[TowerTalk] 160 M OCF antenna
RadioIR at charter.net
Sat Feb 25 20:10:37 EST 2006
"Jerry, It was originally 271' and had a SWR match of 1:1 at 2.1 MHz. I
added 25' and that brought the 1:1 match down to 1.950 MHz...."
That makes more sense. Originally you said you had 86 + 110 + 85 = 281
ft. That where I got that number.
"My ground here is nearly perfect since I'm Oceanside about 13' ASL and
surrounded by ocean on all
sides since I'm on the southern tip of the island, except to the NNW as
this key runs...."
That is the most important piece of information that you gave. Why are
you wasting your time with a horizontal antenna? A vertical (or an
inverted L) over salt water will blow a low dipole away (unless you only
want to work Fl.).
>Jerry, It was originally 271' and had a SWR match of 1:1 at 2.1 MHz. I
>added 25' and that brought the 1:1 match down to 1.950 MHz. Note, I am
>saying SWR match and not resonance which I used before and, of course, could
>be misleading. I have misplaced my MFJ 259 meter so I'm relying on a Daiwa
>SWR bridge to measure this guy. The resonance at 296' should be much lower
>than 2 MHz but I don't know the velocity factor of this insulated wire which
>should push the frequency even lower, not higher. My ground here is nearly
>perfect since I'm Oceanside about 13' ASL and surrounded by ocean on all
>sides since I'm on the southern tip of the island, except to the NNW as
>this key runs.
>I just moved the long end to about 20' elevation and removed the 25' adder
>section. With this configuration, the SWR is now centered at 1.3:1 at 2.04
>MHz. Still too high for a 271' long OCF dipole. I think the idea that the
>proximity to ground is the culprit here is probably correct.
>Jon Hamlet, W4ZW
>Casey Key Island, Florida
>"A little piece of paradise in the Gulf of Mexico"
>From: towertalk-bounces at contesting.com
>[mailto:towertalk-bounces at contesting.com] On Behalf Of K4SAV
>Sent: Saturday, February 25, 2006 5:02 PM
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] 160 M OCF antenna
>Wait a minute!
>You originally had a 281 ft OCF dipole that resonated at 2.1 MHz.
>You then shortened it by 10 ft and moved the resonance to 1.95 MHz?
>Kinda blew my mind there for a second.
>Assuming you are giving us good data, then there are two possibilities.
>1. What you are getting is not the resonant frequency of the antenna, What
>you are getting is the impedance of the antenna, transformed by a highly
>mismatched transmission line. This impedance can be almost anything
>depending on the length of the feedline.
>2. The balun is not working as a current balun, and the feedline is acting
>as part of the antenna. These effects will be difficult to predict.
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