Hi Tim,
What's the orientation of the "radials"?
Are they maybe parallel to the antenna? Cut to be reflectors?
Have you compared that antenna to a higher dipole in about the same orientation?
I'm sure going to listen for it.
WL
----- Tim Duffy <k3lr@k3lr.com> wrote:
> I have lots of experience with NVIS antennas and will share my observations.
>
>
> I am involved with Western Pennsylvania traffic nets on the high end of 80
> meters (75 meters) every morning. I have an NVIS half wave coax fed dipole
> that is resonant at 3.988 MHz (1.1 to 1 VSWR). There are three 3/8 wave
> radials below the antenna element on the ground. The dipole antenna is flat
> (not inverted Vee) at 20 feet above ground.
>
> I have worked very hard to get my RX noise level to less than S zero.
>
> I hear very well with this set up - even stations running less than 5 watts.
> When we do state wide drills - I hear very good out to 650 miles. This NVIS
> design works for me.
>
> You can find me at 3.983 MHz at 9 AM Monday through Saturday and 3.9905 on
> Sunday.
>
> 73
> Tim K3LR
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> Wilson Lamb
> Sent: Wednesday, June 10, 2020 7:08 PM
> To: undefined
> Subject: [TowerTalk] NVIS
>
> I'm claiming no expertise, but taking the nice figure with colored lines I
> make the following observations:
>
> 7' is BAD, for everything.
> 28' wins the vertical race, out to 60 deg.
> 28, 42, and 56 are equal (minor rounding) from 60 to 50 deg.
> Below 50deg, higher is always better, for the heights discussed.
> Between 90 and 60 deg, 14, 28, and 42 are within a 3dB range.
> At 30 deg, 28, 42, and 56 are within a 3dB range.
> At 30 deg, 14' is down 6dB
> The flattening pattern of the 56' antenna is down only 6dB from 28', at
> vertical.
> Since you aren't talking to yourself, I hope, things are better for the 56'
> antenna as you go off vertical.
>
> NOW, I have no idea of the height of the "layer" that may be in use for NVIS
> and, therefor, the distance to stations enjoying signals radiated by
> reflections from 90 to 60 deg from vertical.
> Nor do I have any idea of the reflectivity of said layer and, therefor, how
> many Watts would be needed to make it usable.
>
> Conclusions:
> Unless you REALLY NEED NVIS, you want the highest antenna you can get, up to
> 56' in this set.
> Even if you really need NVIS, 400W on the 56' antenna is as good as 100W on
> the best one.
>
> This confirms the remark I saw "somewhere" that one gives up a lot of
> everything else to get NVIS performance.
> These data also show why a really low antenna performs remarkably well when
> condx are good.
> Tune across a band most anytime and look at signal strengths. Then see how
> many would have been unreadable if two S units weaker!
>
> OK, tell me where I slipped up. My two 80m antennae are at 55 and 65 feet.
> I sure hope I don't have to lower them!
> WL
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