Coiled Power Leads

[Yankee]

While I was sitting here staring out the window at my bird feeder, I was totally bored and wanted something to do, since skip isn't going to cooperate at all this month.

The Uniden 980SSB comes with about 4 feet of heavy Ga stranded copper wire with a fuse in line. For most of the length, the wires are fused together. Near the end I have soldered in a 4 pin Molex connector to fit the Computer Power Supply I have salvaged to run the radio. The PS puts out a good clean 12.07v DC @ 17A. At least the noise at the radio is not bad, unless conditions make it bad. At night, it's almost silent.

So anyway, being bored, I wrapped the last 18 inches or so around a medium sized Sharpie Barrel, I got about 8 or 9 wraps, then taped it a bunch of turns with clear plastic packing box tape. When I pulled the Sharpie out, it held it's shape.

So I plugged the Molex back in, turned on the PS, the radio and found I had just lost a full or little more s number of static. And who doesn't want to get rid of static? By the way, I already have little clamp on ferrites on both ends of the red and black power wires.

Now, a question for people who know these things, is there a better way to get more buzz kill out of this? Is the diameter enough, is the number of wraps enough? Should it be right at the end of the wire before the PS? there isn't much length before the radio though.

 

[Mudfoot]

Might look at the actual ratings of your ferrites. Most of the ones you buy online or at Radio Shack work poorly below 150 MHz. You can test them with a 259 type analyzer. I never buy them unless they have stated specs. Usually mix 31 and 41 are used @ HF frequencies.

Radio Shack ferrites have no use @ HF frequencies.

 

[Yankee]

I hear ya. These are from China, you don't think they would screw me do you? :laugh:

Do you think that "choke" is actually doing anything or is it my imagination?

 

[Mudfoot]

I'm leaning towards wishful thinking.

 

[Yankee]

Yeah, me too. LOL, but, it's done and out of the way, so I'll just leave it there. LOL

 

[Beetle]

As an experiment, try putting a metallic core (maybe a drill bit) in the coil and see if it helps. I doubt it will, but you can try...

 

[Yankee]

Good idea, but it had no effect that I could tell. The only way I have to test it is to turn the squelch down and see if it changed, but there was no change.

 

[W5LZ]

That coiled up power line amounts to a very, very small choke. It's a common way of filtering a power supply along with by-pass capacitors to get rid of 'ripple' noise. Most chokes of this nature use a very large number of turns since the 'ripple' frequency is usually something like 60 to 120 cps/Hrz. Since your power supply is a switching power supply, that 'ripple' is probably something much higher in frequency. That means that the choke would be required to work at that higher frequency and would be more likely to be affective (more -likely- but still not 'large' enough really, it's all frequency related). I'd have to agree, it's probably more a matter of 'wishful thinking' rather than actually doing any 'filtering'. The 'size' of this kind'a choke is current dependent also, has to use wire that is capable of carrying the current produced by the power supply. The larger the current flow the larger the wire.
Wrapping that power line around an iron or ferrite rod is like the core used in a transformer. It can certainly increase the choking action of that choke, but considering the number of turns in the coil, probably not much/enough.
[Completely unrelated, but if you happen to be getting some RF noise in through a microphone that uses a coiled cord, try sticking a ferrite rod (or a graphite pencil) in that coiled cord. It works sometimes.]
It's a very basic use of inductive reactance being useful in certain circumstances.
- 'Doc

 

[Yankee]

Thanks for the explanation Doc. I had read somewhere about people twisting the power leads together, but these were already molded. I could have twisted them too I guess, but wanted to see what the coil might do if anything.

I think next, I will try and find out if I can get that power supply to put out more voltage, like 13.5 instead of 12.07.

 

[KM3F]

Computer power supplies are noisey for radio use.
They are usually a switch type.
You may filter the DC leads but it may still radiate to the antenna direct or from the AC power cord.
Get a good linear (not switch type) power supply that does not generate any noise and runs at the rated voltage.
Good luck.

 

[Yankee]

I am already going one better. I have in the works, a new old stock RCI 2985DX, in the box. I hope to have it in a week or ten days. However, I will still need a powersupply to run the afterburner, and that won't be a refugee from a computer.