Hi, Joe
Sounds like things are3 progressing nicely! I also live on a small lot and I
worked DX all over the world with and inverted L that only had two elevated
resonant radials at 90 degrees to each other.
Couple comments regarding you VSWR observations;
1.0 A perfectly tuned resonant inverted L over a substantial radial
field will have a VSWR up in the range of 1.5-2.0:1 or a bit higher without
other matching arrangements. The driving point impedance of the inverted L
at resonance will be of the order of 20-35 ohms or so, with a good
ground/radial system, which would put the VSWR at resonance up in the range
of 1.5 -2.0 or so.
2.0 It can be shown that minimum VSWR will occur at resonance.
3.0 Therefore, your observation of a VSWR variation of 2.1-1.7 as you
tune from 1.8-2.0 MHz indicates that your radiator is a little short with
its resonance at or above the top end of the band at 2.0 MHz and needs to be
lengthened a little to move the resonance lower in the band. May need
another 1-2 feet or so of wire. Just remember that minimum VSWR WILL occur
at resonance.
Sounds like your relocated Inverted L is working fairly well! Have fun!!
And BTW, I've had great success hanging 160m inverted Ls and 80m
ground-planes from trees! Even built a KILLER 80m 5-element steerable array
for a friend that was supported by oak trees! We didn't have to wait for
anyone -anywhere in the world on 80 or 75 meters!! Trees work OK!
Have fun!
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Joe
Galicic
Sent: Monday, November 24, 2014 3:22 PM
To: Guy Olinger K2AV
Cc: Richard Fry; List, TopBand
Subject: Re: Topband: Broadband Inverted L
Update --
I've added 13 radials to my new L over last weekend. Ranging from 30 to 65
feet. Also connected radials to old radial field. New radials run over top
of old the ones. Due to antenna placement and neighbors I can only run
radials 90 degrees from the antenna base. Cant run radials 360 degrees. No
matter how much I try to tune the radiator wire the SWR remains the same at
2.1-1.7 (1.8-2.0MHZ). I think the tree is causing that. The wire runs
directly up the center of the tree and out over the top branches. It's #14
stranded wire with jacket. The antenna is probably still very inefficient?
I now notice much better receive and transmit performance than before.
Before I added the radials the old L was louder in certain directions.
That's not the case any more. The new L is louder now regardless of
direction. So I'm heading in the right direction. I was able to work 3 new
DX entities on 160 including Italy with only 100 watts CW. The DX was about
1-2 S units louder on the new L.
Thanks for all of the helpful suggestions !! It's not easy trying to put up
an efficient antenna for 160 on a small lot !
Joe
----- Original Message -----
From: "Guy Olinger K2AV" <k2av.guy@gmail.com>
To: "Richard Fry" <rfry@adams.net>
Cc: "List, TopBand" <topband@contesting.com>
Sent: Monday, November 24, 2014 12:27:01 PM
Subject: Re: Topband: Broadband Inverted L
The somewhat devastating report from NEC 4.2 offered by Mr Fry is all the
more gloomy if one factors in the now-common acknowledgement that NEC 4.x
underestimates ground losses with less than ideal radial configurations. Or
stated another way, the gloomy NEC 4.2 report is the very best the bad
situation could be, and likely is significantly worse.
The "shape" of radiation patterns of this genre of antenna rarely depend on
radials. The "magnitude" of the pattern depends on the radials. Mr. Fry's
link shows a very typical shape to the pattern, also seen in an L with a
"gold standard" radial system, the latter being much louder at the distant
end.
73, Guy.
On Mon, Nov 24, 2014 at 9:05 AM, Richard Fry <rfry@adams.net> wrote:
> Joe N3HEE wrote:
>
>> I moved my 160 inverted L to a tall tree in my backyard to get more
>> vertical height. The vertical leg is now about 65 feet and the rest
>> (65feet) is horizontal. .... Any feedback would be great. Thanks -Joe
>> N3HEE
>>
> __________
>
> A NEC4.2 model roughly approximating this system was made using a set
> of
> 40 symmetrically-buried radials each 50 feet long, and connected at
> their common point by a 40-ft straight wire lying on the earth to an
> 8-ft buried ground rod 40 feet away. The L consisted of a vertical and
> a horizontal conductor of 65 feet each. The vertical axes of the
> vertical conductor of the L and of the offset 8-ft ground rod were
> aligned. A second 8-ft ground rod was located at the common-point of the
radial field.
>
> The radiation resistance of the L on 1.9 MHz is 21 ohms. System
> results for 1.9 MHz and earth conductivity of 5 mS/m, d.c. 13 ...
>
> Using the offset radial system: Feedpoint Z = 128 -j 3 ohms, peak gain
> = -
> 5.8 dBi at 64 degrees elevation, 2:1 SWR BW = 270 kHz, system
> radiation efficiency = 16.4%
>
> With the vertical conductor of the L centered over the common point of
> the
> radials: Feedpoint Z = 29 +j 4 ohms, peak gain = 0.5 dBi at 64 degrees
> elevation, 2:1 SWR BW = 90 kHz, system radiation efficiency = 72.4%
>
> The efficiency numbers above are based on a lossless match to the
> transmission line connected at the feedpoint. The NEC gain analyses
> were based on the far field.
>
> For this comparison study, NEC4.2 shows a system loss of more than 6
> dB when the L uses the offset radial field, however the offset system
> has the better SWR bandwidth.
>
> R. Fry
>
>
>
>
>
>
>
>
> _________________
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