Coax longwire and impedance

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espenfjo
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Joined: Fri Dec 28, 2018 7:48 pm

Coax longwire and impedance

Post by espenfjo » Fri Jan 18, 2019 2:23 pm

Hi,
I have about 20m / 65ft of RG58C/U which I am using as a longwire. No feed wire, just the coax directly connected to the P an N terminals of the RSP 2.

How do I correctly calculate the impedance to ensure that I use the correct UnUn of this?
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g1hbe
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Location: Cheshire, UK

Re: Coax longwire and impedance

Post by g1hbe » Fri Jan 18, 2019 5:50 pm

Any particular reason you are using coax in this way? P and N are balanced, so the signal seen by the RX will be only the result of any unbalance in the coax. To make it work properly you need some kind of antenna, using the coax as a feeder.

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Andy

espenfjo
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Joined: Fri Dec 28, 2018 7:48 pm

Re: Coax longwire and impedance

Post by espenfjo » Fri Jan 18, 2019 7:10 pm

Mostly because I have 20m of coax lying around. I live in an apartment building, so I do not have any real possibilities for building a large antenna for LW/MW/SW. Streching a coax (or any kind of wire) out a window and about 7-10m to a balcony on the other hand should be doable.

I also have the 1:9 NooElec balun, but were thinking about making something more suitable for this specific case.
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arcosine
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Re: Coax longwire and impedance

Post by arcosine » Tue Jan 22, 2019 3:23 pm

Are you using it as a long wire or as a loop? 20 ft doesn't really classify as a long wire, You would be better off using unbalanced input one not connecting the shield, or two wires, one to each balanced input as a dipole. The formula for a 1/4 wave antenna is 468/2f f in mhz. 20 ft is resonate near 12 MHz. A full wave length loop would be close to the balanced input impedance.

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Tony
AA9CC

espenfjo
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Joined: Fri Dec 28, 2018 7:48 pm

Re: Coax longwire and impedance

Post by espenfjo » Tue Jan 22, 2019 3:37 pm

Im using it as a "long wire", yes. I dont really have the space for creating a dipole (folded or not) tuned for 80m or lower. (20-30m and lower is what is most interesting for me).

Its by the way about 65 feet (20 meters). About half is wound a couple of times between two beams on a balcony, so its not 20m/65ft of straight wire.

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arcosine
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Re: Coax longwire and impedance

Post by arcosine » Tue Jan 22, 2019 3:54 pm

They allowed me to put up a 40 meter dipole on the condo roof, until I interfered with all the cable TVs, so I went stealth, but still interfered. I use to live on the third floor and Id hang a thin, almost invisible wire down at night, then take it up when done. Receiving only should be no problem.

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Tony
AA9CC

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