Re: Random length wire ant on 160M?

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From: Greg Weinfurtner (weinfurtner@ouvaxa.cats.ohiou.edu)
Date: Mon Nov 20 1995 - 08:40:45 EST


>G'day, everyone.
>I have upgraded to General in the past few weeks and have been having
>quite a bit of fun on 80M and above. In order for me to get on the
>air with as small of an investment as I could (to keep the xyl happy)
>I ended up using just a random length wire antenna with a tuner.
>This works quite well on 80 and 40, but last night the bands were
>dead so I decided to listen in on 160 to see what was going on.
>I was suprised to find that the band had quite a bit of activity
>from one end to the other.
>I was able to get a rather good swr (1.3:1) with the 75' antenna
>but my time was short so I didn't try to make any contacts. My question
>for you is that I was wondering if you know of anyone that has used
>just a simple longwire with any success on 160. I am not looking to
>get dxcc on 160. I just want to get on and have some fun. So any
>comments that you may have would be appreciated.
>I can be reached at:
>
>bishopj@pios.com
>
>Take care and I look forward to your reply.
>
> 73 de Jeff kb8frw

Jeff,
        One of the problems with short, low antenna's on 160 is that their
imput impedance is very low, usuall on the order of a few ohms or tens of
ohms. A very clever trick to overcome this is to intentionally make the
antenna too long. This will make the resistance go up, but also add
inductive impedance. Simply add a series varible capacitor to tune it out.
        I use an "L" shaped antenna on 160 and have had very good results.
Here is an ASCII drawing of it. It is a total of 165 feet long and shows
an impedance of 50 ohms+j88. It is not necessary to know any math or have
expensive imp. bridges to use this ant. Just make the cap variable and
you'll be in the ballpark. Adjust with a SWR meter, cut and try adding or
subtracting to the length. Its not critical at all. The horizontal part
can be routed just about anywhere. Try to make the vertical part as high
as possible.

                         125' horizontal
  @@@______________________________________________@@@____
     |
     |
     | 40' high
     |
     |
    ___ 1000pf capacitor
    ___
     |
     o Feedpoint 50 ohms (@@@=insulator)

     o
     |
    ___
    ///

        For the ground I've tied everything together, furnace ducts, ground
rods, house ground, dogs chain (just kidding! :')) and radial system, with
braid from RG 8/U. Does it work? You bet! 49 states on CW including
Hawaii, and just about that many on SSB with only 100watts output.

        ALSO... I feed it with a tuner as a long wire and with QRP I've
worked both coasts. On the higher bands the capacitor's impedance is so
low it makes practically no difference if you leave it in or take it out.

GL and CU on 160! 73 de

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* NN N SSSSS 888888 OOOOO Greg Weinfurtner AEE BSS *
* N N N S 8 8 O O Electronic Design Splst *
* N N N SSSSS 888888 O O Ohio University Athens *
* N N N S 8 8 O O *
* N NN SSSSS 888888 OOOOO *
* Canst thou send lightnings *
* Amateur Radio NS8O that they may go and say *
* unto thee,'Here we are'? *
* weinfurtner@ouvaxa.cats.ohiou.edu Job 38:35 *
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