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Long wire measurements

Discussion in 'Scanning & Shortwave Listening' started by Dick Parks, Oct 31, 2018.

  1. Dick Parks

    Dick Parks Supporting Member

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    So I just replaced a 220 foot long wire out to my treeline - with a Fluke meter, I measure -26 volts at the business end. Source impedance is about 200K. What's the DC coming from?


     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    First question is WHY were you hooking a multimeter to the antenna wire? Secondly were you referencing this to a good ground? Lastly it was likely just static buildup on the wire. Long wires will do that. I had a 600 foot long wire at one time that would draw sparks from the end on a cold windy day. Best thing to do is install some sort of static bleeder on it to protect your receiver frontend. Several thousand ohms to ground will do the trick. It could also have been rectified RF if you are reasonably close to an AM broadcast site.
     
  3. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    A long wire hooked to an ignition coil can charge a 12v car battery.
     
  4. Dick Parks

    Dick Parks Supporting Member

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    Curiosity made me connect stuff to the lead. First time I ever heard of static electricity remaining constant for days at a time. But I'm keeping a 30 K bleeder on there!
     
    Shadetree Mechanic likes this.
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Static will remain until it is discharged somehow and hopefully not thru the receiver front end. Do you by chance live within a few miles of an AM broadcast site?
     
  6. Dick Parks

    Dick Parks Supporting Member

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    To make a short story long - A few years back I rigged a long wire antenna out to a tree at the south edge of my palatial estate. I used wire from Radio Shack, and it fell down after a while. I recently found some AWG 16 stainless steel wire on eBay and have rigged a new long wire. But now I’ve made some measurements that leave me a bit confused.

    My house is about 15 feet above my back yard, a swale leading to a pond, with a treeline about 200 feet away. My antenna reaches another 75 feet higher at the far end, and the total run works out to about 214 feet if it were a straight line. It should receive best from stations to the northwest and southeast. There are egg insulators at each end, with a 25-foot lead wire to my radio room. I got my first surprise when I looked at the business end of the antenna with my oscilloscope. I expected a big 60 Hz signal to my local ground, a copper water line that leads eventually to power line ground and to a ground rod next to the house at the back. With no load at all, the scope showed a noisy sine wave of 56.2 volts peak-to-peak with a DC offset of 25.6 volts. A DC offset? Where does that come from? Connecting a decade resistor to ground shows the signal source impedance is about 200K ohms. With a 30K load resistance, average antenna output is about 1.6 volts. Does this mean I could charge a Ni-Cad cell with the antenna?
    What is it? Does stainless steel wire exhibit unusual characteristics? Are there little dissimilar-metal areas every few feet in SS wire? Is there unnoticed dirt on the egg insulators that are allowing DC from the tree to get on the far end of the run? Can there be DC generated by a tree?

    Well, never mind the DC part of the antenna signal; how does it work as a receiving antenna? Plenty fine – I have an old military “morale” SLR receiver in a rack, and there’s a radio shack 4-band radio for everyday use. To protect the radio gear from any storm-related overload, I added an old lightning arrester near the lead-in entry plus a 600-volt, .01 uf paper capacitor to remove the mysterious DC. This antenna brings in plenty of stations to satisfy an occasional SWL guy like me.
     
    Shadetree Mechanic likes this.
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I see something in several events. Dissimilar metals? Possibly - simply due to Stainless Steels' Nickel content to reduce corrosion (a donor - perhaps) but also a magnetic event of the earth's own magnetic field passing - moving thru your antenna - you mentioned a tree by a freshwater pond or lake - even soil conductivity between the waters' own mineral contents and the copper pipes in the ground at the home can induce a current - but you use egg insulators so the only thing I can offer is the air noise as earths moving magnetic field. Even air passing over the antenna can strum an knock electrons off and make a current flow - so air speed, it's humidity can also play a role.

    Now as far as coupling the wire to the earth ground - using the events above makes sense with the offset and noise alone. Galena crystals - silicon carbide - these materials provide some "semiconductor" basics so it's not all tat improbable that the antenna and earth as acting a lot like the plates in a battery with water and air as the electrolyte.
     
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  8. Dick Parks

    Dick Parks Supporting Member

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    Buncha nice guys. Happy to be here!
     
    Shadetree Mechanic likes this.
  9. kopcicle

    kopcicle Well-Known Member

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    Yeah, wait till ya get to know us a lil better ;)
     
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  10. 357magnum

    357magnum Well-Known Member

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    kop , Not us ?;)(y):whistle::eek:o_O:D
     
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