run of extension cord - the cord was acting as an antenna or something and inducing the supply to create or pass along something that was being picked up by this long run of cord? I can't think of anything else accounting for it to produce this noise in one operating location and not the other.
Any ideas?
 

Recon

NY 881
Jul 28, 2019
940
1,153
153
Up-State NY
Posted this occurrence on earlier thread. Noticed several months ago when running my HF rig on the Megawatt S12 400 I think it is .... the 36 amp one, that it was spewing spurious noise every 5-8kc between around 15-23mhz making those freqs nearly unusable. Mainly took away 15 Meters from me. Otherwise was no problem in the other frequency areas. Okay - now the setup was in an outbuilding workshop being fed by 125' feet of extension cord from the house. Web searches indicated that others have had the same issue including a fix whereby you beef up the filtering on the back end of the supply and that is also referenced in the previous thread.
Since then I've been able to relocate a new HF all band antenna closer to the house and so have been able to move the radio indoors. I have been using an Astron RS 35. It developed a problem which I have fixed but it was down for about 2 weeks. So while the Astron was down I went back to the Megawatt to stay on the air. Well here inside the house with it plugged into the wall there is NO LONGER any such noise coming out of it anywhere.
So I am wondering if being powered by the 125' run of extension cord - the cord was acting as an antenna or something and inducing the supply to create or pass along something that was being picked up by this long run of cord? I can't think of anything else accounting for it to produce this noise in one operating location and not the other.
Any ideas?
Wow! A125' extension cord? Is it a 10 gage / 3 wire extension cord?
 

Wire Weasel

Senior Moment
Dec 13, 2008
2,953
589
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Wow! Only 14 gauge? Have you checked the loss?
Apparently not much. That's not extreme at all for AC. Never any issues with running power tools like big saws or the radio setup. Now DC would have been a considerable issue.
 

AudioShockwav

Extraterrestrial
Staff member
Apr 6, 2005
7,854
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Nor Cal Sierra Nevada
Apparently not much. That's not extreme at all for AC. Never any issues with running power tools like big saws or the radio setup. Now DC would have been a considerable issue.
Well maybe.
It might be the voltage drop, 100 feet of hardware store cord , 14 gauge plus 25' more... That's a long run.
If you got 115 at the plug, I would guess the drop gets you 102-103 volts at the end maybe.
Those light duty cords are really light duty.
There's lots of stuff in switching supplies that make noise even the regulator circuit itself.
If on demand you are pulling the voltage down to less than a hundred volts input to the supply maybe that's causing the noise?
Guess?

73
Jeff
 

Wire Weasel

Senior Moment
Dec 13, 2008
2,953
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Never bothered to take any measurements as I've never had any power issues in the outbuilding .... but just for guys I did today.
Fluke 87 III
VAC at back porch outlet 124.3
VAC at end of 125' 14G cord 124.3
VAC with 10" corded circular saw running 120.7
 

AudioShockwav

Extraterrestrial
Staff member
Apr 6, 2005
7,854
6,041
593
Nor Cal Sierra Nevada
Never bothered to take any measurements as I've never had any power issues in the outbuilding .... but just for guys I did today.
Fluke 87 III
VAC at back porch outlet 124.3
VAC at end of 125' 14G cord 124.3
VAC with 10" corded circular saw running 120.7
That rules out voltage drop, it doing much better than I expected out of 14 gauge at that run.

73
Jeff
 
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Dmans

Sr. Member
Jan 22, 2017
1,339
1,694
173
Georgia
How would one see or measure this effect with a test instrument?
You could use a Field Strength meter I would think. I made one out of a $12.00 analog (big box store purchase) battery tester/volt meter.

It looks like this.
IMG_3689.jpg


A couple of diodes a variable resistor and a capacitor is all there is to it (I think), Its been a few years so......
Schematics available via Google or............

73
David
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,992
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Nova Scotia,Canada
Apparently not much. That's not extreme at all for AC. Never any issues with running power tools like big saws or the radio setup. Now DC would have been a considerable issue.

Voltage drop is the same for AC as it is for DC. V= I squared R. That formula is the same regardless of AC or DC. Perhaps you meant that with the higher voltage less current is drawn which will result in less voltage drop. I just wanted to clarify that for the same reason people think that FM will not skip because they equate FM to FM broadcasting which is on VHF. In this case we are comparing DC to 60HZ.
 
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