40-meters between your target times of 1000 to 1400 local will be
problematic if the fof2 is not at or above 7-MHz. Here in N. Colorado, of
late, it has been, but over the last couple of years during the lull
between Solar Cycles 24 and 25, NVIS was impossible due to the low fof2
which came in lower than 5 MHz. For a look at the fof2 in your area, check
the following:
Of course, I regularly use the Boulder, Colorado, ionogram as it's only
some 30-miles to my south.
Dave - W?LEV
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On Wed, Sep 6, 2023 at 11:58?AM Barry K3EUI <k3euibarry@...> wrote:
JJ Night
To answer your question¡
There is nothing special about this antenna, other than it is a closed
LOOP of 140 ft heavy wire #10 because I had a few hundred feet of this wire.
I wanted good daytime NVIS antenna for prop of only a few hundred miles
from Phila around 10AM to 2 PM.
I was not interested in a low-angle DX signal for evening use (I have a
vertical that does that well)
The amount of wire did not matter too much (120-140 ft to start).
I feed this with about 75 ft of RG213 (nothing special)
The shape is a rectangle, only 20 ft or so above ground. I had a few big
strong trees as tie points.
I tried a 4:1 balun at first (thinking impedance of 100 ohms) and that did
not work well.
I replaced that with a simple 1:1 BALUN (choke).
At the low height above ground, I expected a lower impedance than putting
it up 50 ft.
I could attach the Nano VNA right at the feedpoint - direct - to avoid the
feedline messing with impedance.
I then hooked it up to a CLC Tuner (in my shack) in case the SWR was high
at the digi part of the band.
Because I had about 140 ft wire in the loop, the resonant point was just
below 7 MHz (about 6.8 MHz).
It worked fine for two weeks, but then I thought maybe I could improve it
by shortening it.
I pruned it back about 10 feet (harder to do for me on a 90 degree day)
and then I saw that the minimum SWR fell around 7.1 MHz, right where I
wanted it.
The NANO VNA that I own is already 3 years old (Amazon model) and I¡¯m
using NANO VNA SAVER app on a Win10 (10 yr old) desktop. I had to make the
CALIB first with a 3-30 MHz span at a 10x mag. That took a few minutes to
do the OPEN, SHORT, and 50 0hm LOAD with the standards that came with the
rig.
I did a sweep from 3-30 MHz using the 50 ohm standard and everything
looked perfect on the 6 graphs.
That was reassuring!
The closed loop works far better than a pair of Hamsticks mounted
horizontally (14 ft total). Well, obviously!
It works just about as well as a simple 66 ft Inverted V center-fed dipole
(my standard) but I see much less QSB on the closed loop than from the
dipole. I like to use 7047 kHz W1AW CW bulletins as my standard to compare
antennas at 9AM to 10AM. And¡ it helps me copy CW by ear.
So nothing special about anything that I did.
I put in a CLC tuner in my shack, and this does sharpen up all of the
graphs, but I did not really need it.
My goal: see if I could build a better DAYTIME NVIS antenna for low part
of the 40m band.
I love the sound card digi modes and FLDIGI and am working on a new 40m
EMCOMM digi mode net which should begin on October 1st: Mid-Atlantic 40m
NBEMS net (7068 kHz vfo).
We plan to run this net every Sunday at 10AM to 11AM for a few months to
see how well ¡°fickle forty¡± does at that hour with THOR22 (checkin) and
THOR56 (traffic). We know that 80m collapses by 10 AM for NVIS.
I really did not need a Nano VNA to build and test this antenna. I am now
doing A/B tests to see if folks I work on 40m digi modes can hear any
differences between the closed loop and Inverted V simple dipole.
I took the back-to-back Hamsticks down (may be good for a portable setup)
And I still have a 36 ft vertical with two above ground radials (upside
down T) for evening DX.
What are you trying to accomplish in your antenna?
Without the SAVER software, I¡¯d be lost (color blind).
de k3eui Barry
near Philly
Sept 06 2023
--
*Dave - W?LEV*
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Dave - W?LEV
