Topband: Elementary Inverted L questions

Wes wes_n7ws at triconet.org
Thu Mar 25 12:22:54 EDT 2021


Where do you get the 35'?

Wes  N7WS


On 3/25/2021 9:08 AM, Dave Cuthbert wrote:
> An EZNEC model of your antenna (height of 35') shows it to be resonant at
> 1865 kHz. The minimum SWR was adjusted to 2:1 by adding GND loss of 8 ohms.
>
> SWR is all you need to tune the antenna. Is minimum SWR at 1977 kHz?
>
> I would add more wire and tune the length for minimum SWR at your frequency
> of interest. While doing that feedpoint shunt inductor (about 4uH is a
> start) can be added to achieve a 1:1 SWR. That does not improve the SWR
> bandwidth though and as I like to roam about the bottom 100kHz in contests
> I don't bother. The antenna tuner takes care of that.
>
>       Dave
>
> On Thu, Mar 25, 2021 at 5:07 AM N4ZR <n4zr at comcast.net> wrote:
>
>> I have been trying to replace my inverted L, which broke a few weeks
>> ago, and am having all sorts of puzzlements. Please be kind - I was a
>> history major.
>>
>> 1.  The inverted L broke at the turn, so I went looking for sturdier
>> wire.  I wound up with some #14 insulated recommended by our local RF
>> maven, and put up 140 feet initially, figuring I would prune it *up*
>> into the CW part of the band.  Imagine my surprise when it showed up
>> resonating at 1977 KHz (on an AA-55 Zoom).  Does insulation have such a
>> profound effect on velocity factor?
>>
>> 2.  My feedpoint arrangement has 17 turns of RG-400 as a common mode
>> choke, with the radial field connected to the RG-400 shield at the
>> antenna end.  Initially I tried measuring the resonance without the
>> radial connection.  No resonance and infinite SWR.  I connected the
>> radial field (8 X 70-foot radials on the ground) and that's when I saw
>> the 1977 KHz resonance (X crossing zero).  SWR at minimum was above
>> 2:1.  Does this make sense?  I know the radial field is inadequate for
>> good performance, but...
>>
>> --
>> 73, Pete N4ZR
>> Check out the new Reverse Beacon Network
>> web server at <http://beta.reversebeacon.net>.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
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