Pete,
I was going to suggest possible interference to your measurement by a local BC
station. I have a couple of very strong stations near me, one on 1550 kHz
running 50KW. They are about -3 dBm on my 160 inverted-L. But I just finished
looking at my antenna with my AA-55 Zoom and I saw no issues. In the AZ sun I
saw no display either and had to save traces and come inside :-) One of the
reasons I don't like this box. The FA-VA5 is the only VIA, out of 5, that I
have that I can read in sunlight.
Wes N7WS
On 3/25/2021 11:39 AM, N4ZR wrote:
Thanks to everyone who has replied so far, and apologies - I did a lousy job
of describing the antenna. First off - I set out to make it 1/4 wave
(approximately 128 feet) long, and the starting length of wire (what I
actually put up) was 140 feet. Vertical portion is about 55 feet, and the
horizontal part is more or less level. The feedpoint choke is wound on a #43
core (I think), which may make it a bit more credible. The measured minimum
SWR is 2.2 at 1925 KHz, and resonance (X crossing zero) is at 1983 KHz. All
measurements made at the base of the antenna
Now here's the part I *really* don't understand - at X=0, the R measures 119
ohms. Working from memory, I think the old L was resonant about 1875 KHz, and
the R was on the order of 35 ohms, which I was told made sense for a
quarter-wave with a lossy ground plane. The new numbers make no sense at all
to me.
73, Pete N4ZR
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On 3/25/2021 12:26 PM, Artek Manuals wrote:
Technically the insulation should electrically lengthen the antenna about
1.5-2 % (lower the frequency)
As Wes said the dimensions would be helpful. is the flat op horizontal or
does it slope down if it slopes how low is the far end?
I dont think 17 turns of RG400 is doing much for you on 160M but with a
ground mounted radials (IMO) not likely needed...what is the "R" at X=0.
�Are you measuring R+jX at the antenna or at the shack end of the coax? How
long is the coax
Dave
NR1DX
On 3/25/2021 11:54 AM, Wes wrote:
How long is the vertical section?� The insulation should have minimal effect.
Wes� N7WS
On 3/25/2021 8:07 AM, N4ZR 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...
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