Hello Wilson:
Each radial (6) is 95 feet long. There are two that are directly under the two
sides of the dipole the other four start out at the feedpoint of the dipole and
the ends are 3 feet apart with respect to the ones that are directly below the
dipole.
I used this low height (20 feet flat) resonant dipole antenna for a long time
without the radials on the ground and it worked great (NVIS). I think it works
better with the radials - but not night and day better.
There was a question about my S0 noise level. That is a result of no switching
supplies in the shack or house and working with the power company and neighbors
to eliminate all man made noise sources. Also correctly grounding and bonding
antennas, towers and shack components. Lots of ferrite in the right places. And
a few visits from K3RFI!
73
Tim K3LR
-----Original Message-----
From: Wilson Lamb [mailto:infomet@embarqmail.com]
Sent: Thursday, June 11, 2020 10:16 AM
To: Tim Duffy
Cc: 'undefined'
Subject: RE: [TowerTalk] NVIS
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
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|